| Summary: | _gl_DispatchTSD in glapi_x86_64.S has incorrect relocation type | ||
|---|---|---|---|
| Product: | Mesa | Reporter: | Dimitry Andric <dimitry> |
| Component: | Mesa core | Assignee: | mesa-dev |
| Status: | RESOLVED FIXED | QA Contact: | |
| Severity: | normal | ||
| Priority: | medium | ||
| Version: | git | ||
| Hardware: | x86-64 (AMD64) | ||
| OS: | All | ||
| Whiteboard: | |||
| i915 platform: | i915 features: | ||
| Attachments: |
Change relocation type of _gl_DispatchTSD to GOTPCREL
Change relocation type of _gl_DispatchTSD to GOTPCREL, take 2 |
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Thanks. Committed as 731ec60da3ccb92f5bfb4d6f1bc3c8e712751376 This patch causes a segfault in all 3D apps on Linux (64-bit on AMD Phenom 9350e). I've reverted the patch. Dimitry, can you look into this again? Created attachment 42610 [details] [review] Change relocation type of _gl_DispatchTSD to GOTPCREL, take 2 Okay, I think I have now determined the proper way to solve this issue. I should have examined my own gcc example more closely... :) When Mesa is using pthreads, _gl_DispatchTSD is actually an instance of the following struct: struct u_tsd { pthread_key_t key; int initMagic; }; The purpose of _x86_64_get_dispatch is to get the pthread-specific data associated with the key (normally a struct mapi_table pointer). In C this would be: void *_x86_64_get_dispatch(void) { return pthread_getspecific(_gl_DispatchTSD.key); } which, using -fPIC, gets compiled by gcc to: _x86_64_get_dispatch: movq _gl_DispatchTSD@GOTPCREL(%rip), %rax movl (%rax), %edi jmp pthread_getspecific@PLT E.g. the _gl_DispatchTSD@GOTPCREL(%rip) reference gives a pointer to the start of the struct, which gets stored in %rax. Then, the pointer is dereferenced to get the first member of the struct: an unsigned int on Linux, even on x86-64 (on FreeBSD, it's a regular int). It is stored in %edi, to serve as first parameter to pthread_getspecific(), which is tail-called. So please try this revised patch, which I have actually tested to run properly on Linux. Seem to work fine here on 64-bit Linux. Works for me too. Committed (cfb9aae3ec4e42bd9be8445039dc52b8d6c71f9c). |
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Created attachment 42416 [details] Change relocation type of _gl_DispatchTSD to GOTPCREL While building Mesa on FreeBSD, with recent binutils (>2.17), libGL.so.1 will fail to link with a misleading error: ... mklib: Making FreeBSD shared library: libGL.so.1 /usr/bin/ld: ../../../src/mesa/x86-64/glapi_x86-64.o: relocation R_X86_64_PC32 against `_gl_DispatchTSD' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: Bad value But of course, the glapi_x86-64.o file is already compiled with -fPIC, the actual command line used is: cc -c -I. -I../../../include -I../../../include/GL/internal -I../../../src/mesa -I../../../src/mesa/glapi -I/usr/local/include -I/usr/local/include/drm -I/usr/local/include -D_THREAD_SAFE -I/usr/local/include -I/usr/local/include -O2 -pipe -fno-strict-aliasing -Wall -Wmissing-prototypes -std=c99 -ffast-math -fno-strict-aliasing -fPIC -DUSE_X86_64_ASM -DHAVE_POSIX_MEMALIGN -DUSE_XCB -DPTHREADS -DUSE_EXTERNAL_DXTN_LIB=1 -DIN_DRI_DRIVER -DHAVE_ALIAS -DGLX_INDIRECT_RENDERING -DGLX_DIRECT_RENDERING -DXF86VIDMODE -D_REENTRANT -UIN_DRI_DRIVER -DDEFAULT_DRIVER_DIR=\"/usr/local/lib/dri\" ../../../src/mesa/x86-64/glapi_x86-64.S -o ../../../src/mesa/x86-64/glapi_x86-64.o The problem in glapi_x86-64.S is that if PTHREADS is defined, _gl_DispatchTSD is declared as .extern, but is then accessed directly with _gl_DispatchTSD(%rip), which is only applicable to locally defined objects: #elif defined(PTHREADS) .extern _glapi_Dispatch .extern _gl_DispatchTSD # If this is extern... .extern pthread_getspecific .p2align 4,,15 _x86_64_get_dispatch: movq _gl_DispatchTSD(%rip), %rdi # ...this is incorrect jmp pthread_getspecific@PLT Instead, this access to _gl_DispatchTSD needs to be qualified with @GOTPCREL, to indicate the symbol is relative to the Global Offset Table, e.g.: movq _gl_DispatchTSD@GOTPCREL(%rip), %rdi (This was also found out by José Fonseca in one of his side branches, commit b09d1ef60dae3b3c44f1370fd2f726c7044bc17) As an example, consider the following small piece of C code: extern int foo; int bar(void) { return foo + 42; } If you compile this on x86-64 with "gcc -O2 -fPIC -S", so for use in a shared library, it will result in (approximately); .globl bar .type bar, @function bar: .LFB2: movq foo@GOTPCREL(%rip), %rax movl (%rax), %eax addl $42, %eax ret Again, since the glapi_x86-64.S file is generated from gl_x86-64_asm.py, I changed both.