Broken PIC support in OS X
Manuel M T Chakravarty
chak at cse.unsw.edu.au
Fri Aug 5 07:05:18 CEST 2011
GMP version 5.0.2
OS/arch: OS X 10.7 (Lion), x86_64
Compiler: gcc 4.2 (Xcode 4.1)
When compiling GMP 5.0.2 on the specified system, assembly code (such as 'mpn/x86_64/bdiv_q_1.asm') is incorrectly compiled without support for PIC. According to Apple documentation, the x86_64 code model for Mach-O always requires PIC:
As a result PIC is the default and doesn't need to be specified when compiling or linking. Assembly code that doesn't adhere to this convention leads to a link time warning of the form
ld: warning: PIE disabled. Absolute addressing (perhaps -mdynamic-no-pic) not allowed in code signed PIE
The linker will still produce a binary, but it is not position independent.
To test, simply pre-process an assembly file, e.g.,
m4 -DHAVE_CONFIG_H -D__GMP_WITHIN_GMP -DOPERATION_bdiv_q_1 bdiv_q_1.asm >tmp-bdiv_q_1.s
The resulting assembly code will load a global table address with
movabs $binvert_limb_table, %rdx
instead of with
mov binvert_limb_table at GOTPCREL(%rip), %rdx
I append a patch that fixes the problem.
PS: I tested this on OS X 10.7, but believe the same issues arises on 10.6 for x86_64 and recent versions of Xcode.
-=- Patch to ensure PIC support is used on OS X/x64_64 -=-
--- gmp-5.0.2.orig/configure.in 2011-08-04 16:35:01.000000000 +1000
+++ gmp-5.0.2/configure.in 2011-08-04 16:39:03.000000000 +1000
@@ -3178,6 +3178,7 @@
case $host in
--- gmp-5.0.2.orig/mpn/asm-defs.m4 2011-08-04 23:11:19.000000000 +1000
+++ gmp-5.0.2/mpn/asm-defs.m4 2011-08-04 23:11:59.000000000 +1000
@@ -1041,7 +1041,7 @@
dnl systems which are always PIC. PIC_ALWAYS established in config.m4
dnl identifies these for us.
dnl Various possible defines passed from the Makefile that are to be tested
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