Re: atomic update of profile counters (issue7000044)

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Nov 20, 2013 at 2:07 PM, Rong Xu <xur@google.com> wrote:
> 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.


I think Joseph's suggestion was also to include -latomic even when not
generating atomic profiling due to the C11 code requiring it.

Thanks,
Andrew

>
> 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
> <joseph@codesourcery.com> 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
>> joseph@codesourcery.com