Re: [glibc] nptl: Add missing placeholder abi symbol from nanosleep move

[Florian Weimer <fweimer at redhat dot com>]

* Adhemerval Zanella:

> On 07/11/2019 13:54, Florian Weimer wrote:
>> * Adhemerval Zanella:
>> 
>>> https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4f4bb489e0ddd2f24b2a5d352bb39f8dcdb38050
>>>
>>> commit 4f4bb489e0ddd2f24b2a5d352bb39f8dcdb38050
>>> Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>>> Date:   Thu Nov 7 15:10:35 2019 +0000
>>>
>>>     nptl: Add missing placeholder abi symbol from nanosleep move
>>>     
>>>     Adds the __libpthread_version_placeholder symbol with the same version
>>>     of nanosleep/__nanosleep that was removed by 79a547b162657b3f and that
>>>     is not provided by other symbols.
>> 
>>> +GLIBC_2.2 __libpthread_version_placeholder F
>> 
>> Sorry, this fix does not look correct to me.  Since GLIBC_2.2 has
>> members (and we can easily detect that), it should not get an additional
>> placeholder symbol.
>> 
>> I think you need to add a symbol alias and another compat_symbol to
>> nptl/libpthread-compat.c.
>
> It is not strictly incorrect, although superfluous.  Ideally we would need
> to add __libpthread_version_placeholder iff there is no other symbol with
> same version already present, however I don't see straightforward to optimize
> the symbol creation without adding some compat symbol hacking.

This change does not look correct:

-#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
+#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2_6))

You need

#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2) \
     || SHLIB_COMPAT (libpthread, GLIBC_2_1_6, GLIBC_2_3))

and then do something like this:

#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
strong_alias (__libpthread_version_placeholder,
              __libpthread_version_placeholder_212)
compat_symbol (libpthread, __libpthread_version_placeholder_212,
               __libpthread_version_placeholder, GLIBC_2_1_2);
#endif
#if (SHLIB_COMPAT (libpthread, GLIBC_2_1_6, GLIBC_2_3))
strong_alias (__libpthread_version_placeholder,
              __libpthread_version_placeholder_226)
compat_symbol (libpthread, __libpthread_version_placeholder_226,
               __libpthread_version_placeholder, GLIBC_2_2_6);
#endif

The strong_alias is needed because some binutils version/target
combinations do not support multiple versions for one symbol.

Thanks,
Florian