Perf can add a probe on kernel module which has not been loaded yet.
Current implementation finds module name from path. But if filename
is different from actual module name then perf fails to register
probe while loading module because of mismatch in names. For example,
samples/kobject/kobject-example.ko is loaded as kobject_example.
Before applying patch:
$ sudo ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in kobject-example)
You can now use it in all perf tools, such as:
perf record -e probe:foo_show -aR sleep 1
$ cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show kobject-example:foo_show
$ insmod kobject-example.ko
$ lsmod
Module Size Used by
kobject_example 16384 0
Generate read to /sys/kernel/kobject_example/foo while recording data
with below command
$ sudo ./perf record -e probe:foo_show -a
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.093 MB perf.data ]
$./perf report --stdio -F overhead,comm,dso,sym
Error:
The perf.data.old file has no samples!
After applying patch:
$ sudo ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in kobject_example)
You can now use it in all perf tools, such as:
perf record -e probe:foo_show -aR sleep 1
$ sudo cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show kobject_example:foo_show
$ insmod kobject-example.ko
$ lsmod
Module Size Used by
kobject_example 16384 0
Generate read to /sys/kernel/kobject_example/foo while recording data
with below command
$ sudo ./perf record -e probe:foo_show -a
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.097 MB perf.data (8 samples) ]
$ sudo ./perf report --stdio -F overhead,comm,dso,sym
...
# Samples: 8 of event 'probe:foo_show'
# Event count (approx.): 8
#
# Overhead Command Shared Object Symbol
# ........ ....... ................. ............
#
100.00% cat [kobject_example] [k] foo_show
Signed-off-by: Ravi Bangoria <[email protected]>
---
tools/perf/util/probe-event.c | 78 +++++++++++++++++++++++++++++++++++--------
tools/perf/util/probe-event.h | 2 ++
2 files changed, 66 insertions(+), 14 deletions(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 8319fbb..05d0905 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
return true;
}
+/*
+ * NOTE:
+ * '.gnu.linkonce.this_module' section of kernel module elf directly
+ * maps to 'struct module' from linux/module.h. This section contains
+ * actual module name which will be used by kernel after loading it.
+ * But, we cannot use 'struct module' here since linux/module.h is not
+ * exposed to user-space. Offset of 'name' has remained same from long
+ * time, so hardcoding it here.
+ */
+#ifdef __LP64__
+#define MOD_NAME_OFFSET 24
+#else
+#define MOD_NAME_OFFSET 12
+#endif
+
+/*
+ * @module can be module name of module file path. In case of path,
+ * inspect elf and find out what is actual module name.
+ * Caller has to free mod_name after using it.
+ */
+char *find_module_name(const char *module)
+{
+ int fd;
+ Elf *elf;
+ GElf_Ehdr ehdr;
+ GElf_Shdr shdr;
+ Elf_Data *data;
+ Elf_Scn *sec;
+ char *mod_name = NULL;
+
+ fd = open(module, O_RDONLY);
+ if (fd < 0)
+ return NULL;
+
+ elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+ if (elf == NULL)
+ goto elf_err;
+
+ if (gelf_getehdr(elf, &ehdr) == NULL)
+ goto ret_err;
+
+ sec = elf_section_by_name(elf, &ehdr, &shdr,
+ ".gnu.linkonce.this_module", NULL);
+ if (!sec)
+ goto ret_err;
+
+ data = elf_getdata(sec, NULL);
+ if (!data || !data->d_buf)
+ goto ret_err;
+
+ mod_name = strdup((char *)data->d_buf + MOD_NAME_OFFSET);
+
+ret_err:
+ elf_end(elf);
+elf_err:
+ close(fd);
+ return mod_name;
+}
+
#ifdef HAVE_DWARF_SUPPORT
static int kernel_get_module_dso(const char *module, struct dso **pdso)
@@ -583,32 +642,23 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
int ntevs, const char *module)
{
int i, ret = 0;
- char *tmp;
+ char *mod_name;
if (!module)
return 0;
- tmp = strrchr(module, '/');
- if (tmp) {
- /* This is a module path -- get the module name */
- module = strdup(tmp + 1);
- if (!module)
- return -ENOMEM;
- tmp = strchr(module, '.');
- if (tmp)
- *tmp = '\0';
- tmp = (char *)module; /* For free() */
- }
+ mod_name = find_module_name(module);
for (i = 0; i < ntevs; i++) {
- tevs[i].point.module = strdup(module);
+ tevs[i].point.module =
+ strdup(mod_name ? mod_name : module);
if (!tevs[i].point.module) {
ret = -ENOMEM;
break;
}
}
- free(tmp);
+ free(mod_name);
return ret;
}
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index e54e7b0..0468fa3 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -166,4 +166,6 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
struct perf_probe_arg *pvar);
+char *find_module_name(const char *module);
+
#endif /*_PROBE_EVENT_H */
--
2.1.4
Perf is not able to register probe in kernel module when dwarf supprt
is not there(and so it goes for symtab). Perf passes full path of
module where only module name is required which is causing the problem.
This patch fixes this issue.
Before applying patch:
$ dpkg -s libdw-dev
dpkg-query: package 'libdw-dev' is not installed ...
$ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in /linux/samples/kobject/kobject-example.ko)
You can now use it in all perf tools, such as:
perf record -e probe:foo_show -aR sleep 1
$ cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show /linux/samples/kobject/kobject-example.ko:foo_show
After applying patch:
$ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
Added new event:
probe:foo_show (on foo_show in kobject_example)
You can now use it in all perf tools, such as:
perf record -e probe:foo_show -aR sleep 1
$ cat /sys/kernel/debug/tracing/kprobe_events
p:probe/foo_show kobject_example:foo_show
Signed-off-by: Ravi Bangoria <[email protected]>
---
tools/perf/util/probe-event.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 05d0905..54e6a5a 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2566,6 +2566,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
struct probe_trace_point *tp;
int num_matched_functions;
int ret, i, j, skipped = 0;
+ char *mod_name;
map = get_target_map(pev->target, pev->uprobes);
if (!map) {
@@ -2650,9 +2651,19 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
tp->realname = strdup_or_goto(sym->name, nomem_out);
tp->retprobe = pp->retprobe;
- if (pev->target)
- tev->point.module = strdup_or_goto(pev->target,
- nomem_out);
+ if (pev->target) {
+ if (pev->uprobes) {
+ tev->point.module = strdup_or_goto(pev->target,
+ nomem_out);
+ } else {
+ mod_name = find_module_name(pev->target);
+ tev->point.module =
+ strdup(mod_name ? mod_name : pev->target);
+ free(mod_name);
+ if (!tev->point.module)
+ goto nomem_out;
+ }
+ }
tev->uprobes = pev->uprobes;
tev->nargs = pev->nargs;
if (tev->nargs) {
--
2.1.4
Hi Ravi,
On Mon, 25 Apr 2016 16:08:27 +0530
Ravi Bangoria <[email protected]> wrote:
> Perf can add a probe on kernel module which has not been loaded yet.
> Current implementation finds module name from path. But if filename
> is different from actual module name then perf fails to register
> probe while loading module because of mismatch in names. For example,
> samples/kobject/kobject-example.ko is loaded as kobject_example.
Ah! right, good catch!
Have some comment below;
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 8319fbb..05d0905 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
> return true;
> }
>
> +/*
> + * NOTE:
> + * '.gnu.linkonce.this_module' section of kernel module elf directly
> + * maps to 'struct module' from linux/module.h. This section contains
> + * actual module name which will be used by kernel after loading it.
> + * But, we cannot use 'struct module' here since linux/module.h is not
> + * exposed to user-space. Offset of 'name' has remained same from long
> + * time, so hardcoding it here.
> + */
> +#ifdef __LP64__
> +#define MOD_NAME_OFFSET 24
> +#else
> +#define MOD_NAME_OFFSET 12
> +#endif
> +
> +/*
> + * @module can be module name of module file path. In case of path,
> + * inspect elf and find out what is actual module name.
> + * Caller has to free mod_name after using it.
> + */
> +char *find_module_name(const char *module)
Could you make this function static, since there is no caller outside
this file?
> +{
> + int fd;
> + Elf *elf;
> + GElf_Ehdr ehdr;
> + GElf_Shdr shdr;
> + Elf_Data *data;
> + Elf_Scn *sec;
> + char *mod_name = NULL;
> +
> + fd = open(module, O_RDONLY);
> + if (fd < 0)
> + return NULL;
> +
> + elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
> + if (elf == NULL)
> + goto elf_err;
> +
> + if (gelf_getehdr(elf, &ehdr) == NULL)
> + goto ret_err;
> +
> + sec = elf_section_by_name(elf, &ehdr, &shdr,
> + ".gnu.linkonce.this_module", NULL);
> + if (!sec)
> + goto ret_err;
> +
> + data = elf_getdata(sec, NULL);
> + if (!data || !data->d_buf)
> + goto ret_err;
> +
> + mod_name = strdup((char *)data->d_buf + MOD_NAME_OFFSET);
> +
> +ret_err:
> + elf_end(elf);
> +elf_err:
> + close(fd);
> + return mod_name;
> +}
> +
> #ifdef HAVE_DWARF_SUPPORT
>
> static int kernel_get_module_dso(const char *module, struct dso **pdso)
> @@ -583,32 +642,23 @@ static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
> int ntevs, const char *module)
> {
> int i, ret = 0;
> - char *tmp;
> + char *mod_name;
>
> if (!module)
> return 0;
>
> - tmp = strrchr(module, '/');
> - if (tmp) {
> - /* This is a module path -- get the module name */
> - module = strdup(tmp + 1);
> - if (!module)
> - return -ENOMEM;
> - tmp = strchr(module, '.');
> - if (tmp)
> - *tmp = '\0';
> - tmp = (char *)module; /* For free() */
> - }
> + mod_name = find_module_name(module);
>
> for (i = 0; i < ntevs; i++) {
> - tevs[i].point.module = strdup(module);
> + tevs[i].point.module =
> + strdup(mod_name ? mod_name : module);
> if (!tevs[i].point.module) {
> ret = -ENOMEM;
> break;
> }
> }
>
> - free(tmp);
> + free(mod_name);
> return ret;
> }
>
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index e54e7b0..0468fa3 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -166,4 +166,6 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> struct perf_probe_arg *pvar);
>
> +char *find_module_name(const char *module);
And remove this.
Others looks good to me!
Thank you,
> +
> #endif /*_PROBE_EVENT_H */
> --
> 2.1.4
>
--
Masami Hiramatsu <[email protected]>
On Mon, 25 Apr 2016 16:08:28 +0530
Ravi Bangoria <[email protected]> wrote:
> Perf is not able to register probe in kernel module when dwarf supprt
> is not there(and so it goes for symtab). Perf passes full path of
> module where only module name is required which is causing the problem.
> This patch fixes this issue.
>
> Before applying patch:
>
> $ dpkg -s libdw-dev
> dpkg-query: package 'libdw-dev' is not installed ...
>
> $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
> Added new event:
> probe:foo_show (on foo_show in /linux/samples/kobject/kobject-example.ko)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:foo_show -aR sleep 1
>
> $ cat /sys/kernel/debug/tracing/kprobe_events
> p:probe/foo_show /linux/samples/kobject/kobject-example.ko:foo_show
>
> After applying patch:
>
> $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
> Added new event:
> probe:foo_show (on foo_show in kobject_example)
>
> You can now use it in all perf tools, such as:
>
> perf record -e probe:foo_show -aR sleep 1
>
> $ cat /sys/kernel/debug/tracing/kprobe_events
> p:probe/foo_show kobject_example:foo_show
>
Looks good to me :)
However, it seems that this patch depends on your previous patch
("perf probe: Fix offline module name missmatch issue")
In that case, could you make these a series of patches?
Acked-by: Masami Hiramatsu <[email protected]>
Thanks,
> Signed-off-by: Ravi Bangoria <[email protected]>
> ---
> tools/perf/util/probe-event.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 05d0905..54e6a5a 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2566,6 +2566,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
> struct probe_trace_point *tp;
> int num_matched_functions;
> int ret, i, j, skipped = 0;
> + char *mod_name;
>
> map = get_target_map(pev->target, pev->uprobes);
> if (!map) {
> @@ -2650,9 +2651,19 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
> tp->realname = strdup_or_goto(sym->name, nomem_out);
>
> tp->retprobe = pp->retprobe;
> - if (pev->target)
> - tev->point.module = strdup_or_goto(pev->target,
> - nomem_out);
> + if (pev->target) {
> + if (pev->uprobes) {
> + tev->point.module = strdup_or_goto(pev->target,
> + nomem_out);
> + } else {
> + mod_name = find_module_name(pev->target);
> + tev->point.module =
> + strdup(mod_name ? mod_name : pev->target);
> + free(mod_name);
> + if (!tev->point.module)
> + goto nomem_out;
> + }
> + }
> tev->uprobes = pev->uprobes;
> tev->nargs = pev->nargs;
> if (tev->nargs) {
> --
> 2.1.4
>
--
Masami Hiramatsu <[email protected]>
On Tue, 26 Apr 2016 06:24:38 +0900
Masami Hiramatsu <[email protected]> wrote:
> > +/*
> > + * NOTE:
> > + * '.gnu.linkonce.this_module' section of kernel module elf directly
> > + * maps to 'struct module' from linux/module.h. This section contains
> > + * actual module name which will be used by kernel after loading it.
> > + * But, we cannot use 'struct module' here since linux/module.h is not
> > + * exposed to user-space. Offset of 'name' has remained same from long
> > + * time, so hardcoding it here.
> > + */
BTW, is there no way to get the module name avoiding to access
this "hidden" data structure?
This looks very tricky way...
Thanks,
--
Masami Hiramatsu <[email protected]>
Thanks Masami for reviewing.
Please find my replies to your comment.
On Tuesday 26 April 2016 02:54 AM, Masami Hiramatsu wrote:
> Hi Ravi,
>
> On Mon, 25 Apr 2016 16:08:27 +0530
> Ravi Bangoria <[email protected]> wrote:
>
>> Perf can add a probe on kernel module which has not been loaded yet.
>> Current implementation finds module name from path. But if filename
>> is different from actual module name then perf fails to register
>> probe while loading module because of mismatch in names. For example,
>> samples/kobject/kobject-example.ko is loaded as kobject_example.
> Ah! right, good catch!
> Have some comment below;
>
>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>> index 8319fbb..05d0905 100644
>> --- a/tools/perf/util/probe-event.c
>> +++ b/tools/perf/util/probe-event.c
>> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
>> return true;
>> }
>>
>> +/*
>> + * NOTE:
>> + * '.gnu.linkonce.this_module' section of kernel module elf directly
>> + * maps to 'struct module' from linux/module.h. This section contains
>> + * actual module name which will be used by kernel after loading it.
>> + * But, we cannot use 'struct module' here since linux/module.h is not
>> + * exposed to user-space. Offset of 'name' has remained same from long
>> + * time, so hardcoding it here.
>> + */
>> +#ifdef __LP64__
>> +#define MOD_NAME_OFFSET 24
>> +#else
>> +#define MOD_NAME_OFFSET 12
>> +#endif
>> +
>> +/*
>> + * @module can be module name of module file path. In case of path,
>> + * inspect elf and find out what is actual module name.
>> + * Caller has to free mod_name after using it.
>> + */
>> +char *find_module_name(const char *module)
> Could you make this function static, since there is no caller outside
> this file?
Yes. no caller outside of this file. But,
In this patch, function find_module_name is defined outside of
#ifdef HAVE_DWARF_SUPPORT while it's being called from inside of
#ifdef HAVE_DWARF_SUPPORT.
If I make it static and if there is no dwarf support, there will be
compilation
error about function defined but not used.
And in second patch("perf probe: Fix module probe issue if no dwarf
support"),
I'm calling it from outside of #ifdef HAVE_DWARF_SUPPORT.
So I have two options:
1. merge both the patches and make definition as static
2. make function static in second patch
I've chose second approach and sent v2. But please let me know if there is
better way to do it.
Regards,
Ravi
Thanks Masami,
On Tuesday 26 April 2016 07:49 AM, Masami Hiramatsu wrote:
> On Tue, 26 Apr 2016 06:24:38 +0900
> Masami Hiramatsu <[email protected]> wrote:
>>> +/*
>>> + * NOTE:
>>> + * '.gnu.linkonce.this_module' section of kernel module elf directly
>>> + * maps to 'struct module' from linux/module.h. This section contains
>>> + * actual module name which will be used by kernel after loading it.
>>> + * But, we cannot use 'struct module' here since linux/module.h is not
>>> + * exposed to user-space. Offset of 'name' has remained same from long
>>> + * time, so hardcoding it here.
>>> + */
> BTW, is there no way to get the module name avoiding to access
> this "hidden" data structure?
> This looks very tricky way...
So this is the same approach kernel use to find module name when module is
loaded. Please refer this function for more detail:
kernel/module.c :: static struct module *setup_load_info(...)
Regards,
Ravi
On Tuesday 26 April 2016 02:59 AM, Masami Hiramatsu wrote:
> On Mon, 25 Apr 2016 16:08:28 +0530
> Ravi Bangoria <[email protected]> wrote:
>
>> Perf is not able to register probe in kernel module when dwarf supprt
>> is not there(and so it goes for symtab). Perf passes full path of
>> module where only module name is required which is causing the problem.
>> This patch fixes this issue.
>>
>> Before applying patch:
>>
>> $ dpkg -s libdw-dev
>> dpkg-query: package 'libdw-dev' is not installed ...
>>
>> $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
>> Added new event:
>> probe:foo_show (on foo_show in /linux/samples/kobject/kobject-example.ko)
>>
>> You can now use it in all perf tools, such as:
>>
>> perf record -e probe:foo_show -aR sleep 1
>>
>> $ cat /sys/kernel/debug/tracing/kprobe_events
>> p:probe/foo_show /linux/samples/kobject/kobject-example.ko:foo_show
>>
>> After applying patch:
>>
>> $ ./perf probe -m /linux/samples/kobject/kobject-example.ko foo_show
>> Added new event:
>> probe:foo_show (on foo_show in kobject_example)
>>
>> You can now use it in all perf tools, such as:
>>
>> perf record -e probe:foo_show -aR sleep 1
>>
>> $ cat /sys/kernel/debug/tracing/kprobe_events
>> p:probe/foo_show kobject_example:foo_show
>>
> Looks good to me :)
> However, it seems that this patch depends on your previous patch
> ("perf probe: Fix offline module name missmatch issue")
> In that case, could you make these a series of patches?
>
> Acked-by: Masami Hiramatsu <[email protected]>
Thanks Masami,
I've sent v2 with changes you suggested. Please review it.
Regards,
Ravi
On 2016/4/26 16:56, Ravi Bangoria wrote:
> Thanks Masami for reviewing.
>
> Please find my replies to your comment.
>
> On Tuesday 26 April 2016 02:54 AM, Masami Hiramatsu wrote:
>> Hi Ravi,
>>
>> On Mon, 25 Apr 2016 16:08:27 +0530
>> Ravi Bangoria <[email protected]> wrote:
>>
>>> Perf can add a probe on kernel module which has not been loaded yet.
>>> Current implementation finds module name from path. But if filename
>>> is different from actual module name then perf fails to register
>>> probe while loading module because of mismatch in names. For example,
>>> samples/kobject/kobject-example.ko is loaded as kobject_example.
>> Ah! right, good catch!
>> Have some comment below;
>>
>>> diff --git a/tools/perf/util/probe-event.c
>>> b/tools/perf/util/probe-event.c
>>> index 8319fbb..05d0905 100644
>>> --- a/tools/perf/util/probe-event.c
>>> +++ b/tools/perf/util/probe-event.c
>>> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char
>>> *symbol, unsigned long address)
>>> return true;
>>> }
>>> +/*
>>> + * NOTE:
>>> + * '.gnu.linkonce.this_module' section of kernel module elf directly
>>> + * maps to 'struct module' from linux/module.h. This section contains
>>> + * actual module name which will be used by kernel after loading it.
>>> + * But, we cannot use 'struct module' here since linux/module.h is not
>>> + * exposed to user-space. Offset of 'name' has remained same from long
>>> + * time, so hardcoding it here.
>>> + */
>>> +#ifdef __LP64__
>>> +#define MOD_NAME_OFFSET 24
>>> +#else
>>> +#define MOD_NAME_OFFSET 12
>>> +#endif
>>> +
>>> +/*
>>> + * @module can be module name of module file path. In case of path,
>>> + * inspect elf and find out what is actual module name.
>>> + * Caller has to free mod_name after using it.
>>> + */
>>> +char *find_module_name(const char *module)
>> Could you make this function static, since there is no caller outside
>> this file?
>
> Yes. no caller outside of this file. But,
>
> In this patch, function find_module_name is defined outside of
> #ifdef HAVE_DWARF_SUPPORT while it's being called from inside of
> #ifdef HAVE_DWARF_SUPPORT.
>
> If I make it static and if there is no dwarf support, there will be
> compilation
> error about function defined but not used.
>
> And in second patch("perf probe: Fix module probe issue if no dwarf
> support"),
> I'm calling it from outside of #ifdef HAVE_DWARF_SUPPORT.
>
> So I have two options:
> 1. merge both the patches and make definition as static
> 2. make function static in second patch
>
> I've chose second approach and sent v2. But please let me know if
> there is
> better way to do it.
>
Try __maybe_unused directive?
Thank you.
On Tuesday 26 April 2016 02:45 PM, Wangnan (F) wrote:
>
>
> On 2016/4/26 16:56, Ravi Bangoria wrote:
>> Thanks Masami for reviewing.
>>
>> Please find my replies to your comment.
>>
>> On Tuesday 26 April 2016 02:54 AM, Masami Hiramatsu wrote:
>>> Hi Ravi,
>>>
>>> On Mon, 25 Apr 2016 16:08:27 +0530
>>> Ravi Bangoria <[email protected]> wrote:
>>>
>>>> Perf can add a probe on kernel module which has not been loaded yet.
>>>> Current implementation finds module name from path. But if filename
>>>> is different from actual module name then perf fails to register
>>>> probe while loading module because of mismatch in names. For example,
>>>> samples/kobject/kobject-example.ko is loaded as kobject_example.
>>> Ah! right, good catch!
>>> Have some comment below;
>>>
>>>> diff --git a/tools/perf/util/probe-event.c
>>>> b/tools/perf/util/probe-event.c
>>>> index 8319fbb..05d0905 100644
>>>> --- a/tools/perf/util/probe-event.c
>>>> +++ b/tools/perf/util/probe-event.c
>>>> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char
>>>> *symbol, unsigned long address)
>>>> return true;
>>>> }
>>>> +/*
>>>> + * NOTE:
>>>> + * '.gnu.linkonce.this_module' section of kernel module elf directly
>>>> + * maps to 'struct module' from linux/module.h. This section contains
>>>> + * actual module name which will be used by kernel after loading it.
>>>> + * But, we cannot use 'struct module' here since linux/module.h is
>>>> not
>>>> + * exposed to user-space. Offset of 'name' has remained same from
>>>> long
>>>> + * time, so hardcoding it here.
>>>> + */
>>>> +#ifdef __LP64__
>>>> +#define MOD_NAME_OFFSET 24
>>>> +#else
>>>> +#define MOD_NAME_OFFSET 12
>>>> +#endif
>>>> +
>>>> +/*
>>>> + * @module can be module name of module file path. In case of path,
>>>> + * inspect elf and find out what is actual module name.
>>>> + * Caller has to free mod_name after using it.
>>>> + */
>>>> +char *find_module_name(const char *module)
>>> Could you make this function static, since there is no caller outside
>>> this file?
>>
>> Yes. no caller outside of this file. But,
>>
>> In this patch, function find_module_name is defined outside of
>> #ifdef HAVE_DWARF_SUPPORT while it's being called from inside of
>> #ifdef HAVE_DWARF_SUPPORT.
>>
>> If I make it static and if there is no dwarf support, there will be
>> compilation
>> error about function defined but not used.
>>
>> And in second patch("perf probe: Fix module probe issue if no dwarf
>> support"),
>> I'm calling it from outside of #ifdef HAVE_DWARF_SUPPORT.
>>
>> So I have two options:
>> 1. merge both the patches and make definition as static
>> 2. make function static in second patch
>>
>> I've chose second approach and sent v2. But please let me know if
>> there is
>> better way to do it.
>>
>
> Try __maybe_unused directive?
>
Thanks Wangnan for suggestion,
Actually I tried to use __maybe_unused with definition of
find_module_name but
it throws following compilation error:
util/probe-event.c:289:1: error: expected ‘,’ or ‘;’ before ‘{’ token
{
^
util/probe-event.c:288:14: error: ‘find_module_name’ declared ‘static’
but never defined [-Werror=unused-function]
static char *find_module_name(const char *module) __maybe_unused
^
CC util/zlib.o
cc1: all warnings being treated as errors
I've to declare prototype of function with __maybe_unused before it's
definition to
resolve this error. And, anyway this is temporary and need to be removed
in patch 2,
I think no need to do this change.
Regards,
Ravi
On Tue, 26 Apr 2016 14:26:48 +0530
Ravi Bangoria <[email protected]> wrote:
> Thanks Masami for reviewing.
>
> Please find my replies to your comment.
>
> On Tuesday 26 April 2016 02:54 AM, Masami Hiramatsu wrote:
> > Hi Ravi,
> >
> > On Mon, 25 Apr 2016 16:08:27 +0530
> > Ravi Bangoria <[email protected]> wrote:
> >
> >> Perf can add a probe on kernel module which has not been loaded yet.
> >> Current implementation finds module name from path. But if filename
> >> is different from actual module name then perf fails to register
> >> probe while loading module because of mismatch in names. For example,
> >> samples/kobject/kobject-example.ko is loaded as kobject_example.
> > Ah! right, good catch!
> > Have some comment below;
> >
> >> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >> index 8319fbb..05d0905 100644
> >> --- a/tools/perf/util/probe-event.c
> >> +++ b/tools/perf/util/probe-event.c
> >> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
> >> return true;
> >> }
> >>
> >> +/*
> >> + * NOTE:
> >> + * '.gnu.linkonce.this_module' section of kernel module elf directly
> >> + * maps to 'struct module' from linux/module.h. This section contains
> >> + * actual module name which will be used by kernel after loading it.
> >> + * But, we cannot use 'struct module' here since linux/module.h is not
> >> + * exposed to user-space. Offset of 'name' has remained same from long
> >> + * time, so hardcoding it here.
> >> + */
> >> +#ifdef __LP64__
> >> +#define MOD_NAME_OFFSET 24
> >> +#else
> >> +#define MOD_NAME_OFFSET 12
> >> +#endif
> >> +
> >> +/*
> >> + * @module can be module name of module file path. In case of path,
> >> + * inspect elf and find out what is actual module name.
> >> + * Caller has to free mod_name after using it.
> >> + */
> >> +char *find_module_name(const char *module)
> > Could you make this function static, since there is no caller outside
> > this file?
>
> Yes. no caller outside of this file. But,
>
> In this patch, function find_module_name is defined outside of
> #ifdef HAVE_DWARF_SUPPORT while it's being called from inside of
> #ifdef HAVE_DWARF_SUPPORT.
>
> If I make it static and if there is no dwarf support, there will be
> compilation
> error about function defined but not used.
>
> And in second patch("perf probe: Fix module probe issue if no dwarf
> support"),
> I'm calling it from outside of #ifdef HAVE_DWARF_SUPPORT.
>
> So I have two options:
> 1. merge both the patches and make definition as static
> 2. make function static in second patch
>
> I've chose second approach and sent v2. But please let me know if there is
> better way to do it.
Ah, I see.
In that case, you can swap the patch in the series and move find_module_name
in the other patch ;)
Thanks!
--
Masami Hiramatsu <[email protected]>
On Tuesday 26 April 2016 04:16 PM, Masami Hiramatsu wrote:
> On Tue, 26 Apr 2016 14:26:48 +0530
> Ravi Bangoria <[email protected]> wrote:
>
>> Thanks Masami for reviewing.
>>
>> Please find my replies to your comment.
>>
>> On Tuesday 26 April 2016 02:54 AM, Masami Hiramatsu wrote:
>>> Hi Ravi,
>>>
>>> On Mon, 25 Apr 2016 16:08:27 +0530
>>> Ravi Bangoria <[email protected]> wrote:
>>>
>>>> Perf can add a probe on kernel module which has not been loaded yet.
>>>> Current implementation finds module name from path. But if filename
>>>> is different from actual module name then perf fails to register
>>>> probe while loading module because of mismatch in names. For example,
>>>> samples/kobject/kobject-example.ko is loaded as kobject_example.
>>> Ah! right, good catch!
>>> Have some comment below;
>>>
>>>> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
>>>> index 8319fbb..05d0905 100644
>>>> --- a/tools/perf/util/probe-event.c
>>>> +++ b/tools/perf/util/probe-event.c
>>>> @@ -265,6 +265,65 @@ static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
>>>> return true;
>>>> }
>>>>
>>>> +/*
>>>> + * NOTE:
>>>> + * '.gnu.linkonce.this_module' section of kernel module elf directly
>>>> + * maps to 'struct module' from linux/module.h. This section contains
>>>> + * actual module name which will be used by kernel after loading it.
>>>> + * But, we cannot use 'struct module' here since linux/module.h is not
>>>> + * exposed to user-space. Offset of 'name' has remained same from long
>>>> + * time, so hardcoding it here.
>>>> + */
>>>> +#ifdef __LP64__
>>>> +#define MOD_NAME_OFFSET 24
>>>> +#else
>>>> +#define MOD_NAME_OFFSET 12
>>>> +#endif
>>>> +
>>>> +/*
>>>> + * @module can be module name of module file path. In case of path,
>>>> + * inspect elf and find out what is actual module name.
>>>> + * Caller has to free mod_name after using it.
>>>> + */
>>>> +char *find_module_name(const char *module)
>>> Could you make this function static, since there is no caller outside
>>> this file?
>> Yes. no caller outside of this file. But,
>>
>> In this patch, function find_module_name is defined outside of
>> #ifdef HAVE_DWARF_SUPPORT while it's being called from inside of
>> #ifdef HAVE_DWARF_SUPPORT.
>>
>> If I make it static and if there is no dwarf support, there will be
>> compilation
>> error about function defined but not used.
>>
>> And in second patch("perf probe: Fix module probe issue if no dwarf
>> support"),
>> I'm calling it from outside of #ifdef HAVE_DWARF_SUPPORT.
>>
>> So I have two options:
>> 1. merge both the patches and make definition as static
>> 2. make function static in second patch
>>
>> I've chose second approach and sent v2. But please let me know if there is
>> better way to do it.
> Ah, I see.
> In that case, you can swap the patch in the series and move find_module_name
> in the other patch ;)
Thanks :) Sent patch with changes. Please review it.
Regards,
Ravi