http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56597
Bug #: 56597
Summary: unaligned local variable used by implicit sse
instructions
Classification: Unclassified
Product: gcc
Version: 4.7.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: kruglin...@gmail.com
I belive that i found an issue in gcc 4.7.2
this afternoon I was compile the google angleproject - a gles2 implementation
on d3d9.
this project require SSE2 support to compiled, so I enable it with
"-march=nocona -O3" to get this work done, finally I got the Dlls.
but when I try to run a test program compiled by VC++ that use the Dlls
compiled by gcc, it always crashed by "Access Violation".
after some analyses, I located the crashed point is a function at
"src\libGLESv2\ProgramBinary.cpp" line 2681 named "bool
ProgramBinary::validateSamplers(InfoLog *infoLog)"
there are some statement in it:
bool ProgramBinary::validateSamplers(InfoLog *infoLog)
{
// if any two active samplers in a program are of different types, but
refer to the same
// texture image unit, and this is the current program, then
ValidateProgram will fail, and
// DrawArrays and DrawElements will issue the INVALID_OPERATION error.
const unsigned int maxCombinedTextureImageUnits =
getContext()->getMaximumCombinedTextureImageUnits();
TextureType textureUnitType[MAX_COMBINED_TEXTURE_IMAGE_UNITS_VTF];
//TextureType is an enum
//MAX_COMBINED_TEXTURE_IMAGE_UNITS_VTF==20
//comment by jjwang
for (unsigned int i = 0; i < MAX_COMBINED_TEXTURE_IMAGE_UNITS_VTF; ++i)
{
textureUnitType[i] = TEXTURE_UNKNOWN;
}
...
}
gcc generate six sse2 "movdqa" instructions to unrolling the loop, great works!
but the textureUnitType is not aligned by 32 bytes, so It crashed!
movdqa xmm0,xmmword ptr ds:[67B4A7D0h]
movdqa xmmword ptr [esp+10h],xmm0;<=====crashed here
movdqa xmmword ptr [esp+20h],xmm0
movdqa xmmword ptr [esp+30h],xmm0
movdqa xmmword ptr [esp+40h],xmm0
movdqa xmmword ptr [esp+50h],xmm0
then I made some changes and it works perfectly!
__attribute__((aligned(32))) TextureType
textureUnitType[MAX_COMBINED_TEXTURE_IMAGE_UNITS_VTF];
the implicit issue like this are very hard to understand for someone never know
sse2 and just want to use the Dlls project. I belive that align the "local
variable" that used by
implicit sse instructions is compiler's work not human's, so think about it
please!
sorry my poor english, thanks!
03-11-2003 jjwang
