https://bugs.freedesktop.org/show_bug.cgi?id=33440
Summary: _gl_DispatchTSD in glapi_x86_64.S has incorrect
relocation type
Product: Mesa
Version: git
Platform: x86-64 (AMD64)
OS/Version: All
Status: NEW
Severity: normal
Priority: medium
Component: Mesa core
AssignedTo: mesa-dev@lists.freedesktop.org
ReportedBy: dimi...@andric.com
Created an attachment (id=42416)
--> (https://bugs.freedesktop.org/attachment.cgi?id=42416)
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.
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