Joseph and Andrew, thanks for the suggestion. That's really helpful.
Here is the new patch for gcc.c.
Basically, it's just what you have suggested: enclosing -latomic with
--as-needed, and using macros.
For the case of no --as-needed support, I use static link. (just found
that some code already using this in the SPEC).
I'm flexible on this part -- if you think this is unnecessary, I can remove.
Thanks,
-Rong
Index: gcc.c
===================================================================
--- gcc.c (revision 205053)
+++ gcc.c (working copy)
@@ -748,6 +748,23 @@ proper position among the other output files. */
%{fvtable-verify=preinit: -lvtv -u_vtable_map_vars_start
-u_vtable_map_vars_end}}"
#endif
+/* This spec is for linking in libatomic in gcov atomic counter update.
+ We will use the atomic functions defined in libatomic, only when the builtin
+ versions are not available. In the case of no LD_AS_NEEDED support, we
+ link libatomic statically. */
+
+#ifndef GCOV_ATOMIC_SPEC
+#if USE_LD_AS_NEEDED
+#define GCOV_ATOMIC_SPEC "%{fprofile-generate-atomic=*:" LD_AS_NEEDED_OPTION \
+ " -latomic} " LD_NO_AS_NEEDED_OPTION
+#elif defined(HAVE_LD_STATIC_DYNAMIC)
+#define GCOV_ATOMIC_SPEC "%{fprofile-generate-atomic=*:" LD_STATIC_OPTION \
+ " -latomic " LD_DYNAMIC_OPTION "}"
+#else /* !USE_LD_AS_NEEDED && !HAVE_LD_STATIC_DYNAMIC */
+#define GCOV_ATOMIC_SPEC "%{fprofile-generate-atomic=*:-latomic}"
+#endif
+#endif
+
/* -u* was put back because both BSD and SysV seem to support it. */
/* %{static:} simply prevents an error message if the target machine
doesn't handle -static. */
@@ -771,7 +788,8 @@ proper position among the other output files. */
%{fopenmp|ftree-parallelize-loops=*:%:include(libgomp.spec)%(link_gomp)}\
%{fgnu-tm:%:include(libitm.spec)%(link_itm)}\
%(mflib) " STACK_SPLIT_SPEC "\
- %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} " SANITIZER_SPEC " \
+ %{fprofile-arcs|fprofile-generate*|coverage:-lgcov\
+ " GCOV_ATOMIC_SPEC "} " SANITIZER_SPEC " \
%{!nostdlib:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}\
%{!nostdlib:%{!nostartfiles:%E}} %{T*} }}}}}}"
On Wed, Nov 20, 2013 at 1:04 PM, Joseph S. Myers
<[email protected]> wrote:
> On Wed, 20 Nov 2013, Rong Xu wrote:
>
>> I could do this in the SPEC
>> -Wl,-Bstatic -latomic -Wl,-Bdynamic
>> which would link libatomic statically.
>> I works for me. But it looks a little weird in gcc driver.
>
> I think we should generally link libatomic with --as-needed by default on
> platforms supporting --as-needed, in line with the general principle that
> C code just using language not library facilities (_Atomic in this case)
> shouldn't need any special options to link it (libatomic is like libgcc,
> which is linked in automatically); the trickier question is what to do
> with it on any systems supporting shared libraries but not --as-needed.
>
> --
> Joseph S. Myers
> [email protected]
