Re: [PATCH] Use libbacktrace as libsanitizer's symbolizer

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Nov 22, 2013 at 10:40:00PM +0400, Konstantin Serebryany wrote:
> [I beg my pardon if this has already been discussed here]
> Does libbacktrace call any functions we intercept (malloc, memset,
> memcpy, strlen, etc)?
> If so, they will have to be un-intercepted there.

Why?

> Our hermetic llvm-symbolizer took as so much work for a reason. :(
> And doing this work for libbacktrace w/o any additional functionality
> for us is kind of sad...

The symbols from libc/libgcc used in my libbacktrace.a are following:

dwarf.o:
                 U bsearch
                 U memcpy
                 U memset
                 U qsort
                 U snprintf
                 U strcmp
                 U strlen
                 U strnlen
posix.o:
                 U close
                 U __errno_location
                 U fcntl
                 U open
print.o:
                 U fprintf
                 U fputc
                 U stderr
                 U strerror
backtrace.o:
                 U _Unwind_Backtrace
                 U _Unwind_GetIPInfo
simple.o:
                 U _Unwind_Backtrace
                 U _Unwind_GetIPInfo
elf.o:
                 U bsearch
                 U dl_iterate_phdr
                 U qsort
                 U strcmp
mmapio.o:
                 U __errno_location
                 U getpagesize
                 U mmap
                 U munmap
mmap.o:
                 U __errno_location
                 U getpagesize
                 U memcpy
                 U mmap

Note that I think neither print.o nor backtrace.o nor simple.o
were actually linked into libasan* with my earlier patch, so 
the list of external symbols is likely just:
                 U bsearch
                 U memcpy
                 U memset
                 U qsort
                 U snprintf
                 U strcmp
                 U strlen
                 U strnlen
                 U close
                 U __errno_location
                 U fcntl
                 U open
                 U dl_iterate_phdr
                 U getpagesize
                 U mmap
                 U munmap

Now, what's wrong in using these symbols while symbolizing something?
All the testing worked just fine for me, are you afraid there will be
bugs in libbacktrace which would trigger recursive diagnostics?

Worst case we could build a special copy of libbacktrace.la inside of
libsanitizer rather than just use the target copy of it built for libgo
(libbacktrace right now is used for GCC itself as host library and
for libgo as target library), just by e.g. adding special
libsanitizer/libbacktrace/Makefile.am rules to look for sources into
../../libbacktrace/ and say wrap libbacktrace's internal.h header so
that it #include_next <internal.h> and then redefines the above mentioned
functions or subset of them to the internal stuff.

But before doing that, the question is why.

	Jakub