[Bug libc/16431] New: PowerPC: gettimeofday calling from glibc internal symbol redirects to system call version

["azanella at linux dot vnet.ibm.com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=16431

            Bug ID: 16431
           Summary: PowerPC: gettimeofday calling from glibc internal
                    symbol redirects to system call version
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: azanella at linux dot vnet.ibm.com
                CC: drepper.fsp at gmail dot com

The PowerPC gettimeofday implementation
(sysdeps/unix/sysv/linux/powerpc/gettimeofday.c) relies on IFUNC selection to
use the vDSO implementation (if it is provided by kernel) or a fallback symbol
that uses a system call.

The IFUNC selector for gettimeofday runs before _libc_vdso_platform_setup where
__vdso_gettimeofday is set. The selector then sets __gettimeofday (the internal
version used within GLIBC) to use the system call version instead of the vDSO
one.

Although this does not lead to wrong behavior, a possible performance leverage
would be to change the way IFUNC resolver get the vDSO to call _dl_vdso_vsym
directly instead of relying in __vdso_gettimeofday value (much like as x86_64
does).

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