From: Milian Wolff <milian.wolff@kdab.com>
To: Ian Lance Taylor <iant@golang.org>
Cc: GCC <gcc@gcc.gnu.org>
Subject: bugs in external debug info support in libbacktrace
Date: Mon, 27 Nov 2017 10:23:00 -0000 [thread overview]
Message-ID: <5149137.Ncrl3keaZR@milian-kdab2> (raw)
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Hey Ian, others,
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);
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?
Thanks a lot for your work
--
Milian Wolff | milian.wolff@kdab.com | Senior Software Engineer
KDAB (Deutschland) GmbH&Co KG, a KDAB Group company
Tel: +49-30-521325470
KDAB - The Qt Experts
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next reply other threads:[~2017-11-27 10:23 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-27 10:23 Milian Wolff [this message]
2018-01-25 18:15 ` Ian Lance Taylor
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