Re: libdw dwarf unwind issue

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Dec 02, 2020 at 11:06:46AM +0100, Jan Kratochvil wrote:
> On Tue, 01 Dec 2020 20:41:16 +0100, Jiri Olsa wrote:
> > the fix is working for me, would you mind send full patch?
> > or just provide me with changelog and I can do it for you
> 
> I am not proficient with all the meta-tags there, I make no copyright claims
> to this patch.
> 
> 
> Regards,
> Jan

> perf libdw: Fix separte debug info files
> 
> elfutils needs to be provided main binary and separate debug info file
> respectively. Providing separate debug info file instead of the main binary is
> not sufficient.
> 
> One needs to try both supplied filename and its possible cache by its build-id
> depending on the use case.

it's great, I'll just add your's SOB if that's ok:

Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>

thanks,
jirka

> 
> diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> index 7a3dbc259cec..0ada907c60d4 100644
> --- a/tools/perf/util/unwind-libdw.c
> +++ b/tools/perf/util/unwind-libdw.c
> @@ -20,10 +20,24 @@
>  
>  static char *debuginfo_path;
>  
> +static int __find_debuginfo(Dwfl_Module *mod __maybe_unused, void **userdata,
> +			    const char *modname __maybe_unused, Dwarf_Addr base __maybe_unused,
> +			    const char *file_name, const char *debuglink_file __maybe_unused,
> +			    GElf_Word debuglink_crc __maybe_unused, char **debuginfo_file_name)
> +{
> +	const struct dso *dso = *userdata;
> +
> +	assert(dso);
> +	if (dso->symsrc_filename && strcmp (file_name, dso->symsrc_filename))
> +		*debuginfo_file_name = strdup(dso->symsrc_filename);
> +	return -1;
> +}
> +
>  static const Dwfl_Callbacks offline_callbacks = {
> -	.find_debuginfo		= dwfl_standard_find_debuginfo,
> +	.find_debuginfo		= __find_debuginfo,
>  	.debuginfo_path		= &debuginfo_path,
>  	.section_address	= dwfl_offline_section_address,
> +	// .find_elf is not set as we use dwfl_report_elf() instead.
>  };
>  
>  static int __report_module(struct addr_location *al, u64 ip,
> @@ -46,16 +60,24 @@ static int __report_module(struct addr_location *al, u64 ip,
>  	mod = dwfl_addrmodule(ui->dwfl, ip);
>  	if (mod) {
>  		Dwarf_Addr s;
> +		void **userdatap;
>  
> -		dwfl_module_info(mod, NULL, &s, NULL, NULL, NULL, NULL, NULL);
> +		dwfl_module_info(mod, &userdatap, &s, NULL, NULL, NULL, NULL, NULL);
> +		*userdatap = dso;
>  		if (s != al->map->start - al->map->pgoff)
>  			mod = 0;
>  	}
>  
>  	if (!mod)
> -		mod = dwfl_report_elf(ui->dwfl, dso->short_name,
> -				      (dso->symsrc_filename ? dso->symsrc_filename : dso->long_name), -1, al->map->start - al->map->pgoff,
> -				      false);
> +		mod = dwfl_report_elf(ui->dwfl, dso->short_name, dso->long_name, -1,
> +				      al->map->start - al->map->pgoff, false);
> +	if (!mod) {
> +		char filename[PATH_MAX];
> +
> +		if (dso__build_id_filename(dso, filename, sizeof(filename), false))
> +			mod = dwfl_report_elf(ui->dwfl, dso->short_name, filename, -1,
> +					      al->map->start - al->map->pgoff, false);
> +	}
>  
>  	return mod && dwfl_addrmodule(ui->dwfl, ip) == mod ? 0 : -1;
>  }