This patch uses an ifunc to implement gettimeofday in the shared libc.
This is faster compared to the vsyscall mechanism that has to check a
global pointer, demangle it and call it indirectly when the VDSO is
present. Resolving the gettimeofday symbol directly to the VDSO code
is safe because there are no failures that the libc has to handle by
setting errno like in a generic vsyscall (the only failure when the
VDSO code falls back to a syscall is EFAULT, but passing an invalid
pointer is undefined behaviour so returning -EFAULT is fine).
If the kernel supports the VDSO interface we use it for extern calls,
otherwise the old vsyscall method is used which falls back to a syscall.
The static version of gettimeofday continues to use a syscall, libc.so
internal calls use the old vsyscall method.
* sysdeps/unix/sysv/linux/aarch64/gettimeofday.c: New file.
This patch removes the architecture specific gettimeofday implementation
to use the vDSO symbol and consolidate it on a common Linux one.
Similar to clock_gettime and clock_getres vDSO implementation, each port
that supports gettimeofday through vDSO should just implement INLINE_VSYSCALL
to access the symbol and define HAVE_{GETTIME,GETRES}_VSYSCAL as 1.
This patch consolidate the Linux vDSO define and usage across all ports
that uses it. The common vDSO definitions and calling through
{INLINE/INTERNAL}_VSYSCALL macros are moved to a common header
sysdep-vdso.h and vDSO name declaration and prototype is defined
using a common macro.
Also PTR_{MANGLE,DEMANGLE} is added to ports that does not use them
for vDSO calls (aarch64, powerpc, s390, and tile) and thus it will
reflect in code changes. For ports that already implement pointer
mangling/demangling in vDSO system (i386, x32, x86_64) this patch
is mainly a code refactor.
Checked on x32, x86_64, x32, ppc64le, and aarch64.
This patch moves the AArch64 port to the main sysdeps hierarchy. The
move is essentially:
git mv ports/sysdeps/aarch64 sysdeps/aarch64
git mv ports/sysdeps/unix/sysv/linux/aarch64 sysdeps/unix/sysv/linux/aarch64
The README is updated and I've updated ChangeLog.aarch64 along the
lines of the ARM move. The AArch64 build has been tested to confirm
that there were no changes in objdump -dr output or the shared
objects.
Steve Ellcey
Adhemerval Zanella
Joseph Myers
Marcus Shawcroft