Subject: Re: [PATCH v2 4/5] perf-probe: Find versioned symbols from map
To: Masami Hiramatsu <mhiramat@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: bhargavb <bhargavaramudu@gmail.com>, linux-kernel@vger.kernel.org,
        Paul Clarke <pc@us.ibm.com>,
        Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>,
        linux-rt-users@vger.kernel.org, linux-perf-users@vger.kernel.org
References: <151263115609.13843.6362262297053841418.stgit@devbox>
 <151263128603.13843.14383703750561651246.stgit@devbox>
From: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Organization: IBM LTC
Date: Fri, 8 Dec 2017 12:08:41 +0100
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On 12/07/2017 08:21 AM, Masami Hiramatsu wrote:
> Find versioned symbols correctly from map.
> Commit d80406453ad4 ("perf symbols: Allow user probes on
> versioned symbols") allows user to find default versioned
> symbols (with "@@") in map. However, it did not enable
> normal versioned symbol (with "@") for perf-probe.
> E.g.
> 
>   =====
>   # ./perf probe -x /lib64/libc-2.25.so malloc_get_state
>   Failed to find symbol malloc_get_state in /usr/lib64/libc-2.25.so
>     Error: Failed to add events.
>   =====
> 
> This solves above issue by improving perf-probe symbol
> search function, as below.
> 
>   =====
>   # ./perf probe -x /lib64/libc-2.25.so malloc_get_state
>   Added new event:
>     probe_libc:malloc_get_state (on malloc_get_state in /usr/lib64/libc-2.25.so)
> 
>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe_libc:malloc_get_state -aR sleep 1
> 
>   # ./perf probe -l
>     probe_libc:malloc_get_state (on malloc_get_state@GLIBC_2.2.5 in /usr/lib64/libc-2.25.so)
>   =====
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
>  tools/perf/arch/powerpc/util/sym-handling.c |    8 ++++++++
>  tools/perf/util/probe-event.c               |   16 +++++++++++++++-
>  tools/perf/util/symbol.c                    |    5 +++++
>  tools/perf/util/symbol.h                    |    1 +
>  4 files changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/arch/powerpc/util/sym-handling.c b/tools/perf/arch/powerpc/util/sym-handling.c
> index 9c4e23d8c8ce..a3613c8d97b6 100644
> --- a/tools/perf/arch/powerpc/util/sym-handling.c
> +++ b/tools/perf/arch/powerpc/util/sym-handling.c
> @@ -64,6 +64,14 @@ int arch__compare_symbol_names_n(const char *namea, const char *nameb,
> 
>  	return strncmp(namea, nameb, n);
>  }
> +
> +const char *arch__normalize_symbol_name(const char *name)
> +{
> +	/* Skip over initial dot */
> +	if (*name == '.')
> +		name++;
> +	return name;
> +}
>  #endif
> 
>  #if defined(_CALL_ELF) && _CALL_ELF == 2
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 959c4d2ef455..94acc5846e2a 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2801,16 +2801,30 @@ static int find_probe_functions(struct map *map, char *name,
>  	int found = 0;
>  	struct symbol *sym;
>  	struct rb_node *tmp;
> +	const char *norm, *ver;
> +	char *buf = NULL;
> 
>  	if (map__load(map) < 0)
>  		return 0;
> 
>  	map__for_each_symbol(map, sym, tmp) {
> -		if (strglobmatch(sym->name, name)) {
> +		norm = arch__normalize_symbol_name(sym->name);

The weak default function arch__normalize_symbol_name() simply returns
its parameter, so norm can be a NULL ptr when parameter sym->name is a 
NULL pointer.
However when sym->name is a NULL pointer (or can be one) then the
Powerpc version of arch__normalize_symbol_name() dereferences a NULL
ptr (by checking the symbol's first character is a '.').

> +		if (!norm)
> +			continue;
> +
> +		/* We don't care about default symbol or not */
> +		ver = strchr(norm, '@');
> +		if (ver) {
> +			buf = strndup(norm, ver - norm);
> +			norm = buf;

if strndup() returns a NULL pointer (due to lack of memory)
then variable norm is a NULL ptr and strglobmatch() --> __match_glob()
derefenences that NULL pointer (1. parameter).

> +		}
> +		if (strglobmatch(norm, name)) {
>  			found++;
>  			if (syms && found < probe_conf.max_probes)
>  				syms[found - 1] = sym;
>  		}
> +		if (buf)
> +			zfree(&buf);
>  	}
> 
>  	return found;
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 1b67a8639dfe..cc065d4bfafc 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -94,6 +94,11 @@ static int prefix_underscores_count(const char *str)
>  	return tail - str;
>  }
> 
> +const char * __weak arch__normalize_symbol_name(const char *name)
> +{
> +	return name;
> +}
> +
>  int __weak arch__compare_symbol_names(const char *namea, const char *nameb)
>  {
>  	return strcmp(namea, nameb);
> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
> index a4f0075b4e5c..0563f33c1eb3 100644
> --- a/tools/perf/util/symbol.h
> +++ b/tools/perf/util/symbol.h
> @@ -349,6 +349,7 @@ bool elf__needs_adjust_symbols(GElf_Ehdr ehdr);
>  void arch__sym_update(struct symbol *s, GElf_Sym *sym);
>  #endif
> 
> +const char *arch__normalize_symbol_name(const char *name);
>  #define SYMBOL_A 0
>  #define SYMBOL_B 1
> 
> 
> --
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> 


-- 
Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany
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