[uClinux-dev] Transactional Memory (TM) in GCC 4.7 breaks uClinux -msep-data (-fPIC)

Larry Baker baker at usgs.gov
Tue Sep 25 14:05:19 EDT 2012

See my posting at http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54584, Bug 54584 - m68k-uclinux error: Link tests are not allowed after GCC_NO_EXECUTABLES.

The problem is a program always includes a size 0 section, .tm_clone_table, from crtbegin.o/crtend.o (libgcc/crtstuff.c), even though the program does not use the -gnu-tm option.  I'm guessing the .tm_clone_table __attribute__ ((used)) results in the ALLOC flag for the section, which causes the linker (ld? elf2flt?) to croak when there is nothing to allocate.  Linking without -elf2flt does not fail, and results in an image without a .tm_clone_table section.  I don't know why the linker for -msep-data/-fPIC code can't figure out how to do the same thing.

My workaround is to disable USE_TM_CLONE_REGISTRY in gcc/config/m68k/uclinux.h (this patch is good for both GCC 4.7 and GCC 4.8):

--- gcc-4.7-20120908/gcc/config/m68k/uclinux.h
+++ gcc-4.7-20120908-patched/gcc/config/m68k/uclinux.h
@@ -22,2 +22,4 @@

+/* Do not use TM clone registry.  It breaks -msep-data (-fPIC) code. */

Larry Baker
US Geological Survey
baker at usgs.gov

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