linux-kernel - Re: [PATCH v2] Subject: perf jit: Fix incorrect file name in DWARF line table

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Date:   Fri, 2 Jun 2023 18:37:58 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Elisabeth <paniii94@...il.com>
Cc:     Elisabeth Panholzer <elisabeth@...ningtech.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2] Subject: perf jit: Fix incorrect file name in DWARF
 line table

Hello,

On Fri, Jun 2, 2023 at 5:38 AM Elisabeth <paniii94@...il.com> wrote:
>
> From: elisabeth <paniii94@...il.com>
>
> Fixes an issue where an incorrect filename was added in the DWARF line table of
> an ELF object file when calling 'perf inject --jit' due to not checking the
> filename of a debug entry against the repeated name marker (/xff/0).
> The marker is mentioned in the tools/perf/util/jitdump.h header, which describes
> the jitdump binary format, and indicitates that the filename in a debug entry
> is the same as the previous enrty.
> In the function emit_lineno_info(), in the file tools/perf/util/genelf-debug.c,
> the debug entry filename gets compared to the previous entry filename. If they
> are not the same, a new filename is added to the DWARF line table. However,
> since there is no check against '\xff\0', in some cases '\xff\0' is inserted
> as the filename into the DWARF line table.
> This can be seen with `objdump --dwarf=line` on the ELF file after `perf inject --jit`.
> It also makes no source code information show up in 'perf annotate'.
>
> Signed-off-by: Elisabeth Panholzer <elisabeth@...ningtech.com>
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-perf-users@...r.kernel.org

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
> Changes in v2:
>         - Made the commit message more descriptive
>         - Added a comment that mentions the jitdump format
>         - Changed memcmp() to strcmp()
>
>  tools/perf/util/genelf_debug.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/genelf_debug.c b/tools/perf/util/genelf_debug.c
> index aa5dcc56b2ac..138fdf87eaa2 100644
> --- a/tools/perf/util/genelf_debug.c
> +++ b/tools/perf/util/genelf_debug.c
> @@ -337,6 +337,9 @@ static void emit_lineno_info(struct buffer_ext *be,
>  {
>         size_t i;
>
> +       /* as described in the jitdump format */
> +       const char repeated_name_marker[] = {'\xff', '\0'};
> +
>         /*
>          * Machine state at start of a statement program
>          * address = 0
> @@ -363,7 +366,8 @@ static void emit_lineno_info(struct buffer_ext *be,
>                 /*
>                  * check if filename changed, if so add it
>                  */
> -               if (!cur_filename || strcmp(cur_filename, ent->name)) {
> +               if ((!cur_filename || strcmp(cur_filename, ent->name)) &&
> +                       strcmp(repeated_name_marker, ent->name)) {
>                         emit_lne_define_filename(be, ent->name);
>                         cur_filename = ent->name;
>                         emit_set_file(be, ++cur_file_idx);
> --
> 2.34.1
>