[FFmpeg-trac] #6516(build system:new): tsan symbols broken are broken with NASM

[FFmpeg]

#6516: tsan symbols broken are broken with NASM
-------------------------------------+-------------------------------------
               Reporter:  ubitux     |                  Owner:
                   Type:  defect     |                 Status:  new
               Priority:  normal     |              Component:  build
                Version:             |  system
  unspecified                        |               Keywords:  regression
             Blocked By:             |  tsan
Reproduced by developer:  1          |               Blocking:
                                     |  Analyzed by developer:  0
-------------------------------------+-------------------------------------
 Since the switch from YASM to NASM, thread sanitizer is unusable by
 default:

 {{{
 WARNING: ThreadSanitizer: data race (pid=21662)
   Read of size 8 at 0x7b9800003008 by main thread (mutexes: write M1355):
     #0 <null> <null> (libtsan.so.0+0x000000030111)
     #1 <null> <null> (ffmpeg+0x000000d5481f)
     #2 <null> <null> (ffmpeg+0x000000d054e1)
     #3 <null> <null> (ffmpeg+0x000000e134d7)
     #4 <null> <null> (ffmpeg+0x000000e13ba8)
     #5 <null> <null> (ffmpeg+0x000000a1553f)
     #6 <null> <null> (ffmpeg+0x000000a1609a)
     #7 <null> <null> (ffmpeg+0x00000050e4e4)
     #8 <null> <null> (ffmpeg+0x000000510bb5)
     #9 <null> <null> (ffmpeg+0x0000004d6d3b)
     #10 <null> <null> (libc.so.6+0x000000020439)
 }}}

 This may be related to the way NASM stores dwarf symbols.

 Note: tested only with gcc-tsan.

 Note: we probably need to open a ticket on the NASM bugtracker if it's
 concluded we didn't mixed up incompatible options in our build system.
 Still, I consider this a regression since NASM wasn't the default
 previously.

 Workaround: use {{{--x86asmexe=yasm}}}.

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Ticket URL: <https://trac.ffmpeg.org/ticket/6516>
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