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SubjectRe: [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@gmail.com> wrote:
>
> From: elisabeth <paniii94@gmail.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@leaningtech.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-perf-users@vger.kernel.org

Acked-by: Namhyung Kim <namhyung@kernel.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
>

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