[Bug c++/48659] New: Segmentation fault when using openMP and SSE
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48659 Summary: Segmentation fault when using openMP and SSE Product: gcc Version: 4.5.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ AssignedTo: unassig...@gcc.gnu.org ReportedBy: npo...@quick.cz Created attachment 24026 --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24026 A code snippet that reproduces the error g++ tries to save an xmm register using MOVAPD (SSE instruction) to the stack when switching between working chunks during openMP multithreading. This obviously causes a random segmentation fault when the stack pointer happens not be aligned to a 16-byte boundary. Please see the attached code. I compile it with g++ 4.5.2 (I'm using MinGW) and flags -O3 -msse3 -fopenmp. It is important that the optimization is on and the compiler tries to save the xmm register containing the constant zero between working chunks. This is the instruction that causes the segmentation fault if ebp-0x48 is not divisible by 0x10: 0040143a: movapd %xmm1,-0x48(%ebp) // right here 0040143f: call 0x4014bc PS. I have to admit that I'm completely new to GCC, openMP or SSE (I just learned about openMP today and I've playing with them for a couple hours only), so I might be just doing something really stupid.
[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001 Norbert Pozar changed: What|Removed |Added Severity|major |critical
[Bug target/49001] New: GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001
Summary: GCC uses VMOVAPS/PD AVX instructions to access stack
variables that are not 32-byte aligned
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: target
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: npo...@quick.cz
I'm using a custom mingw64 build of GCC 4.6.1. My target is Windows 64bit. I
compile with g++ -03 -march=corei7-avx -mtune=corei7-avx -mavx.
GCC uses aligned moves VMOVAPS/PD from the new AVX instruction set to access
local variables of type __m256/__m256d on the stack. But the stack pointer is
only 16byte aligned on Win64, so this causes a segmentation fault error when
the stack pointer is not 32byte aligned, as in:
__m256 dummy_ps256;
void test_stackalign32() {
__m256 x = dummy_ps256;
dummy_ps256 = sin256_ps_avx(x);
}
which compiles to
vmovapsdummy_ps256(%rip), %ymm0
leaq32(%rsp), %rdx
vmovaps%ymm0, 32(%rsp) // possible SEGFAULT
leaq64(%rsp), %rcx
vzeroupper
call_Z13sin256_ps_avxDv8_f
vmovaps64(%rsp), %ymm0 // possible SEGFAULT
I couldn't figure out how to realign a stack with -mstackrealign.
[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001 --- Comment #3 from Norbert Pozar 2011-05-16 06:05:37 UTC --- (In reply to comment #1) > Please provide testcase that can be compiled without changes. See [1]. I'm sorry about this. > Probably mingw64 specific problem... CC added. Thank you for your time to test the code on linux. I was worried that this might be mingw64 specific. (In reply to comment #2) > Stack alignment isn't supported on Windows. Since this bug effectively prevents using 256bit AVX instructions when compiling for Windows using GCC, I was wondering if there are any plans to support the stack alignment. It seems that simply adding andq$-32, %rsp to the function prologue would fix this. Or would it be feasible to replace VMOVAPS by unaligned VMOVUPS when accessing the stack?
