Hi,
I've come across some bug (which I thought might be related to the
gallium-noblocks branch, but it's not) which caused a segfault but only
when not using debug builds. I think this is the same issue Vinson was
seeing some time ago. Looks like a impossible backtrace:
#0 st_texture_image_copy (pipe=0x612640, dst=0x0,
dstLevel=<value optimized out>, src=0x6e1dd0, face=0)
at src/mesa/state_tracker/st_texture.c:306
#1 0x00007ffff759b383 in copy_image_data_to_texture (
ctx=<value optimized out>, pipe=<value optimized out>, tObj=0x6919d0,
needFlush=<value optimized out>)
at src/mesa/state_tracker/st_cb_texture.c:1673
#2 st_finalize_texture (ctx=<value optimized out>,
pipe=<value optimized out>, tObj=0x6919d0, needFlush=<value
optimized out>)
at src/mesa/state_tracker/st_cb_texture.c:1807
#3 0x00007ffff758fd9d in finalize_textures (st=0x68a9c0)
at src/mesa/state_tracker/st_atom_texture.c:144
Segfault seems to be because dst is 0x0, but if you look at the call
stack it is easy to see this is impossible.
That would point to gcc optimizer issue (using gcc 4.4.1), except there
are quite a few warnings during compile, especially about violating
strict-aliasing rules...
So, in the gallium.py scons file there's actually this:
if debug:
ccflags += ['-O0', '-g3']
elif env['CCVERSION'].startswith('4.2.'):
# gcc 4.2.x optimizer is broken
print "warning: gcc 4.2.x optimizer is broken -- disabling
optimizations"
ccflags += ['-O0', '-g3']
else:
ccflags += ['-O3', '-g3']
So I added -fno-strict-aliasing and indeed, segfault is gone. Hence I
believe this is incorrectly accusing the gcc 4.2 optimizer, whereas it's
actually a code bug, and certainly it is not restricted to gcc 4.2
(unless this addressed a different problem).
Not quite sure though why the code violates strict-aliasing rules though
in all places - about half of the warnings are from pipe_reference,
(p_refcount.h:85). Not sure if all warnings are actually real issues,
and not sure how this should be fixed (should we try to fix this for
real or just force -fno-strict-aliasing).
Roland
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