[git commit master] nptl: mark symbols with libc forwarder hidden

[Carmelo AMOROSO]

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On 9/20/2010 1:20 PM, Timo Teräs wrote:
> On 09/20/2010 01:46 PM, Carmelo AMOROSO wrote:
>  > On 4/23/2010 4:31 PM, Timo Teräs wrote:
>  >> diff --git a/libpthread/nptl/init.c b/libpthread/nptl/init.c
>  >> index b651a3e..87c08fa 100644
>  >> --- a/libpthread/nptl/init.c
>  >> +++ b/libpthread/nptl/init.c
>  >> @@ -111,8 +111,8 @@ static const struct pthread_functions pthread_functions =
>  >> .ptr___pthread_key_create = __pthread_key_create_internal,
>  >> .ptr___pthread_getspecific = __pthread_getspecific_internal,
>  >> .ptr___pthread_setspecific = __pthread_setspecific_internal,
>  >> - .ptr__pthread_cleanup_push_defer = __pthread_cleanup_push_defer,
>  >> - .ptr__pthread_cleanup_pop_restore = __pthread_cleanup_pop_restore,
>  >> + .ptr__pthread_cleanup_push_defer = _pthread_cleanup_push_defer,
>  >> + .ptr__pthread_cleanup_pop_restore = _pthread_cleanup_pop_restore,
>  >> .ptr_nthreads = &__nptl_nthreads,
>  >> .ptr___pthread_unwind = &__pthread_unwind,
>  >> .ptr__nptl_deallocate_tsd = __nptl_deallocate_tsd,
>  >
>  > sorry for coming to this back with a so long delay, but we have recently
>  > updated our uClibc branch against master, and we have found some
>  > problems to boot with Upstart due to this change.
>  >
>  > I've seen that a following commit has reverted most of the changes done
>  > by this patch, but the init.c has not been reverted.
>  >
>  > Indeed, it's not so clear to me the reason for the change above; could
>  > you explain better ?
> 
> IRC the change idea is to prohibit any library (preload, or linked
> before pthread/libc) to override the _pthread_cleanup_* functions. I
> believe this is the intended behavior, because if we eventually get to
> libc pthread call we have already traversed through all the hooks and
> should dispatch the call to the actual real implementation in
> libpthread. This is also the way glibc version works.
> 
>  > Anyway I can say that with this change in place, Upstart cannot work
>  > properly: we got a segfault and I guess it's due to a stack overflow.
>  >
>  > Changing it back to the original version, allowed us to boot successfully.
>  >
>  > What is your opinion ?
> 
> The commit was reverted due to some corner cases how libc and libpthread
> use each other's symbols. The revert again made the original test case
> fail. This was later fixed in using protected symbols in commit:
> a501a33e9761f32b3d38ab9f113892abe7cef3f1
> 
> Which hardware you are using? The patch fails to run if ld.so does not
> support protected symbols properly. See commits:
> ba38f0cec27b91cc7c605417ad047c4dc77d732f (x86)
> 48fb264beaac8114e5ac3e80e70dda473fbce96d (arm)
> 
> Preferably implement protected symbol on your architecture. Reverting
> the init.c change will likely make my original test case fail again
> which is one of:
> 1) linking -lc -lpthread (libc before libpthread)
> 2) linking without -lpthread, but later dlopen a library linking
> against -lpthread
> 
> Hopefully this explains it a bit. I do remember that getting all the
> corner cases right was extremely tricky, and I tested it later only on
> x86. But most likely it's the protected symbol thingy that's missing for
> you.
> 
> - Timo
> 

Hi Timo,
thanks for your explanation (I will read the original thread again).
I think you have caught the point... "protected" symbol support (I
forgot it); and my arch (sh4) is missing it.

So it's time to work on it on sh4 too.

Thanks,
Carmelo
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