linux-kernel - Re: [PATCH] perf jit: Fix inaccurate DWARF line table

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Message-ID: <CAP-5=fWCLq+2xjViJaYxFs9b=3BxSvKmVAdv6xX3re8AoBLHWg@mail.gmail.com>
Date:   Thu, 28 May 2020 00:44:56 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Nick Gasson <nick.gasson@....com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf jit: Fix inaccurate DWARF line table

On Wed, May 27, 2020 at 10:19 PM Nick Gasson <nick.gasson@....com> wrote:
>
> Fix an issue where addresses in the DWARF line table are offset by
> -0x40 (GEN_ELF_TEXT_OFFSET). This can be seen with `objdump -S` on the
> ELF files after perf inject.

Without too much knowledge this looks good to me. The original code
came from oprofile's jit support:
https://sourceforge.net/p/oprofile/oprofile/ci/master/tree/opjitconv/debug_line.c#l325

Acked-by: Ian Rogers <irogers@...gle.com>

> Signed-off-by: Nick Gasson <nick.gasson@....com>
> ---
>  tools/perf/util/genelf_debug.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/genelf_debug.c b/tools/perf/util/genelf_debug.c
> index 30e9f618f6cd..dd40683bd4c0 100644
> --- a/tools/perf/util/genelf_debug.c
> +++ b/tools/perf/util/genelf_debug.c
> @@ -342,7 +342,7 @@ static void emit_lineno_info(struct buffer_ext *be,
>          */
>
>         /* start state of the state machine we take care of */
> -       unsigned long last_vma = code_addr;
> +       unsigned long last_vma = 0;
>         char const  *cur_filename = NULL;
>         unsigned long cur_file_idx = 0;
>         int last_line = 1;
> @@ -473,7 +473,7 @@ jit_process_debug_info(uint64_t code_addr,
>                 ent = debug_entry_next(ent);
>         }
>         add_compilation_unit(di, buffer_ext_size(dl));
> -       add_debug_line(dl, debug, nr_debug_entries, 0);
> +       add_debug_line(dl, debug, nr_debug_entries, GEN_ELF_TEXT_OFFSET);
>         add_debug_abbrev(da);
>         if (0) buffer_ext_dump(da, "abbrev");
>
> --
> 2.26.2
>