Re: [PATCH v3 09/37] nptl: Move __pthread_unwind_next into libc

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella via Libc-alpha:

> On 16/03/2021 14:29, Florian Weimer via Libc-alpha wrote:
>> It's necessary to stub out __libc_disable_asynccancel and
>> __libc_enable_asynccancel via rtld-stubbed-symbols because the new
>> direct references to the unwinder result in symbol conflicts when the
>> rtld exception handling from libc is linked in during the construction
>> of librtld.map.
>
> From where exactly these come from? The *assynccancel should not be
> generated for rtld-* objects.

I think what happens is this: The libc.so objects that are used as a
starting point have them, so the reducer tries to link in those symbols,
and that fails with symbol conflicts.

>> diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
>> index a011d72fa1..060484cdc8 100644
>> --- a/nptl/pthread_cancel.c
>> +++ b/nptl/pthread_cancel.c
>> @@ -23,6 +23,9 @@
>>  #include <atomic.h>
>>  #include <sysdep.h>
>>  #include <unistd.h>
>> +#include <unwind-link.h>
>> +#include <stdio.h>
>> +#include <gnu/lib-names.h>
>>  
>>  int
>>  __pthread_cancel (pthread_t th)
>> @@ -36,7 +39,12 @@ __pthread_cancel (pthread_t th)
>>  
>>  #ifdef SHARED
>>    /* Trigger an error if libgcc_s cannot be loaded.  */
>> -  __pthread_unwind_link_get ();
>> +  {
>> +    struct unwind_link *unwind_link = __libc_unwind_link_get ();
>> +    if (unwind_link == NULL)
>> +      __libc_fatal (LIBGCC_S_SO
>> +		    " must be installed for pthread_cancel to work\n");
>> +  }
>
> Maybe add a inline function for this since it is used on multiple places?

The error message is slightly different because the function name is
different.  __libc_fatal doesn't do format processing, so it has to be
one literal.  So there isn't that much commonality.

Thanks for the review.

Florian