From: Ian Lance Taylor <iant@golang.org>
To: Milian Wolff <milian.wolff@kdab.com>
Cc: GCC <gcc@gcc.gnu.org>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: bugs in external debug info support in libbacktrace
Date: Thu, 25 Jan 2018 18:15:00 -0000 [thread overview]
Message-ID: <CAOyqgcVtGoiFya=CA1y1CQ-wFT7Rh4MoGP9fv=EdGkwUUiKYHA@mail.gmail.com> (raw)
In-Reply-To: <5149137.Ncrl3keaZR@milian-kdab2>
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On Mon, Nov 27, 2017 at 2:23 AM, Milian Wolff <milian.wolff@kdab.com> wrote:
>
> I was made aware that libbacktrace got support for external debug info with
> [1], great work! I have just synced the latest libbacktrace into heaptrack [2]
> in a local branch and played around with it and noticed two limitations:
>
> [1]: https://github.com/gcc-mirror/gcc/commit/
> b919941efc58035debbcf69b645c072b7dd6ba4e
> [2]: https://github.com/KDE/heaptrack
>
> a) elf_open_debugfile_by_debuglink checks the crc, even if it is not provided
> by the debug file. I.e. I have a file where `debuglink_crc == 0`, but the
> got_crc calculated from elf_crc32_file is non-zero. I have patched this
> locally with the following to make it work for me:
>
> diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c
> index 06823fcf59b..24bf58728fd 100644
> --- a/libbacktrace/elf.c
> +++ b/libbacktrace/elf.c
> @@ -1005,7 +1005,7 @@ elf_open_debugfile_by_debuglink (struct backtrace_state
> *state,
> if (ddescriptor < 0)
> return -1;
>
> - got_crc = elf_crc32_file (state, ddescriptor, error_callback, data);
> + got_crc = debuglink_crc ? elf_crc32_file (state, ddescriptor,
> error_callback, data) : 0;
> if (got_crc != debuglink_crc)
> {
> backtrace_close (ddescriptor, error_callback, data);
Thanks. I fixed this problem with a slightly different patch,
appended. Committed to mainline.
> b) elf_add guards the code to inspect the symtab-shndx with a `&& !debuginfo`
> check in loc 2797. This results in all files with separate debug info yielding
> `found_sym = 0` when calling elf_add, and symbol resolution is broken.
> Personally I have patched this check out to make symbol resolution work for
> me:
>
> diff --git a/libbacktrace/elf.c b/libbacktrace/elf.c
> index 06823fcf59b..6876bd3ed8e 100644
> --- a/libbacktrace/elf.c
> +++ b/libbacktrace/elf.c
> @@ -2794,7 +2794,7 @@ elf_add (struct backtrace_state *state, const char
> *filename, int descriptor,
>
> if (symtab_shndx == 0)
> symtab_shndx = dynsym_shndx;
> - if (symtab_shndx != 0 && !debuginfo)
> + if (symtab_shndx != 0)
> {
> const b_elf_shdr *symtab_shdr;
> unsigned int strtab_shndx;
>
> Could you please check whether the two patches above could be upstreamed?
I don't think that's the right approach. In the appended patch I skip
clearing *found_sym if debuginfo is set. I hope that will fix the
problem.
Ian
2018-01-25 Ian Lance Taylor <iant@golang.org>
* elf.c (elf_open_debugfile_by_debuglink): Don't check CRC if the
desired CRC is zero.
(elf_add): Don't clear *found_sym and *found_dwarf if debuginfo.
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Index: elf.c
===================================================================
--- elf.c (revision 257038)
+++ elf.c (working copy)
@@ -997,7 +997,6 @@ elf_open_debugfile_by_debuglink (struct
void *data)
{
int ddescriptor;
- uint32_t got_crc;
ddescriptor = elf_find_debugfile_by_debuglink (state, filename,
debuglink_name,
@@ -1005,11 +1004,16 @@ elf_open_debugfile_by_debuglink (struct
if (ddescriptor < 0)
return -1;
- got_crc = elf_crc32_file (state, ddescriptor, error_callback, data);
- if (got_crc != debuglink_crc)
+ if (debuglink_crc != 0)
{
- backtrace_close (ddescriptor, error_callback, data);
- return -1;
+ uint32_t got_crc;
+
+ got_crc = elf_crc32_file (state, ddescriptor, error_callback, data);
+ if (got_crc != debuglink_crc)
+ {
+ backtrace_close (ddescriptor, error_callback, data);
+ return -1;
+ }
}
return ddescriptor;
@@ -2634,8 +2638,11 @@ elf_add (struct backtrace_state *state,
unsigned int using_debug_view;
uint16_t *zdebug_table;
- *found_sym = 0;
- *found_dwarf = 0;
+ if (!debuginfo)
+ {
+ *found_sym = 0;
+ *found_dwarf = 0;
+ }
shdrs_view_valid = 0;
names_view_valid = 0;
prev parent reply other threads:[~2018-01-25 18:15 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-27 10:23 Milian Wolff
2018-01-25 18:15 ` Ian Lance Taylor [this message]
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