Re: atomic update of profile counters (issue7000044)

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Nov 20, 2013 at 10:48 AM, Andrew Pinski <pinskia@gmail.com> wrote:
> On Wed, Nov 20, 2013 at 10:44 AM, Rong Xu <xur@google.com> wrote:
>> On Tue, Nov 19, 2013 at 5:11 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>> On Tue, Nov 19, 2013 at 5:02 PM, Rong Xu <xur@google.com> wrote:
>>>> Hi all,
>>>>
>>>> I merged this old patch with current trunk. I also make the following changes
>>>> (1) not using weak references. Now every *profile_atomic() has it's
>>>> own .o so that none of them will be in the final binary if
>>>> -fprofile-generate-atomic is not specified.
>>>> (2) more value profilers have the atomic version.
>>>> (3) not link to libatomic. I used to link the libatomic in the
>>>> presence of -fprofile-generate-atomic, per Andrew's suggestion. It
>>>> used to work. But now if I can add -latomic in the SPEC, it cannot
>>>> find the libatomic.so.1 (unless I specify the PATH). I did not find an
>>>> easy way to statically link libatomic.a. Andrew: Do you have any
>>>> suggestion? Or should we let the user link to libatomic.a if the
>>>> builtins are not expanded?
>>>
>>> It should work for an installed GCC.  For testing you might need
>>> something that is included inside testsuite/lib/atomic-dg.exp which
>>> sets the library path to include libatomic build directory.
>>
>> When I change the SPEC to include libatomic,
>> the compiler can find libatomic. I.e. using
>>>> gcc -O2 -fprofile-generate -fprofile-generate-atomic=3 hello_world.c
>> generates a.out without any problem.
>>
>> But since there are both shared and static libatomic in lib64, it
>> chooses to use the dynamic one.
>>>> ldd a.out
>> linux-vdso.so.1 =>  (0x00007fff56bff000)
>> libatomic.so.1 => not found
>> libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00002b0720261000)
>> /lib64/ld-linux-x86-64.so.2 (0x00002b072003c000)
>>
>>>> ./a.out
>> ./a.out: error while loading shared libraries: libatomic.so.1: cannot
>> open shared object file: No such file or directory
>>
>> while
>>>> LD_LIBRARY_PATH=<gcc_install_patch>/lib64 ./a.out
>> works fine.
>
>
> I don't see this as an issue really as you have the same issue with
> all the target libraries (not limited to libatomic or libgomp or
> libgfortran).

You also also use --as-needed/--no-as-needed wrapped around the
-latomic too;  USE_LD_AS_NEEDED is needed to be used to check for
--as-needed support and LD_AS_NEEDED_OPTION/LD_NO_AS_NEEDED_OPTION
should be used instead of directly --as-needed/--no-as-needed.

>
> Thanks,
> Andrew Pinski
>
>>
>> I think that's the same reason we set the library path in
>> testsuite/lib/atomic-dg.exp, because <gcc_install_patch>/lib64
>> is not in the dynamic library search list.
>>
>> 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.
>>
>> Index: gcc.c
>> ===================================================================
>> --- gcc.c       (revision 205053)
>> +++ gcc.c       (working copy)
>> @@ -771,7 +771,8 @@
>>      %{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\
>> +      %{fprofile-generate-atomic=*:-Wl,-Bstatic -latomic
>> -Wl,-Bdynamic}} " SANITIZER_SPEC " \
>>      %{!nostdlib:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}\
>>      %{!nostdlib:%{!nostartfiles:%E}} %{T*} }}}}}}"
>>  #endif
>>
>>
>>
>>> I think now we require libatomic in more cases (C11 atomic support for
>>> an example).
>>>
>>> Thanks,
>>> Andrew Pinski
>>>
>>>>
>>>> Is this OK for trunk?
>>>>
>>>> Thanks,
>>>>
>>>> -Rong
>>>>
>>>> On Mon, Jan 7, 2013 at 12:55 PM, Rong Xu <xur@google.com> wrote:
>>>>> Function __gcov_indirect_call_profiler_atomic (which contains call to
>>>>> the atomic function) is always emitted in libgcov.
>>>>> Since we only link libatomic when -fprofile-gen-atomic is specified,
>>>>> we have to make the atomic function weak -- otherwise, there is a
>>>>> unsat for regular FDO gen build (of course, when the builtin is not
>>>>> expanded).
>>>>>
>>>>> An alternative it to always link libatomic together with libgcov. Then
>>>>> we don't need the weak stuff. I'm not sure when one is better.
>>>>>
>>>>> -Rong
>>>>>
>>>>> On Mon, Jan 7, 2013 at 12:36 PM, Richard Henderson <rth@redhat.com> wrote:
>>>>>> On 01/03/2013 04:42 PM, Rong Xu wrote:
>>>>>>> It links libatomic when -fprofile-gen-atomic is specified for FDO
>>>>>>> instrumentation build. Here I assume libatomic is always installed.
>>>>>>> Andrew: do you think if this is reasonable?
>>>>>>>
>>>>>>> It also disables the functionality if target does not support weak
>>>>>>> (ie. TARGET_SUPPORTS_WEAK == 0).
>>>>>>
>>>>>> Since you're linking libatomic, you don't need weak references.
>>>>>>
>>>>>> I think its ok to assume libatomic is installed, given that the
>>>>>> user has had to explicitly use the command-line option.
>>>>>>
>>>>>>
>>>>>> r~