2015-08-25 13:27:53

by Wang Nan

Subject: [PATCH 1/2] perf probe: Prevent segfault when reading probe point with absolute address

'perf probe -l' panic if there is a manually inserted probing point
with absolute address. For example:

# echo 'p:probe/abs_ffffffff811e6615 0xffffffff811e6615' > /sys/kernel/debug/tracing/kprobe_events
# perf probe -l
Segmentation fault (core dumped)

This patch fix this problem by considering the situation that
"tp->symbol == NULL" in find_perf_probe_point_from_dwarf() and
find_perf_probe_point_from_map().

After this patch:

# perf probe -l
probe:abs_ffffffff811e6615 (on SyS_write+5@fs/read_write.c)

And when debug info is missing:

# rm -rf ~/.debug
# mv /lib/modules/4.2.0-rc1+/build/vmlinux /lib/modules/4.2.0-rc1+/build/vmlinux.bak
# perf probe -l
probe:abs_ffffffff811e6615 (on sys_write+5)

Signed-off-by: Wang Nan <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
---
tools/perf/util/probe-event.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index f07374b..6c7e538 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -515,7 +515,7 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
if (ret < 0)
goto error;
addr += stext;
- } else {
+ } else if (tp->symbol) {
addr = kernel_get_symbol_address_by_name(tp->symbol, false);
if (addr == 0)
goto error;
@@ -1815,17 +1815,17 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
{
struct symbol *sym = NULL;
struct map *map;
- u64 addr;
+ u64 addr = tp->address;
int ret = -ENOENT;

if (!is_kprobe) {
map = dso__new_map(tp->module);
if (!map)
goto out;
- addr = tp->address;
sym = map__find_symbol(map, addr, NULL);
} else {
- addr = kernel_get_symbol_address_by_name(tp->symbol, true);
+ if (tp->symbol)
+ addr = kernel_get_symbol_address_by_name(tp->symbol, true);
if (addr) {
addr += tp->offset;
sym = __find_kernel_function(addr, &map);
--
1.8.3.4

2015-08-25 13:27:55

by Wang Nan

Subject: [PATCH 2/2] perf probe: Support probing at absolute address

It should be useful to allow 'perf probe' probe at absolute offset of
a target. For example, when (u)probing at a instruction of a shared
object in a embedded system where debuginfo is not avaliable but we
know the offset of that instruction by manually digging.

This patch enables following perf probe command syntax:

# perf probe +0xffffffff811e6615

And

# perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860

In the above example, we don't need a anchor symbol, so it is possible
to compute absolute addresses using other methods and then use
'perf probe' to create the probing points.

Signed-off-by: Wang Nan <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
---
tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
tools/perf/util/probe-event.h | 3 +
tools/perf/util/probe-finder.c | 21 +-----
3 files changed, 138 insertions(+), 30 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 6c7e538..59de69a4 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
*ptr++ = '\0';
}

- tmp = strdup(arg);
- if (tmp == NULL)
- return -ENOMEM;
+ if (arg[0] == '\0')
+ tmp = NULL;
+ else {
+ tmp = strdup(arg);
+ if (tmp == NULL)
+ return -ENOMEM;
+ }

if (file_spec)
pp->file = tmp;
@@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
return -EINVAL;
}

- if (pp->offset && !pp->function) {
- semantic_error("Offset requires an entry function.\n");
- return -EINVAL;
- }
-
if (pp->retprobe && !pp->function) {
semantic_error("Return probe requires an entry function.\n");
return -EINVAL;
@@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
return -EINVAL;
}

+ if (!pp->function && !pp->offset && !pp->file) {
+ semantic_error("Absolute address should not be zero.\n");
+ return -EINVAL;
+ }
+
pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
pp->lazy_line);
@@ -1609,7 +1613,7 @@ error:
static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
{
char *buf, *tmp;
- char offs[32] = "", line[32] = "", file[32] = "";
+ char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
int ret, len;

buf = zalloc(MAX_CMDLEN);
@@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
if (ret <= 0)
goto error;
}
+ if (!pp->function) {
+ ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
+ if (ret <= 0)
+ goto error;
+ }
if (pp->line) {
ret = e_snprintf(line, 32, ":%d", pp->line);
if (ret <= 0)
@@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
goto error;
}

- if (pp->function)
- ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
- offs, pp->retprobe ? "%return" : "", line,
+ if (pp->function || pp->offset)
+ ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
+ pp->function ? : addr,
+ pp->function ? offs : "",
+ pp->retprobe ? "%return" : "", line,
file);
else
ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
@@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
if (tev->uprobes)
ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
tp->module, tp->address);
+ else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
+ /* Absolute address. See try_to_find_absolute_address() */
+ ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
+ tp->module ?: "", tp->module ? ":" : "",
+ tp->address);
else
ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
tp->module ?: "", tp->module ? ":" : "",
@@ -2572,6 +2588,87 @@ err_out:
goto out;
}

+static int try_to_find_absolute_address(struct perf_probe_event *pev,
+ struct probe_trace_event **tevs)
+{
+ struct perf_probe_point *pp = &pev->point;
+ struct probe_trace_event *tev;
+ struct probe_trace_point *tp;
+ int i, err;
+
+ if (perf_probe_event_need_dwarf(pev) || pev->point.function)
+ return -EINVAL;
+
+ /*
+ * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
+ * absolute address.
+ *
+ * Only one tev can be generated by this.
+ */
+ *tevs = zalloc(sizeof(*tev));
+ if (!*tevs)
+ return -ENOMEM;
+
+ tev = *tevs;
+ tp = &tev->point;
+
+ /*
+ * Don't use tp->offset, use address directly, because
+ * in synthesize_probe_trace_command() address cannot be
+ * zero.
+ */
+ tp->address = pev->point.offset;
+ tp->retprobe = pp->retprobe;
+ tev->uprobes = pev->uprobes;
+
+ err = -ENOMEM;
+ /* Give it a '0x' leading symbol name */
+ if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
+ goto errout;
+
+ /* For kprobe, check range */
+ if ((!tev->uprobes) &&
+ (kprobe_warn_out_range(tev->point.symbol,
+ tev->point.address))) {
+ err = -EACCES;
+ goto errout;
+ }
+
+ if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
+ goto errout;
+
+ if (pev->target) {
+ tp->module = strdup(pev->target);
+ if (!tp->module)
+ goto errout;
+ }
+
+ if (tev->group) {
+ tev->group = strdup(pev->group);
+ if (!tev->group)
+ goto errout;
+ }
+
+ if (pev->event) {
+ tev->event = strdup(pev->event);
+ if (!tev->event)
+ goto errout;
+ }
+
+ tev->nargs = pev->nargs;
+ for (i = 0; i < tev->nargs; i++)
+ copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
+
+ return 1;
+
+errout:
+ if (*tevs) {
+ clear_probe_trace_events(*tevs, 1);
+ *tevs = NULL;
+ }
+ return err;
+}
+
bool __weak arch__prefers_symtab(void) { return false; }

static int convert_to_probe_trace_events(struct perf_probe_event *pev,
@@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
}
}

+ ret = try_to_find_absolute_address(pev, tevs);
+ if (ret > 0)
+ return ret;
+
if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
ret = find_probe_trace_events_from_map(pev, tevs);
if (ret > 0)
@@ -2758,3 +2859,22 @@ end:
return ret;
}

+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
+ struct perf_probe_arg *pvar)
+{
+ tvar->value = strdup(pvar->var);
+ if (tvar->value == NULL)
+ return -ENOMEM;
+ if (pvar->type) {
+ tvar->type = strdup(pvar->type);
+ if (tvar->type == NULL)
+ return -ENOMEM;
+ }
+ if (pvar->name) {
+ tvar->name = strdup(pvar->name);
+ if (tvar->name == NULL)
+ return -ENOMEM;
+ } else
+ tvar->name = NULL;
+ return 0;
+}
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 83ee95e..174a3cf 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
/* Maximum index number of event-name postfix */
#define MAX_EVENT_INDEX 1024

+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
+ struct perf_probe_arg *pvar);
+
#endif /*_PROBE_EVENT_H */
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 7b80f8c..29c43c068 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
char buf[32], *ptr;
int ret = 0;

- if (!is_c_varname(pf->pvar->var)) {
- /* Copy raw parameters */
- pf->tvar->value = strdup(pf->pvar->var);
- if (pf->tvar->value == NULL)
- return -ENOMEM;
- if (pf->pvar->type) {
- pf->tvar->type = strdup(pf->pvar->type);
- if (pf->tvar->type == NULL)
- return -ENOMEM;
- }
- if (pf->pvar->name) {
- pf->tvar->name = strdup(pf->pvar->name);
- if (pf->tvar->name == NULL)
- return -ENOMEM;
- } else
- pf->tvar->name = NULL;
- return 0;
- }
+ /* Copy raw parameters */
+ if (!is_c_varname(pf->pvar->var))
+ return copy_to_probe_trace_arg(pf->tvar, pf->pvar);

if (pf->pvar->name)
pf->tvar->name = strdup(pf->pvar->name);
--
1.8.3.4

2015-08-25 15:32:54

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH 1/2] perf probe: Prevent segfault when reading probe point with absolute address

Em Tue, Aug 25, 2015 at 01:27:35PM +0000, Wang Nan escreveu:
> 'perf probe -l' panic if there is a manually inserted probing point
> with absolute address. For example:

Thanks, tested and applied.

- Arnaldo

2015-08-26 00:02:44

by 平松雅巳 / HIRAMATU，MASAMI

Subject: RE: [PATCH 2/2] perf probe: Support probing at absolute address

> From: Wang Nan [mailto:[email protected]]
>
> It should be useful to allow 'perf probe' probe at absolute offset of
> a target. For example, when (u)probing at a instruction of a shared
> object in a embedded system where debuginfo is not avaliable but we
> know the offset of that instruction by manually digging.
>
> This patch enables following perf probe command syntax:
>
> # perf probe +0xffffffff811e6615
>
> And
>
> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860

Why do we need "+" for the absolute address?
It seems that we can do it if we find that the given probe point
starts with "0x".

Thanks,

>
> In the above example, we don't need a anchor symbol, so it is possible
> to compute absolute addresses using other methods and then use
> 'perf probe' to create the probing points.
>
> Signed-off-by: Wang Nan <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Cc: Namhyung Kim <[email protected]>
> ---
> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> tools/perf/util/probe-event.h | 3 +
> tools/perf/util/probe-finder.c | 21 +-----
> 3 files changed, 138 insertions(+), 30 deletions(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 6c7e538..59de69a4 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> *ptr++ = '\0';
> }
>
> - tmp = strdup(arg);
> - if (tmp == NULL)
> - return -ENOMEM;
> + if (arg[0] == '\0')
> + tmp = NULL;
> + else {
> + tmp = strdup(arg);
> + if (tmp == NULL)
> + return -ENOMEM;
> + }
>
> if (file_spec)
> pp->file = tmp;
> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> return -EINVAL;
> }
>
> - if (pp->offset && !pp->function) {
> - semantic_error("Offset requires an entry function.\n");
> - return -EINVAL;
> - }
> -
> if (pp->retprobe && !pp->function) {
> semantic_error("Return probe requires an entry function.\n");
> return -EINVAL;
> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> return -EINVAL;
> }
>
> + if (!pp->function && !pp->offset && !pp->file) {
> + semantic_error("Absolute address should not be zero.\n");
> + return -EINVAL;
> + }
> +
> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> pp->lazy_line);
> @@ -1609,7 +1613,7 @@ error:
> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> {
> char *buf, *tmp;
> - char offs[32] = "", line[32] = "", file[32] = "";
> + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> int ret, len;
>
> buf = zalloc(MAX_CMDLEN);
> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> if (ret <= 0)
> goto error;
> }
> + if (!pp->function) {
> + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> + if (ret <= 0)
> + goto error;
> + }
> if (pp->line) {
> ret = e_snprintf(line, 32, ":%d", pp->line);
> if (ret <= 0)
> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> goto error;
> }
>
> - if (pp->function)
> - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> - offs, pp->retprobe ? "%return" : "", line,
> + if (pp->function || pp->offset)
> + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> + pp->function ? : addr,
> + pp->function ? offs : "",
> + pp->retprobe ? "%return" : "", line,
> file);
> else
> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> if (tev->uprobes)
> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> tp->module, tp->address);
> + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> + /* Absolute address. See try_to_find_absolute_address() */
> + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> + tp->module ?: "", tp->module ? ":" : "",
> + tp->address);
> else
> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> tp->module ?: "", tp->module ? ":" : "",
> @@ -2572,6 +2588,87 @@ err_out:
> goto out;
> }
>
> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
> + struct probe_trace_event **tevs)
> +{
> + struct perf_probe_point *pp = &pev->point;
> + struct probe_trace_event *tev;
> + struct probe_trace_point *tp;
> + int i, err;
> +
> + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> + return -EINVAL;
> +
> + /*
> + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> + * absolute address.
> + *
> + * Only one tev can be generated by this.
> + */
> + *tevs = zalloc(sizeof(*tev));
> + if (!*tevs)
> + return -ENOMEM;
> +
> + tev = *tevs;
> + tp = &tev->point;
> +
> + /*
> + * Don't use tp->offset, use address directly, because
> + * in synthesize_probe_trace_command() address cannot be
> + * zero.
> + */
> + tp->address = pev->point.offset;
> + tp->retprobe = pp->retprobe;
> + tev->uprobes = pev->uprobes;
> +
> + err = -ENOMEM;
> + /* Give it a '0x' leading symbol name */
> + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> + goto errout;
> +
> + /* For kprobe, check range */
> + if ((!tev->uprobes) &&
> + (kprobe_warn_out_range(tev->point.symbol,
> + tev->point.address))) {
> + err = -EACCES;
> + goto errout;
> + }
> +
> + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> + goto errout;
> +
> + if (pev->target) {
> + tp->module = strdup(pev->target);
> + if (!tp->module)
> + goto errout;
> + }
> +
> + if (tev->group) {
> + tev->group = strdup(pev->group);
> + if (!tev->group)
> + goto errout;
> + }
> +
> + if (pev->event) {
> + tev->event = strdup(pev->event);
> + if (!tev->event)
> + goto errout;
> + }
> +
> + tev->nargs = pev->nargs;
> + for (i = 0; i < tev->nargs; i++)
> + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> +
> + return 1;
> +
> +errout:
> + if (*tevs) {
> + clear_probe_trace_events(*tevs, 1);
> + *tevs = NULL;
> + }
> + return err;
> +}
> +
> bool __weak arch__prefers_symtab(void) { return false; }
>
> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> }
> }
>
> + ret = try_to_find_absolute_address(pev, tevs);
> + if (ret > 0)
> + return ret;
> +
> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> ret = find_probe_trace_events_from_map(pev, tevs);
> if (ret > 0)
> @@ -2758,3 +2859,22 @@ end:
> return ret;
> }
>
> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> + struct perf_probe_arg *pvar)
> +{
> + tvar->value = strdup(pvar->var);
> + if (tvar->value == NULL)
> + return -ENOMEM;
> + if (pvar->type) {
> + tvar->type = strdup(pvar->type);
> + if (tvar->type == NULL)
> + return -ENOMEM;
> + }
> + if (pvar->name) {
> + tvar->name = strdup(pvar->name);
> + if (tvar->name == NULL)
> + return -ENOMEM;
> + } else
> + tvar->name = NULL;
> + return 0;
> +}
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 83ee95e..174a3cf 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> /* Maximum index number of event-name postfix */
> #define MAX_EVENT_INDEX 1024
>
> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> + struct perf_probe_arg *pvar);
> +
> #endif /*_PROBE_EVENT_H */
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 7b80f8c..29c43c068 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> char buf[32], *ptr;
> int ret = 0;
>
> - if (!is_c_varname(pf->pvar->var)) {
> - /* Copy raw parameters */
> - pf->tvar->value = strdup(pf->pvar->var);
> - if (pf->tvar->value == NULL)
> - return -ENOMEM;
> - if (pf->pvar->type) {
> - pf->tvar->type = strdup(pf->pvar->type);
> - if (pf->tvar->type == NULL)
> - return -ENOMEM;
> - }
> - if (pf->pvar->name) {
> - pf->tvar->name = strdup(pf->pvar->name);
> - if (pf->tvar->name == NULL)
> - return -ENOMEM;
> - } else
> - pf->tvar->name = NULL;
> - return 0;
> - }
> + /* Copy raw parameters */
> + if (!is_c_varname(pf->pvar->var))
> + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
>
> if (pf->pvar->name)
> pf->tvar->name = strdup(pf->pvar->name);
> --
> 1.8.3.4

????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?

2015-08-26 00:08:12

by 平松雅巳 / HIRAMATU，MASAMI

Subject: RE: [PATCH 1/2] perf probe: Prevent segfault when reading probe point with absolute address

> From: Wang Nan [mailto:[email protected]]
>
> 'perf probe -l' panic if there is a manually inserted probing point
> with absolute address. For example:
>
> # echo 'p:probe/abs_ffffffff811e6615 0xffffffff811e6615' > /sys/kernel/debug/tracing/kprobe_events
> # perf probe -l
> Segmentation fault (core dumped)
>
> This patch fix this problem by considering the situation that
> "tp->symbol == NULL" in find_perf_probe_point_from_dwarf() and
> find_perf_probe_point_from_map().

Oops, OK this is a bug.

Thanks!


Acked-by: Masami Hiramatsu <[email protected]>

>
> After this patch:
>
> # perf probe -l
> probe:abs_ffffffff811e6615 (on SyS_write+5@fs/read_write.c)
>
> And when debug info is missing:
>
> # rm -rf ~/.debug
> # mv /lib/modules/4.2.0-rc1+/build/vmlinux /lib/modules/4.2.0-rc1+/build/vmlinux.bak
> # perf probe -l
> probe:abs_ffffffff811e6615 (on sys_write+5)
>
> Signed-off-by: Wang Nan <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Masami Hiramatsu <[email protected]>
> Cc: Namhyung Kim <[email protected]>
> ---
> tools/perf/util/probe-event.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index f07374b..6c7e538 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -515,7 +515,7 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
> if (ret < 0)
> goto error;
> addr += stext;
> - } else {
> + } else if (tp->symbol) {
> addr = kernel_get_symbol_address_by_name(tp->symbol, false);
> if (addr == 0)
> goto error;
> @@ -1815,17 +1815,17 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
> {
> struct symbol *sym = NULL;
> struct map *map;
> - u64 addr;
> + u64 addr = tp->address;
> int ret = -ENOENT;
>
> if (!is_kprobe) {
> map = dso__new_map(tp->module);
> if (!map)
> goto out;
> - addr = tp->address;
> sym = map__find_symbol(map, addr, NULL);
> } else {
> - addr = kernel_get_symbol_address_by_name(tp->symbol, true);
> + if (tp->symbol)
> + addr = kernel_get_symbol_address_by_name(tp->symbol, true);
> if (addr) {
> addr += tp->offset;
> sym = __find_kernel_function(addr, &map);
> --
> 1.8.3.4

????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?

2015-08-26 02:38:57

by Wang Nan

Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
>> From: Wang Nan [mailto:[email protected]]
>>
>> It should be useful to allow 'perf probe' probe at absolute offset of
>> a target. For example, when (u)probing at a instruction of a shared
>> object in a embedded system where debuginfo is not avaliable but we
>> know the offset of that instruction by manually digging.
>>
>> This patch enables following perf probe command syntax:
>>
>> # perf probe +0xffffffff811e6615
>>
>> And
>>
>> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> Why do we need "+" for the absolute address?
> It seems that we can do it if we find that the given probe point
> starts with "0x".
>
> Thanks,

I will change 2/2 as you suggection.

However, we can only ensure that in kernel side symbol never leading
with '0x'. Although I don't think symbol leading with 0x is useful,
it is still possible for a userspace program compiled and linked by
a language other than C produces such symbol. '+' helps us separate
address and function name semantically, make us don't rely on assumption
on function names. If in future we do meet '0x' symbols, I think we still
need the '+' syntax back. But we can do it at that time.

Thank you.


>> In the above example, we don't need a anchor symbol, so it is possible
>> to compute absolute addresses using other methods and then use
>> 'perf probe' to create the probing points.
>>
>> Signed-off-by: Wang Nan <[email protected]>
>> Cc: Arnaldo Carvalho de Melo <[email protected]>
>> Cc: Ingo Molnar <[email protected]>
>> Cc: Masami Hiramatsu <[email protected]>
>> Cc: Namhyung Kim <[email protected]>
>> ---
>> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
>> tools/perf/util/probe-event.h | 3 +
>> tools/perf/util/probe-finder.c | 21 +-----
>> 3 files changed, 138 insertions(+), 30 deletions(-)
>>
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 6c7e538..59de69a4 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>> *ptr++ = '\0';
>> }
>>
>> - tmp = strdup(arg);
>> - if (tmp == NULL)
>> - return -ENOMEM;
>> + if (arg[0] == '\0')
>> + tmp = NULL;
>> + else {
>> + tmp = strdup(arg);
>> + if (tmp == NULL)
>> + return -ENOMEM;
>> + }
>>
>> if (file_spec)
>> pp->file = tmp;
>> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>> return -EINVAL;
>> }
>>
>> - if (pp->offset && !pp->function) {
>> - semantic_error("Offset requires an entry function.\n");
>> - return -EINVAL;
>> - }
>> -
>> if (pp->retprobe && !pp->function) {
>> semantic_error("Return probe requires an entry function.\n");
>> return -EINVAL;
>> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>> return -EINVAL;
>> }
>>
>> + if (!pp->function && !pp->offset && !pp->file) {
>> + semantic_error("Absolute address should not be zero.\n");
>> + return -EINVAL;
>> + }
>> +
>> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
>> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
>> pp->lazy_line);
>> @@ -1609,7 +1613,7 @@ error:
>> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>> {
>> char *buf, *tmp;
>> - char offs[32] = "", line[32] = "", file[32] = "";
>> + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
>> int ret, len;
>>
>> buf = zalloc(MAX_CMDLEN);
>> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>> if (ret <= 0)
>> goto error;
>> }
>> + if (!pp->function) {
>> + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
>> + if (ret <= 0)
>> + goto error;
>> + }
>> if (pp->line) {
>> ret = e_snprintf(line, 32, ":%d", pp->line);
>> if (ret <= 0)
>> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>> goto error;
>> }
>>
>> - if (pp->function)
>> - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
>> - offs, pp->retprobe ? "%return" : "", line,
>> + if (pp->function || pp->offset)
>> + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
>> + pp->function ? : addr,
>> + pp->function ? offs : "",
>> + pp->retprobe ? "%return" : "", line,
>> file);
>> else
>> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
>> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
>> if (tev->uprobes)
>> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
>> tp->module, tp->address);
>> + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
>> + /* Absolute address. See try_to_find_absolute_address() */
>> + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
>> + tp->module ?: "", tp->module ? ":" : "",
>> + tp->address);
>> else
>> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
>> tp->module ?: "", tp->module ? ":" : "",
>> @@ -2572,6 +2588,87 @@ err_out:
>> goto out;
>> }
>>
>> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
>> + struct probe_trace_event **tevs)
>> +{
>> + struct perf_probe_point *pp = &pev->point;
>> + struct probe_trace_event *tev;
>> + struct probe_trace_point *tp;
>> + int i, err;
>> +
>> + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
>> + return -EINVAL;
>> +
>> + /*
>> + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
>> + * absolute address.
>> + *
>> + * Only one tev can be generated by this.
>> + */
>> + *tevs = zalloc(sizeof(*tev));
>> + if (!*tevs)
>> + return -ENOMEM;
>> +
>> + tev = *tevs;
>> + tp = &tev->point;
>> +
>> + /*
>> + * Don't use tp->offset, use address directly, because
>> + * in synthesize_probe_trace_command() address cannot be
>> + * zero.
>> + */
>> + tp->address = pev->point.offset;
>> + tp->retprobe = pp->retprobe;
>> + tev->uprobes = pev->uprobes;
>> +
>> + err = -ENOMEM;
>> + /* Give it a '0x' leading symbol name */
>> + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
>> + goto errout;
>> +
>> + /* For kprobe, check range */
>> + if ((!tev->uprobes) &&
>> + (kprobe_warn_out_range(tev->point.symbol,
>> + tev->point.address))) {
>> + err = -EACCES;
>> + goto errout;
>> + }
>> +
>> + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
>> + goto errout;
>> +
>> + if (pev->target) {
>> + tp->module = strdup(pev->target);
>> + if (!tp->module)
>> + goto errout;
>> + }
>> +
>> + if (tev->group) {
>> + tev->group = strdup(pev->group);
>> + if (!tev->group)
>> + goto errout;
>> + }
>> +
>> + if (pev->event) {
>> + tev->event = strdup(pev->event);
>> + if (!tev->event)
>> + goto errout;
>> + }
>> +
>> + tev->nargs = pev->nargs;
>> + for (i = 0; i < tev->nargs; i++)
>> + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
>> +
>> + return 1;
>> +
>> +errout:
>> + if (*tevs) {
>> + clear_probe_trace_events(*tevs, 1);
>> + *tevs = NULL;
>> + }
>> + return err;
>> +}
>> +
>> bool __weak arch__prefers_symtab(void) { return false; }
>>
>> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>> }
>> }
>>
>> + ret = try_to_find_absolute_address(pev, tevs);
>> + if (ret > 0)
>> + return ret;
>> +
>> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
>> ret = find_probe_trace_events_from_map(pev, tevs);
>> if (ret > 0)
>> @@ -2758,3 +2859,22 @@ end:
>> return ret;
>> }
>>
>> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
>> + struct perf_probe_arg *pvar)
>> +{
>> + tvar->value = strdup(pvar->var);
>> + if (tvar->value == NULL)
>> + return -ENOMEM;
>> + if (pvar->type) {
>> + tvar->type = strdup(pvar->type);
>> + if (tvar->type == NULL)
>> + return -ENOMEM;
>> + }
>> + if (pvar->name) {
>> + tvar->name = strdup(pvar->name);
>> + if (tvar->name == NULL)
>> + return -ENOMEM;
>> + } else
>> + tvar->name = NULL;
>> + return 0;
>> +}
>> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
>> index 83ee95e..174a3cf 100644
>> --- a/tools/perf/util/probe-event.h
>> +++ b/tools/perf/util/probe-event.h
>> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
>> /* Maximum index number of event-name postfix */
>> #define MAX_EVENT_INDEX 1024
>>
>> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
>> + struct perf_probe_arg *pvar);
>> +
>> #endif /*_PROBE_EVENT_H */
>> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
>> index 7b80f8c..29c43c068 100644
>> --- a/tools/perf/util/probe-finder.c
>> +++ b/tools/perf/util/probe-finder.c
>> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
>> char buf[32], *ptr;
>> int ret = 0;
>>
>> - if (!is_c_varname(pf->pvar->var)) {
>> - /* Copy raw parameters */
>> - pf->tvar->value = strdup(pf->pvar->var);
>> - if (pf->tvar->value == NULL)
>> - return -ENOMEM;
>> - if (pf->pvar->type) {
>> - pf->tvar->type = strdup(pf->pvar->type);
>> - if (pf->tvar->type == NULL)
>> - return -ENOMEM;
>> - }
>> - if (pf->pvar->name) {
>> - pf->tvar->name = strdup(pf->pvar->name);
>> - if (pf->tvar->name == NULL)
>> - return -ENOMEM;
>> - } else
>> - pf->tvar->name = NULL;
>> - return 0;
>> - }
>> + /* Copy raw parameters */
>> + if (!is_c_varname(pf->pvar->var))
>> + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
>>
>> if (pf->pvar->name)
>> pf->tvar->name = strdup(pf->pvar->name);
>> --
>> 1.8.3.4

2015-08-26 09:02:50

by 平松雅巳 / HIRAMATU，MASAMI

Subject: RE: [PATCH 2/2] perf probe: Support probing at absolute address

> From: Wangnan (F) [mailto:[email protected]]
>
> On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
> >> From: Wang Nan [mailto:[email protected]]
> >>
> >> It should be useful to allow 'perf probe' probe at absolute offset of
> >> a target. For example, when (u)probing at a instruction of a shared
> >> object in a embedded system where debuginfo is not avaliable but we
> >> know the offset of that instruction by manually digging.
> >>
> >> This patch enables following perf probe command syntax:
> >>
> >> # perf probe +0xffffffff811e6615
> >>
> >> And
> >>
> >> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> > Why do we need "+" for the absolute address?
> > It seems that we can do it if we find that the given probe point
> > starts with "0x".
> >
> > Thanks,
>
> I will change 2/2 as you suggection.
>
> However, we can only ensure that in kernel side symbol never leading
> with '0x'. Although I don't think symbol leading with 0x is useful,
> it is still possible for a userspace program compiled and linked by
> a language other than C produces such symbol. '+' helps us separate
> address and function name semantically, make us don't rely on assumption
> on function names. If in future we do meet '0x' symbols, I think we still
> need the '+' syntax back. But we can do it at that time.

Agreed, if we really find the case, we can add '+' prefix support
just for an optional expression :)

Thank you!

>
> Thank you.
>
>
> >> In the above example, we don't need a anchor symbol, so it is possible
> >> to compute absolute addresses using other methods and then use
> >> 'perf probe' to create the probing points.
> >>
> >> Signed-off-by: Wang Nan <[email protected]>
> >> Cc: Arnaldo Carvalho de Melo <[email protected]>
> >> Cc: Ingo Molnar <[email protected]>
> >> Cc: Masami Hiramatsu <[email protected]>
> >> Cc: Namhyung Kim <[email protected]>
> >> ---
> >> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> >> tools/perf/util/probe-event.h | 3 +
> >> tools/perf/util/probe-finder.c | 21 +-----
> >> 3 files changed, 138 insertions(+), 30 deletions(-)
> >>
> >> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >> index 6c7e538..59de69a4 100644
> >> --- a/tools/perf/util/probe-event.c
> >> +++ b/tools/perf/util/probe-event.c
> >> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> *ptr++ = '\0';
> >> }
> >>
> >> - tmp = strdup(arg);
> >> - if (tmp == NULL)
> >> - return -ENOMEM;
> >> + if (arg[0] == '\0')
> >> + tmp = NULL;
> >> + else {
> >> + tmp = strdup(arg);
> >> + if (tmp == NULL)
> >> + return -ENOMEM;
> >> + }
> >>
> >> if (file_spec)
> >> pp->file = tmp;
> >> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >> - if (pp->offset && !pp->function) {
> >> - semantic_error("Offset requires an entry function.\n");
> >> - return -EINVAL;
> >> - }
> >> -
> >> if (pp->retprobe && !pp->function) {
> >> semantic_error("Return probe requires an entry function.\n");
> >> return -EINVAL;
> >> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >> + if (!pp->function && !pp->offset && !pp->file) {
> >> + semantic_error("Absolute address should not be zero.\n");
> >> + return -EINVAL;
> >> + }
> >> +
> >> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> >> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> >> pp->lazy_line);
> >> @@ -1609,7 +1613,7 @@ error:
> >> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> {
> >> char *buf, *tmp;
> >> - char offs[32] = "", line[32] = "", file[32] = "";
> >> + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> >> int ret, len;
> >>
> >> buf = zalloc(MAX_CMDLEN);
> >> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> if (ret <= 0)
> >> goto error;
> >> }
> >> + if (!pp->function) {
> >> + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> >> + if (ret <= 0)
> >> + goto error;
> >> + }
> >> if (pp->line) {
> >> ret = e_snprintf(line, 32, ":%d", pp->line);
> >> if (ret <= 0)
> >> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> goto error;
> >> }
> >>
> >> - if (pp->function)
> >> - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> >> - offs, pp->retprobe ? "%return" : "", line,
> >> + if (pp->function || pp->offset)
> >> + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> >> + pp->function ? : addr,
> >> + pp->function ? offs : "",
> >> + pp->retprobe ? "%return" : "", line,
> >> file);
> >> else
> >> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> >> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> >> if (tev->uprobes)
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> >> tp->module, tp->address);
> >> + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> >> + /* Absolute address. See try_to_find_absolute_address() */
> >> + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> >> + tp->module ?: "", tp->module ? ":" : "",
> >> + tp->address);
> >> else
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> >> tp->module ?: "", tp->module ? ":" : "",
> >> @@ -2572,6 +2588,87 @@ err_out:
> >> goto out;
> >> }
> >>
> >> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
> >> + struct probe_trace_event **tevs)
> >> +{
> >> + struct perf_probe_point *pp = &pev->point;
> >> + struct probe_trace_event *tev;
> >> + struct probe_trace_point *tp;
> >> + int i, err;
> >> +
> >> + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> >> + return -EINVAL;
> >> +
> >> + /*
> >> + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> >> + * absolute address.
> >> + *
> >> + * Only one tev can be generated by this.
> >> + */
> >> + *tevs = zalloc(sizeof(*tev));
> >> + if (!*tevs)
> >> + return -ENOMEM;
> >> +
> >> + tev = *tevs;
> >> + tp = &tev->point;
> >> +
> >> + /*
> >> + * Don't use tp->offset, use address directly, because
> >> + * in synthesize_probe_trace_command() address cannot be
> >> + * zero.
> >> + */
> >> + tp->address = pev->point.offset;
> >> + tp->retprobe = pp->retprobe;
> >> + tev->uprobes = pev->uprobes;
> >> +
> >> + err = -ENOMEM;
> >> + /* Give it a '0x' leading symbol name */
> >> + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> >> + goto errout;
> >> +
> >> + /* For kprobe, check range */
> >> + if ((!tev->uprobes) &&
> >> + (kprobe_warn_out_range(tev->point.symbol,
> >> + tev->point.address))) {
> >> + err = -EACCES;
> >> + goto errout;
> >> + }
> >> +
> >> + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> >> + goto errout;
> >> +
> >> + if (pev->target) {
> >> + tp->module = strdup(pev->target);
> >> + if (!tp->module)
> >> + goto errout;
> >> + }
> >> +
> >> + if (tev->group) {
> >> + tev->group = strdup(pev->group);
> >> + if (!tev->group)
> >> + goto errout;
> >> + }
> >> +
> >> + if (pev->event) {
> >> + tev->event = strdup(pev->event);
> >> + if (!tev->event)
> >> + goto errout;
> >> + }
> >> +
> >> + tev->nargs = pev->nargs;
> >> + for (i = 0; i < tev->nargs; i++)
> >> + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> >> +
> >> + return 1;
> >> +
> >> +errout:
> >> + if (*tevs) {
> >> + clear_probe_trace_events(*tevs, 1);
> >> + *tevs = NULL;
> >> + }
> >> + return err;
> >> +}
> >> +
> >> bool __weak arch__prefers_symtab(void) { return false; }
> >>
> >> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> }
> >> }
> >>
> >> + ret = try_to_find_absolute_address(pev, tevs);
> >> + if (ret > 0)
> >> + return ret;
> >> +
> >> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> >> ret = find_probe_trace_events_from_map(pev, tevs);
> >> if (ret > 0)
> >> @@ -2758,3 +2859,22 @@ end:
> >> return ret;
> >> }
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> + struct perf_probe_arg *pvar)
> >> +{
> >> + tvar->value = strdup(pvar->var);
> >> + if (tvar->value == NULL)
> >> + return -ENOMEM;
> >> + if (pvar->type) {
> >> + tvar->type = strdup(pvar->type);
> >> + if (tvar->type == NULL)
> >> + return -ENOMEM;
> >> + }
> >> + if (pvar->name) {
> >> + tvar->name = strdup(pvar->name);
> >> + if (tvar->name == NULL)
> >> + return -ENOMEM;
> >> + } else
> >> + tvar->name = NULL;
> >> + return 0;
> >> +}
> >> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> >> index 83ee95e..174a3cf 100644
> >> --- a/tools/perf/util/probe-event.h
> >> +++ b/tools/perf/util/probe-event.h
> >> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> >> /* Maximum index number of event-name postfix */
> >> #define MAX_EVENT_INDEX 1024
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> + struct perf_probe_arg *pvar);
> >> +
> >> #endif /*_PROBE_EVENT_H */
> >> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> >> index 7b80f8c..29c43c068 100644
> >> --- a/tools/perf/util/probe-finder.c
> >> +++ b/tools/perf/util/probe-finder.c
> >> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> >> char buf[32], *ptr;
> >> int ret = 0;
> >>
> >> - if (!is_c_varname(pf->pvar->var)) {
> >> - /* Copy raw parameters */
> >> - pf->tvar->value = strdup(pf->pvar->var);
> >> - if (pf->tvar->value == NULL)
> >> - return -ENOMEM;
> >> - if (pf->pvar->type) {
> >> - pf->tvar->type = strdup(pf->pvar->type);
> >> - if (pf->tvar->type == NULL)
> >> - return -ENOMEM;
> >> - }
> >> - if (pf->pvar->name) {
> >> - pf->tvar->name = strdup(pf->pvar->name);
> >> - if (pf->tvar->name == NULL)
> >> - return -ENOMEM;
> >> - } else
> >> - pf->tvar->name = NULL;
> >> - return 0;
> >> - }
> >> + /* Copy raw parameters */
> >> + if (!is_c_varname(pf->pvar->var))
> >> + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
> >>
> >> if (pf->pvar->name)
> >> pf->tvar->name = strdup(pf->pvar->name);
> >> --
> >> 1.8.3.4
>

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2015-08-26 13:00:39

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

Em Wed, Aug 26, 2015 at 12:02:40AM +0000, 平松雅巳 / HIRAMATU，MASAMI escreveu:
> > From: Wang Nan [mailto:[email protected]]
> >
> > It should be useful to allow 'perf probe' probe at absolute offset of
> > a target. For example, when (u)probing at a instruction of a shared
> > object in a embedded system where debuginfo is not avaliable but we
> > know the offset of that instruction by manually digging.
> >
> > This patch enables following perf probe command syntax:
> >
> > # perf probe +0xffffffff811e6615
> >
> > And
> >
> > # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
>
> Why do we need "+" for the absolute address?

I guess 'absolute' was the misleading term here, 'offset' would be
better, perhaps, or even 'raw' address.

> It seems that we can do it if we find that the given probe point
> starts with "0x".

Which is kinda ok, since that is the most common way of expressing
offsets, but i don't know why we would preclude using, say, decimal,
octal, etc.

- Arnaldo

> Thanks,
>
> >
> > In the above example, we don't need a anchor symbol, so it is possible
> > to compute absolute addresses using other methods and then use
> > 'perf probe' to create the probing points.
> >
> > Signed-off-by: Wang Nan <[email protected]>
> > Cc: Arnaldo Carvalho de Melo <[email protected]>
> > Cc: Ingo Molnar <[email protected]>
> > Cc: Masami Hiramatsu <[email protected]>
> > Cc: Namhyung Kim <[email protected]>
> > ---
> > tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> > tools/perf/util/probe-event.h | 3 +
> > tools/perf/util/probe-finder.c | 21 +-----
> > 3 files changed, 138 insertions(+), 30 deletions(-)
> >
> > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> > index 6c7e538..59de69a4 100644
> > --- a/tools/perf/util/probe-event.c
> > +++ b/tools/perf/util/probe-event.c
> > @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> > *ptr++ = '\0';
> > }
> >
> > - tmp = strdup(arg);
> > - if (tmp == NULL)
> > - return -ENOMEM;
> > + if (arg[0] == '\0')
> > + tmp = NULL;
> > + else {
> > + tmp = strdup(arg);
> > + if (tmp == NULL)
> > + return -ENOMEM;
> > + }
> >
> > if (file_spec)
> > pp->file = tmp;
> > @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> > return -EINVAL;
> > }
> >
> > - if (pp->offset && !pp->function) {
> > - semantic_error("Offset requires an entry function.\n");
> > - return -EINVAL;
> > - }
> > -
> > if (pp->retprobe && !pp->function) {
> > semantic_error("Return probe requires an entry function.\n");
> > return -EINVAL;
> > @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> > return -EINVAL;
> > }
> >
> > + if (!pp->function && !pp->offset && !pp->file) {
> > + semantic_error("Absolute address should not be zero.\n");
> > + return -EINVAL;
> > + }
> > +
> > pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> > pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> > pp->lazy_line);
> > @@ -1609,7 +1613,7 @@ error:
> > static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> > {
> > char *buf, *tmp;
> > - char offs[32] = "", line[32] = "", file[32] = "";
> > + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> > int ret, len;
> >
> > buf = zalloc(MAX_CMDLEN);
> > @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> > if (ret <= 0)
> > goto error;
> > }
> > + if (!pp->function) {
> > + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> > + if (ret <= 0)
> > + goto error;
> > + }
> > if (pp->line) {
> > ret = e_snprintf(line, 32, ":%d", pp->line);
> > if (ret <= 0)
> > @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> > goto error;
> > }
> >
> > - if (pp->function)
> > - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> > - offs, pp->retprobe ? "%return" : "", line,
> > + if (pp->function || pp->offset)
> > + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> > + pp->function ? : addr,
> > + pp->function ? offs : "",
> > + pp->retprobe ? "%return" : "", line,
> > file);
> > else
> > ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> > @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> > if (tev->uprobes)
> > ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> > tp->module, tp->address);
> > + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> > + /* Absolute address. See try_to_find_absolute_address() */
> > + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> > + tp->module ?: "", tp->module ? ":" : "",
> > + tp->address);
> > else
> > ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> > tp->module ?: "", tp->module ? ":" : "",
> > @@ -2572,6 +2588,87 @@ err_out:
> > goto out;
> > }
> >
> > +static int try_to_find_absolute_address(struct perf_probe_event *pev,
> > + struct probe_trace_event **tevs)
> > +{
> > + struct perf_probe_point *pp = &pev->point;
> > + struct probe_trace_event *tev;
> > + struct probe_trace_point *tp;
> > + int i, err;
> > +
> > + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> > + return -EINVAL;
> > +
> > + /*
> > + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> > + * absolute address.
> > + *
> > + * Only one tev can be generated by this.
> > + */
> > + *tevs = zalloc(sizeof(*tev));
> > + if (!*tevs)
> > + return -ENOMEM;
> > +
> > + tev = *tevs;
> > + tp = &tev->point;
> > +
> > + /*
> > + * Don't use tp->offset, use address directly, because
> > + * in synthesize_probe_trace_command() address cannot be
> > + * zero.
> > + */
> > + tp->address = pev->point.offset;
> > + tp->retprobe = pp->retprobe;
> > + tev->uprobes = pev->uprobes;
> > +
> > + err = -ENOMEM;
> > + /* Give it a '0x' leading symbol name */
> > + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> > + goto errout;
> > +
> > + /* For kprobe, check range */
> > + if ((!tev->uprobes) &&
> > + (kprobe_warn_out_range(tev->point.symbol,
> > + tev->point.address))) {
> > + err = -EACCES;
> > + goto errout;
> > + }
> > +
> > + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> > + goto errout;
> > +
> > + if (pev->target) {
> > + tp->module = strdup(pev->target);
> > + if (!tp->module)
> > + goto errout;
> > + }
> > +
> > + if (tev->group) {
> > + tev->group = strdup(pev->group);
> > + if (!tev->group)
> > + goto errout;
> > + }
> > +
> > + if (pev->event) {
> > + tev->event = strdup(pev->event);
> > + if (!tev->event)
> > + goto errout;
> > + }
> > +
> > + tev->nargs = pev->nargs;
> > + for (i = 0; i < tev->nargs; i++)
> > + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> > +
> > + return 1;
> > +
> > +errout:
> > + if (*tevs) {
> > + clear_probe_trace_events(*tevs, 1);
> > + *tevs = NULL;
> > + }
> > + return err;
> > +}
> > +
> > bool __weak arch__prefers_symtab(void) { return false; }
> >
> > static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> > @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> > }
> > }
> >
> > + ret = try_to_find_absolute_address(pev, tevs);
> > + if (ret > 0)
> > + return ret;
> > +
> > if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> > ret = find_probe_trace_events_from_map(pev, tevs);
> > if (ret > 0)
> > @@ -2758,3 +2859,22 @@ end:
> > return ret;
> > }
> >
> > +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> > + struct perf_probe_arg *pvar)
> > +{
> > + tvar->value = strdup(pvar->var);
> > + if (tvar->value == NULL)
> > + return -ENOMEM;
> > + if (pvar->type) {
> > + tvar->type = strdup(pvar->type);
> > + if (tvar->type == NULL)
> > + return -ENOMEM;
> > + }
> > + if (pvar->name) {
> > + tvar->name = strdup(pvar->name);
> > + if (tvar->name == NULL)
> > + return -ENOMEM;
> > + } else
> > + tvar->name = NULL;
> > + return 0;
> > +}
> > diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> > index 83ee95e..174a3cf 100644
> > --- a/tools/perf/util/probe-event.h
> > +++ b/tools/perf/util/probe-event.h
> > @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> > /* Maximum index number of event-name postfix */
> > #define MAX_EVENT_INDEX 1024
> >
> > +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> > + struct perf_probe_arg *pvar);
> > +
> > #endif /*_PROBE_EVENT_H */
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index 7b80f8c..29c43c068 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> > char buf[32], *ptr;
> > int ret = 0;
> >
> > - if (!is_c_varname(pf->pvar->var)) {
> > - /* Copy raw parameters */
> > - pf->tvar->value = strdup(pf->pvar->var);
> > - if (pf->tvar->value == NULL)
> > - return -ENOMEM;
> > - if (pf->pvar->type) {
> > - pf->tvar->type = strdup(pf->pvar->type);
> > - if (pf->tvar->type == NULL)
> > - return -ENOMEM;
> > - }
> > - if (pf->pvar->name) {
> > - pf->tvar->name = strdup(pf->pvar->name);
> > - if (pf->tvar->name == NULL)
> > - return -ENOMEM;
> > - } else
> > - pf->tvar->name = NULL;
> > - return 0;
> > - }
> > + /* Copy raw parameters */
> > + if (!is_c_varname(pf->pvar->var))
> > + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
> >
> > if (pf->pvar->name)
> > pf->tvar->name = strdup(pf->pvar->name);
> > --
> > 1.8.3.4
>

2015-08-26 13:02:30

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
>
> On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
> >>From: Wang Nan [mailto:[email protected]]
> >>
> >>It should be useful to allow 'perf probe' probe at absolute offset of
> >>a target. For example, when (u)probing at a instruction of a shared
> >>object in a embedded system where debuginfo is not avaliable but we
> >>know the offset of that instruction by manually digging.
> >>
> >>This patch enables following perf probe command syntax:
> >>
> >> # perf probe +0xffffffff811e6615
> >>
> >>And
> >>
> >> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> >Why do we need "+" for the absolute address?
> >It seems that we can do it if we find that the given probe point
> >starts with "0x".
> >
> >Thanks,
>
> I will change 2/2 as you suggection.
>
> However, we can only ensure that in kernel side symbol never leading
> with '0x'. Although I don't think symbol leading with 0x is useful,
> it is still possible for a userspace program compiled and linked by
> a language other than C produces such symbol. '+' helps us separate
> address and function name semantically, make us don't rely on assumption
> on function names. If in future we do meet '0x' symbols, I think we still
> need the '+' syntax back. But we can do it at that time.

Agreed, I also think that using '+' is better, but will not dwell on
this so as to make progress :-)

- Arnaldo

> Thank you.
>
>
> >>In the above example, we don't need a anchor symbol, so it is possible
> >>to compute absolute addresses using other methods and then use
> >>'perf probe' to create the probing points.
> >>
> >>Signed-off-by: Wang Nan <[email protected]>
> >>Cc: Arnaldo Carvalho de Melo <[email protected]>
> >>Cc: Ingo Molnar <[email protected]>
> >>Cc: Masami Hiramatsu <[email protected]>
> >>Cc: Namhyung Kim <[email protected]>
> >>---
> >> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> >> tools/perf/util/probe-event.h | 3 +
> >> tools/perf/util/probe-finder.c | 21 +-----
> >> 3 files changed, 138 insertions(+), 30 deletions(-)
> >>
> >>diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >>index 6c7e538..59de69a4 100644
> >>--- a/tools/perf/util/probe-event.c
> >>+++ b/tools/perf/util/probe-event.c
> >>@@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> *ptr++ = '\0';
> >> }
> >>
> >>- tmp = strdup(arg);
> >>- if (tmp == NULL)
> >>- return -ENOMEM;
> >>+ if (arg[0] == '\0')
> >>+ tmp = NULL;
> >>+ else {
> >>+ tmp = strdup(arg);
> >>+ if (tmp == NULL)
> >>+ return -ENOMEM;
> >>+ }
> >>
> >> if (file_spec)
> >> pp->file = tmp;
> >>@@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >>- if (pp->offset && !pp->function) {
> >>- semantic_error("Offset requires an entry function.\n");
> >>- return -EINVAL;
> >>- }
> >>-
> >> if (pp->retprobe && !pp->function) {
> >> semantic_error("Return probe requires an entry function.\n");
> >> return -EINVAL;
> >>@@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >>+ if (!pp->function && !pp->offset && !pp->file) {
> >>+ semantic_error("Absolute address should not be zero.\n");
> >>+ return -EINVAL;
> >>+ }
> >>+
> >> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> >> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> >> pp->lazy_line);
> >>@@ -1609,7 +1613,7 @@ error:
> >> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> {
> >> char *buf, *tmp;
> >>- char offs[32] = "", line[32] = "", file[32] = "";
> >>+ char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> >> int ret, len;
> >>
> >> buf = zalloc(MAX_CMDLEN);
> >>@@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> if (ret <= 0)
> >> goto error;
> >> }
> >>+ if (!pp->function) {
> >>+ ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> >>+ if (ret <= 0)
> >>+ goto error;
> >>+ }
> >> if (pp->line) {
> >> ret = e_snprintf(line, 32, ":%d", pp->line);
> >> if (ret <= 0)
> >>@@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> goto error;
> >> }
> >>
> >>- if (pp->function)
> >>- ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> >>- offs, pp->retprobe ? "%return" : "", line,
> >>+ if (pp->function || pp->offset)
> >>+ ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> >>+ pp->function ? : addr,
> >>+ pp->function ? offs : "",
> >>+ pp->retprobe ? "%return" : "", line,
> >> file);
> >> else
> >> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> >>@@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> >> if (tev->uprobes)
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> >> tp->module, tp->address);
> >>+ else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> >>+ /* Absolute address. See try_to_find_absolute_address() */
> >>+ ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> >>+ tp->module ?: "", tp->module ? ":" : "",
> >>+ tp->address);
> >> else
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> >> tp->module ?: "", tp->module ? ":" : "",
> >>@@ -2572,6 +2588,87 @@ err_out:
> >> goto out;
> >> }
> >>
> >>+static int try_to_find_absolute_address(struct perf_probe_event *pev,
> >>+ struct probe_trace_event **tevs)
> >>+{
> >>+ struct perf_probe_point *pp = &pev->point;
> >>+ struct probe_trace_event *tev;
> >>+ struct probe_trace_point *tp;
> >>+ int i, err;
> >>+
> >>+ if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> >>+ return -EINVAL;
> >>+
> >>+ /*
> >>+ * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> >>+ * absolute address.
> >>+ *
> >>+ * Only one tev can be generated by this.
> >>+ */
> >>+ *tevs = zalloc(sizeof(*tev));
> >>+ if (!*tevs)
> >>+ return -ENOMEM;
> >>+
> >>+ tev = *tevs;
> >>+ tp = &tev->point;
> >>+
> >>+ /*
> >>+ * Don't use tp->offset, use address directly, because
> >>+ * in synthesize_probe_trace_command() address cannot be
> >>+ * zero.
> >>+ */
> >>+ tp->address = pev->point.offset;
> >>+ tp->retprobe = pp->retprobe;
> >>+ tev->uprobes = pev->uprobes;
> >>+
> >>+ err = -ENOMEM;
> >>+ /* Give it a '0x' leading symbol name */
> >>+ if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> >>+ goto errout;
> >>+
> >>+ /* For kprobe, check range */
> >>+ if ((!tev->uprobes) &&
> >>+ (kprobe_warn_out_range(tev->point.symbol,
> >>+ tev->point.address))) {
> >>+ err = -EACCES;
> >>+ goto errout;
> >>+ }
> >>+
> >>+ if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> >>+ goto errout;
> >>+
> >>+ if (pev->target) {
> >>+ tp->module = strdup(pev->target);
> >>+ if (!tp->module)
> >>+ goto errout;
> >>+ }
> >>+
> >>+ if (tev->group) {
> >>+ tev->group = strdup(pev->group);
> >>+ if (!tev->group)
> >>+ goto errout;
> >>+ }
> >>+
> >>+ if (pev->event) {
> >>+ tev->event = strdup(pev->event);
> >>+ if (!tev->event)
> >>+ goto errout;
> >>+ }
> >>+
> >>+ tev->nargs = pev->nargs;
> >>+ for (i = 0; i < tev->nargs; i++)
> >>+ copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> >>+
> >>+ return 1;
> >>+
> >>+errout:
> >>+ if (*tevs) {
> >>+ clear_probe_trace_events(*tevs, 1);
> >>+ *tevs = NULL;
> >>+ }
> >>+ return err;
> >>+}
> >>+
> >> bool __weak arch__prefers_symtab(void) { return false; }
> >>
> >> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >>@@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> }
> >> }
> >>
> >>+ ret = try_to_find_absolute_address(pev, tevs);
> >>+ if (ret > 0)
> >>+ return ret;
> >>+
> >> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> >> ret = find_probe_trace_events_from_map(pev, tevs);
> >> if (ret > 0)
> >>@@ -2758,3 +2859,22 @@ end:
> >> return ret;
> >> }
> >>
> >>+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >>+ struct perf_probe_arg *pvar)
> >>+{
> >>+ tvar->value = strdup(pvar->var);
> >>+ if (tvar->value == NULL)
> >>+ return -ENOMEM;
> >>+ if (pvar->type) {
> >>+ tvar->type = strdup(pvar->type);
> >>+ if (tvar->type == NULL)
> >>+ return -ENOMEM;
> >>+ }
> >>+ if (pvar->name) {
> >>+ tvar->name = strdup(pvar->name);
> >>+ if (tvar->name == NULL)
> >>+ return -ENOMEM;
> >>+ } else
> >>+ tvar->name = NULL;
> >>+ return 0;
> >>+}
> >>diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> >>index 83ee95e..174a3cf 100644
> >>--- a/tools/perf/util/probe-event.h
> >>+++ b/tools/perf/util/probe-event.h
> >>@@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> >> /* Maximum index number of event-name postfix */
> >> #define MAX_EVENT_INDEX 1024
> >>
> >>+int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >>+ struct perf_probe_arg *pvar);
> >>+
> >> #endif /*_PROBE_EVENT_H */
> >>diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> >>index 7b80f8c..29c43c068 100644
> >>--- a/tools/perf/util/probe-finder.c
> >>+++ b/tools/perf/util/probe-finder.c
> >>@@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> >> char buf[32], *ptr;
> >> int ret = 0;
> >>
> >>- if (!is_c_varname(pf->pvar->var)) {
> >>- /* Copy raw parameters */
> >>- pf->tvar->value = strdup(pf->pvar->var);
> >>- if (pf->tvar->value == NULL)
> >>- return -ENOMEM;
> >>- if (pf->pvar->type) {
> >>- pf->tvar->type = strdup(pf->pvar->type);
> >>- if (pf->tvar->type == NULL)
> >>- return -ENOMEM;
> >>- }
> >>- if (pf->pvar->name) {
> >>- pf->tvar->name = strdup(pf->pvar->name);
> >>- if (pf->tvar->name == NULL)
> >>- return -ENOMEM;
> >>- } else
> >>- pf->tvar->name = NULL;
> >>- return 0;
> >>- }
> >>+ /* Copy raw parameters */
> >>+ if (!is_c_varname(pf->pvar->var))
> >>+ return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
> >>
> >> if (pf->pvar->name)
> >> pf->tvar->name = strdup(pf->pvar->name);
> >>--
> >>1.8.3.4
>

2015-08-26 13:19:52

by Wang Nan

Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

On 2015/8/26 21:02, [email protected] wrote:
> Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
>> On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
>>>> From: Wang Nan [mailto:[email protected]]
>>>>
>>>> It should be useful to allow 'perf probe' probe at absolute offset of
>>>> a target. For example, when (u)probing at a instruction of a shared
>>>> object in a embedded system where debuginfo is not avaliable but we
>>>> know the offset of that instruction by manually digging.
>>>>
>>>> This patch enables following perf probe command syntax:
>>>>
>>>> # perf probe +0xffffffff811e6615
>>>>
>>>> And
>>>>
>>>> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
>>> Why do we need "+" for the absolute address?
>>> It seems that we can do it if we find that the given probe point
>>> starts with "0x".
>>>
>>> Thanks,
>> I will change 2/2 as you suggection.
>>
>> However, we can only ensure that in kernel side symbol never leading
>> with '0x'. Although I don't think symbol leading with 0x is useful,
>> it is still possible for a userspace program compiled and linked by
>> a language other than C produces such symbol. '+' helps us separate
>> address and function name semantically, make us don't rely on assumption
>> on function names. If in future we do meet '0x' symbols, I think we still
>> need the '+' syntax back. But we can do it at that time.
> Agreed, I also think that using '+' is better, but will not dwell on
> this so as to make progress :-)
>
> - Arnaldo
>

Maybe we should support both of them, making '+0x1234' the core
syntax, and '0x1234' style as a syntax sugar. However I have worked
on this problem for nearly a full day but my main work should be BPF
related things...

Since Masami has acked all of the 6 v3 patches, if we still need '+' I can
bring it back with a new patch when I have time. However, same to you,
I don't think this should be a blocking problem.

Thank you.

>> Thank you.
>>
>>
>>>> In the above example, we don't need a anchor symbol, so it is possible
>>>> to compute absolute addresses using other methods and then use
>>>> 'perf probe' to create the probing points.
>>>>
>>>> Signed-off-by: Wang Nan <[email protected]>
>>>> Cc: Arnaldo Carvalho de Melo <[email protected]>
>>>> Cc: Ingo Molnar <[email protected]>
>>>> Cc: Masami Hiramatsu <[email protected]>
>>>> Cc: Namhyung Kim <[email protected]>
>>>> ---
>>>> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
>>>> tools/perf/util/probe-event.h | 3 +
>>>> tools/perf/util/probe-finder.c | 21 +-----
>>>> 3 files changed, 138 insertions(+), 30 deletions(-)
>>>>
>>>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>>>> index 6c7e538..59de69a4 100644
>>>> --- a/tools/perf/util/probe-event.c
>>>> +++ b/tools/perf/util/probe-event.c
>>>> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>>>> *ptr++ = '\0';
>>>> }
>>>>
>>>> - tmp = strdup(arg);
>>>> - if (tmp == NULL)
>>>> - return -ENOMEM;
>>>> + if (arg[0] == '\0')
>>>> + tmp = NULL;
>>>> + else {
>>>> + tmp = strdup(arg);
>>>> + if (tmp == NULL)
>>>> + return -ENOMEM;
>>>> + }
>>>>
>>>> if (file_spec)
>>>> pp->file = tmp;
>>>> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>>>> return -EINVAL;
>>>> }
>>>>
>>>> - if (pp->offset && !pp->function) {
>>>> - semantic_error("Offset requires an entry function.\n");
>>>> - return -EINVAL;
>>>> - }
>>>> -
>>>> if (pp->retprobe && !pp->function) {
>>>> semantic_error("Return probe requires an entry function.\n");
>>>> return -EINVAL;
>>>> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
>>>> return -EINVAL;
>>>> }
>>>>
>>>> + if (!pp->function && !pp->offset && !pp->file) {
>>>> + semantic_error("Absolute address should not be zero.\n");
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
>>>> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
>>>> pp->lazy_line);
>>>> @@ -1609,7 +1613,7 @@ error:
>>>> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>>>> {
>>>> char *buf, *tmp;
>>>> - char offs[32] = "", line[32] = "", file[32] = "";
>>>> + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
>>>> int ret, len;
>>>>
>>>> buf = zalloc(MAX_CMDLEN);
>>>> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>>>> if (ret <= 0)
>>>> goto error;
>>>> }
>>>> + if (!pp->function) {
>>>> + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
>>>> + if (ret <= 0)
>>>> + goto error;
>>>> + }
>>>> if (pp->line) {
>>>> ret = e_snprintf(line, 32, ":%d", pp->line);
>>>> if (ret <= 0)
>>>> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>>>> goto error;
>>>> }
>>>>
>>>> - if (pp->function)
>>>> - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
>>>> - offs, pp->retprobe ? "%return" : "", line,
>>>> + if (pp->function || pp->offset)
>>>> + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
>>>> + pp->function ? : addr,
>>>> + pp->function ? offs : "",
>>>> + pp->retprobe ? "%return" : "", line,
>>>> file);
>>>> else
>>>> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
>>>> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
>>>> if (tev->uprobes)
>>>> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
>>>> tp->module, tp->address);
>>>> + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
>>>> + /* Absolute address. See try_to_find_absolute_address() */
>>>> + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
>>>> + tp->module ?: "", tp->module ? ":" : "",
>>>> + tp->address);
>>>> else
>>>> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
>>>> tp->module ?: "", tp->module ? ":" : "",
>>>> @@ -2572,6 +2588,87 @@ err_out:
>>>> goto out;
>>>> }
>>>>
>>>> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
>>>> + struct probe_trace_event **tevs)
>>>> +{
>>>> + struct perf_probe_point *pp = &pev->point;
>>>> + struct probe_trace_event *tev;
>>>> + struct probe_trace_point *tp;
>>>> + int i, err;
>>>> +
>>>> + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
>>>> + return -EINVAL;
>>>> +
>>>> + /*
>>>> + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
>>>> + * absolute address.
>>>> + *
>>>> + * Only one tev can be generated by this.
>>>> + */
>>>> + *tevs = zalloc(sizeof(*tev));
>>>> + if (!*tevs)
>>>> + return -ENOMEM;
>>>> +
>>>> + tev = *tevs;
>>>> + tp = &tev->point;
>>>> +
>>>> + /*
>>>> + * Don't use tp->offset, use address directly, because
>>>> + * in synthesize_probe_trace_command() address cannot be
>>>> + * zero.
>>>> + */
>>>> + tp->address = pev->point.offset;
>>>> + tp->retprobe = pp->retprobe;
>>>> + tev->uprobes = pev->uprobes;
>>>> +
>>>> + err = -ENOMEM;
>>>> + /* Give it a '0x' leading symbol name */
>>>> + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
>>>> + goto errout;
>>>> +
>>>> + /* For kprobe, check range */
>>>> + if ((!tev->uprobes) &&
>>>> + (kprobe_warn_out_range(tev->point.symbol,
>>>> + tev->point.address))) {
>>>> + err = -EACCES;
>>>> + goto errout;
>>>> + }
>>>> +
>>>> + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
>>>> + goto errout;
>>>> +
>>>> + if (pev->target) {
>>>> + tp->module = strdup(pev->target);
>>>> + if (!tp->module)
>>>> + goto errout;
>>>> + }
>>>> +
>>>> + if (tev->group) {
>>>> + tev->group = strdup(pev->group);
>>>> + if (!tev->group)
>>>> + goto errout;
>>>> + }
>>>> +
>>>> + if (pev->event) {
>>>> + tev->event = strdup(pev->event);
>>>> + if (!tev->event)
>>>> + goto errout;
>>>> + }
>>>> +
>>>> + tev->nargs = pev->nargs;
>>>> + for (i = 0; i < tev->nargs; i++)
>>>> + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
>>>> +
>>>> + return 1;
>>>> +
>>>> +errout:
>>>> + if (*tevs) {
>>>> + clear_probe_trace_events(*tevs, 1);
>>>> + *tevs = NULL;
>>>> + }
>>>> + return err;
>>>> +}
>>>> +
>>>> bool __weak arch__prefers_symtab(void) { return false; }
>>>>
>>>> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>>>> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
>>>> }
>>>> }
>>>>
>>>> + ret = try_to_find_absolute_address(pev, tevs);
>>>> + if (ret > 0)
>>>> + return ret;
>>>> +
>>>> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
>>>> ret = find_probe_trace_events_from_map(pev, tevs);
>>>> if (ret > 0)
>>>> @@ -2758,3 +2859,22 @@ end:
>>>> return ret;
>>>> }
>>>>
>>>> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
>>>> + struct perf_probe_arg *pvar)
>>>> +{
>>>> + tvar->value = strdup(pvar->var);
>>>> + if (tvar->value == NULL)
>>>> + return -ENOMEM;
>>>> + if (pvar->type) {
>>>> + tvar->type = strdup(pvar->type);
>>>> + if (tvar->type == NULL)
>>>> + return -ENOMEM;
>>>> + }
>>>> + if (pvar->name) {
>>>> + tvar->name = strdup(pvar->name);
>>>> + if (tvar->name == NULL)
>>>> + return -ENOMEM;
>>>> + } else
>>>> + tvar->name = NULL;
>>>> + return 0;
>>>> +}
>>>> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
>>>> index 83ee95e..174a3cf 100644
>>>> --- a/tools/perf/util/probe-event.h
>>>> +++ b/tools/perf/util/probe-event.h
>>>> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
>>>> /* Maximum index number of event-name postfix */
>>>> #define MAX_EVENT_INDEX 1024
>>>>
>>>> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
>>>> + struct perf_probe_arg *pvar);
>>>> +
>>>> #endif /*_PROBE_EVENT_H */
>>>> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
>>>> index 7b80f8c..29c43c068 100644
>>>> --- a/tools/perf/util/probe-finder.c
>>>> +++ b/tools/perf/util/probe-finder.c
>>>> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
>>>> char buf[32], *ptr;
>>>> int ret = 0;
>>>>
>>>> - if (!is_c_varname(pf->pvar->var)) {
>>>> - /* Copy raw parameters */
>>>> - pf->tvar->value = strdup(pf->pvar->var);
>>>> - if (pf->tvar->value == NULL)
>>>> - return -ENOMEM;
>>>> - if (pf->pvar->type) {
>>>> - pf->tvar->type = strdup(pf->pvar->type);
>>>> - if (pf->tvar->type == NULL)
>>>> - return -ENOMEM;
>>>> - }
>>>> - if (pf->pvar->name) {
>>>> - pf->tvar->name = strdup(pf->pvar->name);
>>>> - if (pf->tvar->name == NULL)
>>>> - return -ENOMEM;
>>>> - } else
>>>> - pf->tvar->name = NULL;
>>>> - return 0;
>>>> - }
>>>> + /* Copy raw parameters */
>>>> + if (!is_c_varname(pf->pvar->var))
>>>> + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
>>>>
>>>> if (pf->pvar->name)
>>>> pf->tvar->name = strdup(pf->pvar->name);
>>>> --
>>>> 1.8.3.4

2015-08-26 13:32:41

by Arnaldo Carvalho de Melo

Subject: Re: [PATCH 2/2] perf probe: Support probing at absolute address

Em Wed, Aug 26, 2015 at 09:19:27PM +0800, Wangnan (F) escreveu:
> On 2015/8/26 21:02, [email protected] wrote:
> >Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
> >>On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
> >>>>From: Wang Nan [mailto:[email protected]]
> >>>> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> >>>Why do we need "+" for the absolute address?
> >>>It seems that we can do it if we find that the given probe point
> >>>starts with "0x".

> >>I will change 2/2 as you suggestion.

> >>However, we can only ensure that in kernel side symbol never leading
> >>with '0x'. Although I don't think symbol leading with 0x is useful,
> >>it is still possible for a userspace program compiled and linked by
> >>a language other than C produces such symbol. '+' helps us separate
> >>address and function name semantically, make us don't rely on assumption
> >>on function names. If in future we do meet '0x' symbols, I think we still
> >>need the '+' syntax back. But we can do it at that time.

> >Agreed, I also think that using '+' is better, but will not dwell on
> >this so as to make progress :-)

> Maybe we should support both of them, making '+0x1234' the core
> syntax, and '0x1234' style as a syntax sugar. However I have worked
> on this problem for nearly a full day but my main work should be BPF
> related things...

> Since Masami has acked all of the 6 v3 patches, if we still need '+' I can
> bring it back with a new patch when I have time. However, same to you,
> I don't think this should be a blocking problem.

Agreed, we don't have to agree on everything all the time, lets keep
Masami happy this time :-)

- Arnaldo

2015-08-28 06:41:24

by tip-bot for Vasyl Gomonovych

Subject: [tip:perf/core] perf probe: Prevent segfault when reading probe point with absolute address

Commit-ID: e486367f0101d43a044404ed2fa35aa043b19667
Gitweb: http://git.kernel.org/tip/e486367f0101d43a044404ed2fa35aa043b19667
Author: Wang Nan <[email protected]>
AuthorDate: Tue, 25 Aug 2015 13:27:35 +0000
Committer: Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Wed, 26 Aug 2015 10:34:11 -0300

perf probe: Prevent segfault when reading probe point with absolute address

'perf probe -l' panic if there is a manually inserted probing point with
absolute address. For example:

# echo 'p:probe/abs_ffffffff811e6615 0xffffffff811e6615' > /sys/kernel/debug/tracing/kprobe_events
# perf probe -l
Segmentation fault (core dumped)

This patch fix this problem by considering the situation that
"tp->symbol == NULL" in find_perf_probe_point_from_dwarf() and
find_perf_probe_point_from_map().

After this patch:

# perf probe -l
probe:abs_ffffffff811e6615 (on SyS_write+5@fs/read_write.c)

And when debug info is missing:

# rm -rf ~/.debug
# mv /lib/modules/4.2.0-rc1+/build/vmlinux /lib/modules/4.2.0-rc1+/build/vmlinux.bak
# perf probe -l
probe:abs_ffffffff811e6615 (on sys_write+5)

Signed-off-by: Wang Nan <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Acked-by: Masami Hiramatsu <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>
---
tools/perf/util/probe-event.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index f07374b..6c7e538 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -515,7 +515,7 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
if (ret < 0)
goto error;
addr += stext;
- } else {
+ } else if (tp->symbol) {
addr = kernel_get_symbol_address_by_name(tp->symbol, false);
if (addr == 0)
goto error;
@@ -1815,17 +1815,17 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
{
struct symbol *sym = NULL;
struct map *map;
- u64 addr;
+ u64 addr = tp->address;
int ret = -ENOENT;

if (!is_kprobe) {
map = dso__new_map(tp->module);
if (!map)
goto out;
- addr = tp->address;
sym = map__find_symbol(map, addr, NULL);
} else {
- addr = kernel_get_symbol_address_by_name(tp->symbol, true);
+ if (tp->symbol)
+ addr = kernel_get_symbol_address_by_name(tp->symbol, true);
if (addr) {
addr += tp->offset;
sym = __find_kernel_function(addr, &map);