Re: [PATCH] perf symbols: Don't apply the symfs layout to synthesised paths

[Ian Rogers]

On Mon, Aug 10, 2026 at 10:00 PM Zhan Xusheng <zhanxusheng1024@xxxxxxxxx> wrote:
>
> The flat symfs layout was implemented inside __symbol__join_symfs() alone,
> which went from
>
>         return path__join(bf, size, symbol_conf.symfs, path);
>
> to taking perf_basename(path) first.  No caller was changed, so all of them
> got it.  Most pass dso__long_name(), which is what the option is about, but
> some pass a path perf built itself:
>
>   dso.c        "/usr/lib/debug"             -> "debug"
>   dso.c        "/usr/lib/debug/.build-id/"  -> ""
>   build-id.c   "/usr/lib/debug/.build-id/"  -> ""
>   disasm.c     <file under buildid_dir>     -> last component
>
> perf_basename() yields "" for a path ending in '/'.  So with --symfs
> DIR,flat the FEDORA, UBUNTU and MIXEDUP_UBUNTU debuginfo lookups land in
> <symfs>/debug/, the two build-id ones in <symfs> itself, and disasm.c
> flattens a path under perf's own build-id cache.
>
> Use path__join() at those sites, which is what the helper did for them
> before.  A hierarchy layout is unaffected, being that same call.  The
> OPENEMBEDDED site passes "", where perf_basename() is already a no-op;
> it is converted for uniformity.  Every remaining __symbol__join_symfs()
> caller passes a path from the profiled system.
>
> Fixes: f182573e06ab ("perf tools: Add layout support for --symfs option")
> Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>

Thanks Zhan! Would it be possible to provide a before and after the
patch so we can better appreciate the issue you are fixing?

Thanks,
Ian

> ---
>  tools/perf/util/build-id.c |  2 +-
>  tools/perf/util/disasm.c   |  4 +++-
>  tools/perf/util/dso.c      | 11 ++++++-----
>  3 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
> index eb95ab90f974..0c89fe75a650 100644
> --- a/tools/perf/util/build-id.c
> +++ b/tools/perf/util/build-id.c
> @@ -599,7 +599,7 @@ static char *build_id_cache__find_debug(const char *sbuild_id,
>                 dirname = dirbuf;
>         }
>
> -       len = __symbol__join_symfs(debugfile, PATH_MAX, dirname);
> +       len = path__join(debugfile, PATH_MAX, symbol_conf.symfs, dirname);
>         snprintf(debugfile + len, PATH_MAX - len, "%.2s/%s.debug", sbuild_id,
>                  sbuild_id + 2);
>
> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> index 0a1a7e9cf3ef..decf9348d735 100644
> --- a/tools/perf/util/disasm.c
> +++ b/tools/perf/util/disasm.c
> @@ -31,6 +31,7 @@
>  #include "map.h"
>  #include "maps.h"
>  #include "namespaces.h"
> +#include "path.h"
>  #include "srcline.h"
>  #include "symbol.h"
>  #include "thread.h"
> @@ -1173,7 +1174,8 @@ static int dso__disassemble_filename(struct dso *dso, char *filename, size_t fil
>
>         build_id_filename = dso__build_id_filename(dso, NULL, 0, false);
>         if (build_id_filename) {
> -               __symbol__join_symfs(filename, filename_size, build_id_filename);
> +               path__join(filename, filename_size, symbol_conf.symfs,
> +                          build_id_filename);
>                 free(build_id_filename);
>         } else {
>                 if (dso__has_build_id(dso))
> diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
> index 2309196d8df3..314c9a0edf28 100644
> --- a/tools/perf/util/dso.c
> +++ b/tools/perf/util/dso.c
> @@ -167,12 +167,12 @@ int dso__read_binary_type_filename(const struct dso *dso,
>                 break;
>
>         case DSO_BINARY_TYPE__FEDORA_DEBUGINFO:
> -               len = __symbol__join_symfs(filename, size, "/usr/lib/debug");
> +               len = path__join(filename, size, symbol_conf.symfs, "/usr/lib/debug");
>                 snprintf(filename + len, size - len, "%s.debug", dso__long_name(dso));
>                 break;
>
>         case DSO_BINARY_TYPE__UBUNTU_DEBUGINFO:
> -               len = __symbol__join_symfs(filename, size, "/usr/lib/debug");
> +               len = path__join(filename, size, symbol_conf.symfs, "/usr/lib/debug");
>                 snprintf(filename + len, size - len, "%s", dso__long_name(dso));
>                 break;
>
> @@ -187,7 +187,7 @@ int dso__read_binary_type_filename(const struct dso *dso,
>                         ret = -1;
>                         break;
>                 }
> -               len = __symbol__join_symfs(filename, size, "/usr/lib/debug");
> +               len = path__join(filename, size, symbol_conf.symfs, "/usr/lib/debug");
>                 snprintf(filename + len, size - len, "%s", dso__long_name(dso) + 4);
>                 break;
>
> @@ -200,7 +200,7 @@ int dso__read_binary_type_filename(const struct dso *dso,
>                 while (last_slash != dso__long_name(dso) && *last_slash != '/')
>                         last_slash--;
>
> -               len = __symbol__join_symfs(filename, size, "");
> +               len = path__join(filename, size, symbol_conf.symfs, "");
>                 dir_size = last_slash - dso__long_name(dso) + 2;
>                 if (dir_size > (size - len)) {
>                         ret = -1;
> @@ -219,7 +219,8 @@ int dso__read_binary_type_filename(const struct dso *dso,
>                 }
>
>                 build_id__snprintf(dso__bid(dso), build_id_hex, sizeof(build_id_hex));
> -               len = __symbol__join_symfs(filename, size, "/usr/lib/debug/.build-id/");
> +               len = path__join(filename, size, symbol_conf.symfs,
> +                                "/usr/lib/debug/.build-id/");
>                 snprintf(filename + len, size - len, "%.2s/%s.debug",
>                          build_id_hex, build_id_hex + 2);
>                 break;
> --
> 2.43.0
>