Re: libdw dwarf unwind issue

[Jiri Olsa <jolsa@redhat.com>]

On Sat, Nov 28, 2020 at 05:07:40AM +0100, Jan Kratochvil wrote:
> On Mon, 23 Nov 2020 23:12:47 +0100, Jiri Olsa wrote:
> > it fixes the issue for me, but it breaks the dwarf test:
> > 
> > 72: DWARF unwind                                                    : FAILED!
> > [jolsa@krava perf]$ sudo ./perf test dwarf -v
> > 72: DWARF unwind                                                    :
> > --- start ---
> > test child forked, pid 2084484
> > unwind: failed with 'No such file or directory'
> > got wrong number of stack entries 0 != 8
> > test child finished with -1
> > ---- end ----
> > DWARF unwind: FAILED!
> 
> The previous patch required ~/.debug/ build-id symlink, fixed.
> 
> I hope dso->symsrc_filename is always already set if a separate debug info is
> present.

it should be the one with .symtab section

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

thanks,
jirka

> 
> 
> Jan

> diff --git a/tools/perf/util/unwind-libdw.c b/tools/perf/util/unwind-libdw.c
> index 7a3dbc259cec..400e4832b50e 100644
> --- a/tools/perf/util/unwind-libdw.c
> +++ b/tools/perf/util/unwind-libdw.c
> @@ -20,10 +20,25 @@
>  
>  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 __maybe_unused,
> +			    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)
> +		*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 +61,24 @@ 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;
>  }