Re: [PATCH] perf symbols: Demangle symbols for synthesized @plt entries.

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Tue, Aug 30, 2016 at 01:41:02PM +0200, Milian Wolff escreveu:
> The symbols in the synthesized @plt entries where not demangled
> before, i.e. we could end up with entries such as:

Thanks, applied.

Please CC linux-kernel@vger.kernel.org for wider exposure, as there are
many perf users (and developers) that don't subscribe to this list.

- Arnaldo
 
>     $ perf report
>     Samples: 7K of event 'cycles:ppp', Event count (approx.): 6223833141
>     Children      Self  Command          Shared Object           Symbol
>     -   93.63%    28.89%  lab_mandelbrot   lab_mandelbrot        [.] main
>         - 73.81% main
>             - 33.57% hypot
>               27.76% __hypot_finite
>               15.97% __muldc3
>                2.90% __muldc3@plt
>                2.40% _ZNK6QImage6heightEv@plt
>              + 2.14% QColor::rgb
>                1.94% _ZNK6QImage5widthEv@plt
>                1.92% cabs@plt
> 
> This patch remedies this issue by also applying demangling to the
> synthesized symbols. The output for the above is now:
> 
>     $ perf report
>     Samples: 7K of event 'cycles:ppp', Event count (approx.): 6223833141
>     Children      Self  Command          Shared Object           Symbol
>     -   93.63%    28.89%  lab_mandelbrot   lab_mandelbrot        [.] main
>         - 73.81% main
>             - 33.57% hypot
>               27.76% __hypot_finite
>               15.97% __muldc3
>                2.90% __muldc3@plt
>                2.40% QImage::height() const@plt
>              + 2.14% QColor::rgb
>                1.94% QImage::width() const@plt
>                1.92% cabs@plt
> 
> Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
> 
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> ---
>  tools/perf/util/symbol-elf.c | 81 ++++++++++++++++++++++++++++----------------
>  1 file changed, 52 insertions(+), 29 deletions(-)
> 
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index a811c13..fbe31ef 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -206,6 +206,37 @@ Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
>  	return NULL;
>  }
>  
> +static bool want_demangle(bool is_kernel_sym)
> +{
> +	return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
> +}
> +
> +static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
> +{
> +	int demangle_flags = verbose ? (DMGL_PARAMS | DMGL_ANSI) : DMGL_NO_OPTS;
> +	char *demangled = NULL;
> +
> +	/*
> +	 * We need to figure out if the object was created from C++ sources
> +	 * DWARF DW_compile_unit has this, but we don't always have access
> +	 * to it...
> +	 */
> +	if (!want_demangle(dso->kernel || kmodule))
> +	    return demangled;
> +
> +	demangled = bfd_demangle(NULL, elf_name, demangle_flags);
> +	if (demangled == NULL)
> +		demangled = java_demangle_sym(elf_name, JAVA_DEMANGLE_NORET);
> +	else if (rust_is_mangled(demangled))
> +		/*
> +		    * Input to Rust demangling is the BFD-demangled
> +		    * name which it Rust-demangles in place.
> +		    */
> +		rust_demangle_sym(demangled);
> +
> +	return demangled;
> +}
> +
>  #define elf_section__for_each_rel(reldata, pos, pos_mem, idx, nr_entries) \
>  	for (idx = 0, pos = gelf_getrel(reldata, 0, &pos_mem); \
>  	     idx < nr_entries; \
> @@ -301,11 +332,19 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss, struct map *
>  
>  		elf_section__for_each_rela(reldata, pos, pos_mem, idx,
>  					   nr_rel_entries) {
> +			const char *elf_name = NULL;
> +			char *demangled = NULL;
>  			symidx = GELF_R_SYM(pos->r_info);
>  			plt_offset += shdr_plt.sh_entsize;
>  			gelf_getsym(syms, symidx, &sym);
> +
> +			elf_name = elf_sym__name(&sym, symstrs);
> +			demangled = demangle_sym(dso, 0, elf_name);
> +			if (demangled != NULL)
> +				elf_name = demangled;
>  			snprintf(sympltname, sizeof(sympltname),
> -				 "%s@plt", elf_sym__name(&sym, symstrs));
> +				 "%s@plt", elf_name);
> +			free(demangled);
>  
>  			f = symbol__new(plt_offset, shdr_plt.sh_entsize,
>  					STB_GLOBAL, sympltname);
> @@ -323,11 +362,19 @@ int dso__synthesize_plt_symbols(struct dso *dso, struct symsrc *ss, struct map *
>  		GElf_Rel pos_mem, *pos;
>  		elf_section__for_each_rel(reldata, pos, pos_mem, idx,
>  					  nr_rel_entries) {
> +			const char *elf_name = NULL;
> +			char *demangled = NULL;
>  			symidx = GELF_R_SYM(pos->r_info);
>  			plt_offset += shdr_plt.sh_entsize;
>  			gelf_getsym(syms, symidx, &sym);
> +
> +			elf_name = elf_sym__name(&sym, symstrs);
> +			demangled = demangle_sym(dso, 0, elf_name);
> +			if (demangled != NULL)
> +				elf_name = demangled;
>  			snprintf(sympltname, sizeof(sympltname),
> -				 "%s@plt", elf_sym__name(&sym, symstrs));
> +				 "%s@plt", elf_name);
> +			free(demangled);
>  
>  			f = symbol__new(plt_offset, shdr_plt.sh_entsize,
>  					STB_GLOBAL, sympltname);
> @@ -775,11 +822,6 @@ static u64 ref_reloc(struct kmap *kmap)
>  	return 0;
>  }
>  
> -static bool want_demangle(bool is_kernel_sym)
> -{
> -	return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
> -}
> -
>  void __weak arch__sym_update(struct symbol *s __maybe_unused,
>  		GElf_Sym *sym __maybe_unused) { }
>  
> @@ -1070,29 +1112,10 @@ int dso__load_sym(struct dso *dso, struct map *map,
>  			sym.st_value -= shdr.sh_addr - shdr.sh_offset;
>  		}
>  new_symbol:
> -		/*
> -		 * We need to figure out if the object was created from C++ sources
> -		 * DWARF DW_compile_unit has this, but we don't always have access
> -		 * to it...
> -		 */
> -		if (want_demangle(dso->kernel || kmodule)) {
> -			int demangle_flags = DMGL_NO_OPTS;
> -			if (verbose)
> -				demangle_flags = DMGL_PARAMS | DMGL_ANSI;
> -
> -			demangled = bfd_demangle(NULL, elf_name, demangle_flags);
> -			if (demangled == NULL)
> -				demangled = java_demangle_sym(elf_name, JAVA_DEMANGLE_NORET);
> -			else if (rust_is_mangled(demangled))
> -				/*
> -				 * Input to Rust demangling is the BFD-demangled
> -				 * name which it Rust-demangles in place.
> -				 */
> -				rust_demangle_sym(demangled);
> +		demangled = demangle_sym(dso, kmodule, elf_name);
> +		if (demangled != NULL)
> +			elf_name = demangled;
>  
> -			if (demangled != NULL)
> -				elf_name = demangled;
> -		}
>  		f = symbol__new(sym.st_value, sym.st_size,
>  				GELF_ST_BIND(sym.st_info), elf_name);
>  		free(demangled);
> -- 
> 2.9.3