Subject: Re: [PATCH v2 2/2] perf probe: add sdt probes arguments into the
 uprobe cmd string
To: Alexis Berlemont <alexis.berlemont@gmail.com>,
        linux-kernel@vger.kernel.org
References: <20161118235637.21651-1-alexis.berlemont@gmail.com>
 <20161118235637.21651-3-alexis.berlemont@gmail.com>
Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org,
        alexander.shishkin@linux.intel.com
From: Hemant Kumar <hemant@linux.vnet.ibm.com>
Date: Mon, 21 Nov 2016 15:55:06 +0530
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Hi Alexis,

On 11/19/2016 05:26 AM, Alexis Berlemont wrote:
> An sdt probe can be associated with arguments but they were not passed
> to the user probe tracing interface (uprobe_events); this patch adapts
> the sdt argument descriptors according to the uprobe input format.
>
> As the uprobe parser does not support scaled address mode, perf will
> skip arguments which cannot be adapted to the uprobe format.
>
> Here are the results:
>
> $ perf buildid-cache -v --add test_sdt
> $ perf probe -x test_sdt sdt_libfoo:table_frob

Working for some binaries and not working for others. On some digging, I 
think, this patchset doesn't take care of the offset sign. So, when we 
try to probe with these patches applied :

# ./perf probe -x /lib64/libpthread.so.0 sdt_libpthread:pthread_start

Failed to write event: Invalid argument
   Error: Failed to add events.

With -v, the string to be written in uprobe_events is shown as :
...
Writing event: p:sdt_libpthread/pthread_start 
/usr/lib64/libpthread-2.23.so:0x75b8 arg0=%ax:u64 arg1=1600(%ax):u64 
arg2=1608(%ax):u64
...

The offsets mentioned in the string, for e.g., arg1=1600(%ax):u64 (to be 
written into the uprobe_events file don't have any sign. That is the 
issue here, i.e, we need to have a sign before the offsets.

This works fine :

# echo "p:sdt_libpthread/pthread_start 
/usr/lib64/libpthread-2.23.so:0x75b8 arg0=%ax:u64 arg1=+1600(%ax):u64 
arg2=+1608(%ax):u64" > /sys/kernel/debug/tracing/uprobe_events

For the negative offsets, i.e., '-' sign before the offsets, this works 
fine because, it takes the sign as is.

So, we need to explicitly mention the offset sign.

--
Thanks,
Hemant Kumar

> $ perf probe -x test_sdt sdt_libfoo:table_diddle
> $ perf record -e sdt_libfoo:table_frob -e sdt_libfoo:table_diddle test_sdt
> $ perf script
> test_sdt  ...   666.255678:   sdt_libfoo:table_frob: (4004d7) arg0=0 arg1=0
> test_sdt  ...   666.255683: sdt_libfoo:table_diddle: (40051a) arg0=0 arg1=0
> test_sdt  ...   666.255686:   sdt_libfoo:table_frob: (4004d7) arg0=1 arg1=2
> test_sdt  ...   666.255689: sdt_libfoo:table_diddle: (40051a) arg0=3 arg1=4
> test_sdt  ...   666.255692:   sdt_libfoo:table_frob: (4004d7) arg0=2 arg1=4
> test_sdt  ...   666.255694: sdt_libfoo:table_diddle: (40051a) arg0=6 arg1=8
>
> Signed-off-by: Alexis Berlemont <alexis.berlemont@gmail.com>
> ---
>   tools/perf/arch/x86/util/perf_regs.c |  18 +++++
>   tools/perf/util/perf_regs.c          |   4 +
>   tools/perf/util/perf_regs.h          |  13 ++++
>   tools/perf/util/probe-file.c         | 141 ++++++++++++++++++++++++++++++++++-
>   4 files changed, 172 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/arch/x86/util/perf_regs.c b/tools/perf/arch/x86/util/perf_regs.c
> index c5db14f..52a1e65 100644
> --- a/tools/perf/arch/x86/util/perf_regs.c
> +++ b/tools/perf/arch/x86/util/perf_regs.c
> @@ -26,3 +26,21 @@ const struct sample_reg sample_reg_masks[] = {
>   #endif
>   	SMPL_REG_END
>   };
> +
> +const struct sdt_name_reg sdt_reg_renamings[] = {
> +	SDT_NAME_REG(eax, ax),
> +	SDT_NAME_REG(rax, ax),
> +	SDT_NAME_REG(ebx, bx),
> +	SDT_NAME_REG(rbx, bx),
> +	SDT_NAME_REG(ecx, cx),
> +	SDT_NAME_REG(rcx, cx),
> +	SDT_NAME_REG(edx, dx),
> +	SDT_NAME_REG(rdx, dx),
> +	SDT_NAME_REG(esi, si),
> +	SDT_NAME_REG(rsi, si),
> +	SDT_NAME_REG(edi, di),
> +	SDT_NAME_REG(rdi, di),
> +	SDT_NAME_REG(ebp, bp),
> +	SDT_NAME_REG(rbp, bp),
> +	SDT_NAME_REG_END,
> +};
> diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c
> index c4023f2..1c21150 100644
> --- a/tools/perf/util/perf_regs.c
> +++ b/tools/perf/util/perf_regs.c
> @@ -6,6 +6,10 @@ const struct sample_reg __weak sample_reg_masks[] = {
>   	SMPL_REG_END
>   };
>
> +const struct sdt_name_reg __weak sdt_reg_renamings[] = {
> +	SDT_NAME_REG_END,
> +};
> +
>   #ifdef HAVE_PERF_REGS_SUPPORT
>   int perf_reg_value(u64 *valp, struct regs_dump *regs, int id)
>   {
> diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h
> index 679d6e4..41815ca 100644
> --- a/tools/perf/util/perf_regs.h
> +++ b/tools/perf/util/perf_regs.h
> @@ -15,6 +15,19 @@ struct sample_reg {
>
>   extern const struct sample_reg sample_reg_masks[];
>
> +struct sdt_name_reg {
> +	const char *sdt_name;
> +	const char *uprobe_name;
> +};
> +#define SDT_NAME_REG(n, m) {.sdt_name = "%" #n, .uprobe_name = "%" #m}
> +#define SDT_NAME_REG_END {.sdt_name = NULL, .uprobe_name = NULL}
> +
> +/*
> + * The table sdt_reg_renamings is used for adjusting gcc/gas-generated
> + * registers before filling the uprobe tracer interface.
> + */
> +extern const struct sdt_name_reg sdt_reg_renamings[];
> +
>   #ifdef HAVE_PERF_REGS_SUPPORT
>   #include <perf_regs.h>
>
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 436b647..587763d 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -27,6 +27,7 @@
>   #include "probe-event.h"
>   #include "probe-file.h"
>   #include "session.h"
> +#include "perf_regs.h"
>
>   #define MAX_CMDLEN 256
>
> @@ -687,6 +688,137 @@ static unsigned long long sdt_note__get_addr(struct sdt_note *note)
>   		 : (unsigned long long)note->addr.a64[0];
>   }
>
> +static const char * const type_to_suffix[] = {
> +	":s64", "", "", "", ":s32", "", ":s16", ":s8",
> +	"", ":u8", ":u16", "", ":u32", "", "", "", ":u64"
> +};
> +
> +static int synthesize_sdt_probe_arg(struct strbuf *buf, int i, const char *arg)
> +{
> +	const struct sdt_name_reg *rnames;
> +	char *tmp, *desc = strdup(arg);
> +	const char *suffix = "";
> +	int ret = -1;
> +
> +	if (desc == NULL) {
> +		pr_debug4("Allocation error\n");
> +		return ret;
> +	}
> +
> +	/*
> +	 * The uprobe tracer format does not support all the
> +	 * addressing modes (notably: in x86 the scaled mode); so, we
> +	 * detect ',' characters, if there is just one, there is no
> +	 * use converting the sdt arg into a uprobe one.
> +	 */
> +	if (strchr(desc, ',')) {
> +		pr_debug4("SDT argument format not supported\n");
> +		goto out;
> +	}
> +
> +	tmp = strchr(desc, '@');
> +	if (tmp) {
> +		long type_idx;
> +		/*
> +		 * Isolate the string number and convert it into a
> +		 * binary value; this will be an index to get suffix
> +		 * of the uprobe name (defining the type)
> +		 */
> +		tmp[0] = '\0';
> +		type_idx = strtol(desc, NULL, 10);
> +		if (type_idx == LONG_MIN ||
> +			type_idx == LONG_MAX) {
> +			pr_debug4("Failed to get sdt type\n");
> +			goto error;
> +		}
> +		suffix = type_to_suffix[type_idx + 8];
> +		/* Get rid of the sdt prefix which is now useless */
> +		tmp++;
> +		memmove(desc, tmp, strlen(tmp) + 1);
> +	}
> +
> +	/*
> +	 * The uprobe parser does not support all gas register names;
> +	 * so, we have to replace them (ex. for x86_64: %rax -> %ax);
> +	 * the loop below performs all the needed renamings if needed.
> +	 */
> +
> +	for (rnames = sdt_reg_renamings; rnames->sdt_name != NULL; rnames++) {
> +		char *new_desc, *sdt_name;
> +		size_t prefix_len, uprobe_len, mid_ofs, desc_len;
> +
> +		sdt_name = strstr(desc, rnames->sdt_name);
> +		if (sdt_name == NULL)
> +			continue;
> +
> +		new_desc = zalloc(strlen(desc) + 1 +
> +				strlen(rnames->uprobe_name) -
> +				strlen(rnames->sdt_name));
> +		if (new_desc == NULL)
> +			goto error;
> +
> +		prefix_len = sdt_name - desc;
> +		if (prefix_len != 0)
> +			memcpy(new_desc, desc, prefix_len);
> +
> +		uprobe_len = strlen(rnames->uprobe_name);
> +		memcpy(new_desc + prefix_len, rnames->uprobe_name, uprobe_len);
> +
> +		mid_ofs = prefix_len + strlen(rnames->sdt_name);
> +		desc_len = strlen(desc);
> +		if (mid_ofs < desc_len)
> +			memcpy(new_desc + prefix_len + uprobe_len,
> +				desc + mid_ofs, desc_len - mid_ofs);
> +
> +		free(desc);
> +		desc = new_desc;
> +	}
> +
> +	if (strbuf_addf(buf, " arg%d=%s%s", i, desc, suffix) < 0)
> +		goto error;
> +
> +out:
> +	ret = 0;
> +error:
> +	free(desc);
> +	return ret;
> +}
> +
> +static char *synthesize_sdt_probe_command(struct sdt_note *note,
> +					const char *pathname,
> +					const char *sdtgrp)
> +{
> +	struct strbuf buf;
> +	char *ret = NULL, **args;
> +	int i, args_count;
> +
> +	if (strbuf_init(&buf, 32) < 0)
> +		return NULL;
> +
> +	if (strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
> +				sdtgrp, note->name, pathname,
> +				sdt_note__get_addr(note)) < 0)
> +		goto error;
> +
> +	if (!note->args)
> +		goto out;
> +
> +	if (note->args) {
> +		args = argv_split(note->args, &args_count);
> +
> +		for (i = 0; i < args_count; ++i) {
> +			if (synthesize_sdt_probe_arg(&buf, i, args[i]) < 0)
> +				goto error;
> +		}
> +	}
> +
> +out:
> +	ret = strbuf_detach(&buf, NULL);
> +error:
> +	strbuf_release(&buf);
> +	return ret;
> +}
> +
>   int probe_cache__scan_sdt(struct probe_cache *pcache, const char *pathname)
>   {
>   	struct probe_cache_entry *entry = NULL;
> @@ -723,11 +855,12 @@ int probe_cache__scan_sdt(struct probe_cache *pcache, const char *pathname)
>   			entry->pev.group = strdup(sdtgrp);
>   			list_add_tail(&entry->node, &pcache->entries);
>   		}
> -		ret = asprintf(&buf, "p:%s/%s %s:0x%llx",
> -				sdtgrp, note->name, pathname,
> -				sdt_note__get_addr(note));
> -		if (ret < 0)
> +		buf = synthesize_sdt_probe_command(note, pathname, sdtgrp);
> +		if (!buf) {
> +			ret = -ENOMEM;
>   			break;
> +		}
> +
>   		strlist__add(entry->tevlist, buf);
>   		free(buf);
>   		entry = NULL;