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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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