Re: [PATCH v2] Allow user probes on versioned symbols

[Masami Hiramatsu]

On Thu, 30 Mar 2017 12:00:33 -0500
Paul Clarke <pc@xxxxxxxxxx> wrote:

> Symbol versioning, as in glibc, results in symbols being defined as:
> <real symbol>@[@]<version>
> (Note that "@@" identifies a default symbol, in case the symbol name
> is repeated.)
> 
> perf is currently unable to deal with this, and is unable to create
> user probes at such symbols:
> --
> $ nm /lib/powerpc64le-linux-gnu/libpthread.so.0 | grep pthread_create
> 0000000000008d30 t __pthread_create_2_1
> 0000000000008d30 T pthread_create@@GLIBC_2.17
> $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
> probe-definition(0): pthread_create
> symbol:pthread_create file:(null) line:0 offset:0 return:0 lazy:(null)
> 0 arguments
> Open Debuginfo file: /usr/lib/debug/lib/powerpc64le-linux-gnu/libpthread-2.19.so
> Try to find probe point from debuginfo.
> Probe point 'pthread_create' not found.
>     Error: Failed to add events. Reason: No such file or directory (Code: -2)
> --
> 
> One is not able to specify the fully versioned symbol, either, due to
> syntactic conflicts with other uses of "@" by perf:
> --
> $ /usr/bin/sudo perf probe -v -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create@@GLIBC_2.17
> probe-definition(0): pthread_create@@GLIBC_2.17
> Semantic error :SRC@SRC is not allowed.
> 0 arguments
>     Error: Command Parse Error. Reason: Invalid argument (Code: -22)
> --
> 
> The attached patch ignores versioning for default symbols, thus
> allowing probes to be created for these symbols:
> --
> $ /usr/bin/sudo ./perf probe -x /lib/powerpc64le-linux-gnu/libpthread.so.0 pthread_create
> Added new event:
>     probe_libpthread:pthread_create (on pthread_create in /lib/powerpc64le-linux-gnu/libpthread-2.19.so)
> 
> You can now use it in all perf tools, such as:
> 
>           perf record -e probe_libpthread:pthread_create -aR sleep 1
> 
> $ /usr/bin/sudo ./perf record -e probe_libpthread:pthread_create -aR ./test 2
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.052 MB perf.data (2 samples) ]
> $ /usr/bin/sudo ./perf script
>               test  2915 [000] 19124.260729: probe_libpthread:pthread_create: (3fff99248d38)
>               test  2916 [000] 19124.260962: probe_libpthread:pthread_create: (3fff99248d38)
> $ /usr/bin/sudo ./perf probe --del=probe_libpthread:pthread_create
> Removed event: probe_libpthread:pthread_create
> --
> 

The wrapper function name may be concerned since "map__*" is usually
used as a method for struct map. However, as c++ or other object-oriented
langages support, I think this case is considered as a namespace(e.g. 
map::compare_symbol_names() ), since this comparation is applicable only
for symbol name in map.
I'm OK for this name.

Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

Thank you,


> Signed-off-by: Paul A. Clarke <pc@xxxxxxxxxx>
> ---
> Changes in v2:
> - move logic from arch__compare_symbol_names to new map__compare_symbol_names
> - call through from map__compare_symbol_names to arch__compare_symbol_names
> - redirect uses of arch__compare_symbol_names
> - send patch to LKML
> 
>   tools/perf/util/auxtrace.c |  2 +-
>   tools/perf/util/map.c      | 21 +++++++++++++++++++++
>   tools/perf/util/map.h      |  3 ++-
>   tools/perf/util/symbol.c   |  4 ++--
>   4 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> index c5a6e0b1..f3511a6 100644
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c
> @@ -1875,7 +1875,7 @@ static bool dso_sym_match(struct symbol *sym, const char *name, int *cnt,
>   			  int idx)
>   {
>   	/* Same name, and global or the n'th found or any */
> -	return !arch__compare_symbol_names(name, sym->name) &&
> +	return !map__compare_symbol_names(name, sym->name) &&
>   	       ((!idx && sym->binding == STB_GLOBAL) ||
>   		(idx > 0 && ++*cnt == idx) ||
>   		idx < 0);
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index 4f9a71c..90342ee 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -330,6 +330,27 @@ int __weak arch__compare_symbol_names(const char *namea, const char *nameb)
>   	return strcmp(namea, nameb);
>   }
>   
> +int map__compare_symbol_names(const char *namea, const char *nameb)
> +{
> +	int rc;
> +	const char *namea_versioning, *nameb_versioning;
> +
> +	namea_versioning = strstr(namea,"@@");
> +	if (namea_versioning)
> +		namea = strndup(namea,namea_versioning-namea);
> +
> +	nameb_versioning = strstr(nameb,"@@");
> +	if (nameb_versioning)
> +		nameb = strndup(nameb,nameb_versioning-nameb);
> +
> +	rc = arch__compare_symbol_names(namea, nameb);
> +
> +	if (namea_versioning) free((void *)namea);
> +	if (nameb_versioning) free((void *)nameb);
> +
> +	return rc;
> +}
> +
>   struct symbol *map__find_symbol(struct map *map, u64 addr)
>   {
>   	if (map__load(map) < 0)
> diff --git a/tools/perf/util/map.h b/tools/perf/util/map.h
> index abdacf8..aaad64d 100644
> --- a/tools/perf/util/map.h
> +++ b/tools/perf/util/map.h
> @@ -130,13 +130,14 @@ struct thread;
>    */
>   #define __map__for_each_symbol_by_name(map, sym_name, pos)	\
>   	for (pos = map__find_symbol_by_name(map, sym_name);	\
> -	     pos && arch__compare_symbol_names(pos->name, sym_name) == 0;	\
> +	     pos && map__compare_symbol_names(pos->name, sym_name) == 0;	\
>   	     pos = symbol__next_by_name(pos))
>   
>   #define map__for_each_symbol_by_name(map, sym_name, pos)		\
>   	__map__for_each_symbol_by_name(map, sym_name, (pos))
>   
>   int arch__compare_symbol_names(const char *namea, const char *nameb);
> +int map__compare_symbol_names(const char *namea, const char *nameb);
>   void map__init(struct map *map, enum map_type type,
>   	       u64 start, u64 end, u64 pgoff, struct dso *dso);
>   struct map *map__new(struct machine *machine, u64 start, u64 len,
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index dc93940..4fb9d275 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -411,7 +411,7 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
>   		int cmp;
>   
>   		s = rb_entry(n, struct symbol_name_rb_node, rb_node);
> -		cmp = arch__compare_symbol_names(name, s->sym.name);
> +		cmp = map__compare_symbol_names(name, s->sym.name);
>   
>   		if (cmp < 0)
>   			n = n->rb_left;
> @@ -429,7 +429,7 @@ static struct symbol *symbols__find_by_name(struct rb_root *symbols,
>   		struct symbol_name_rb_node *tmp;
>   
>   		tmp = rb_entry(n, struct symbol_name_rb_node, rb_node);
> -		if (arch__compare_symbol_names(tmp->sym.name, s->sym.name))
> +		if (map__compare_symbol_names(tmp->sym.name, s->sym.name))
>   			break;
>   
>   		s = tmp;
> -- 
> 2.1.4
> 
> Regards,
> Paul Clarke
> 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>