VDSO support for MIPS

This patch adds support for using the implementations of gettimeofday()
and clock_gettime() provided by the kernel in the VDSO. The VDSO will
always provide clock_gettime() as CLOCK_{REALTIME,MONOTONIC}_COARSE can
be implemented regardless of platform. CLOCK_{REALTIME,MONOTONIC}, along
with gettimeofday(), are only implemented on platforms which make use of
either the CP0 count or GIC as their clocksource. On other platforms,
the VDSO does not provide the __vdso_gettimeofday symbol, as it is
never useful.

The VDSO functions return ENOSYS when they encounter an unsupported
request, in which case glibc should fall back to the standard syscall.

Tested with upstream kernel 4.5 and QEMU emulating Malta.

./vdsotest gettimeofday bench
gettimeofday: syscall: 1021 nsec/call
gettimeofday:    libc: 262 nsec/call
gettimeofday:    vdso: 174 nsec/call

	* sysdeps/unix/sysv/linux/mips/Makefile (sysdep_routines):
	Include dl-vdso.
	* sysdeps/unix/sysv/linux/mips/Versions: Add
	__vdso_clock_gettime.
	* sysdeps/unix/sysv/linux/mips/init-first.c: New file.
	* sysdeps/unix/sysv/linux/mips/libc-vdso.h: New file.
	* sysdeps/unix/sysv/linux/mips/mips32/sysdep.h:
	(INTERNAL_VSYSCALL_CALL): Define to be compatible with MIPS
	definitions of INTERNAL_SYSCALL_{ERROR_P,ERRNO}.
	(HAVE_CLOCK_GETTIME_VSYSCALL): Define.
	(HAVE_GETTIMEOFDAY_VSYSCALL): Define.
	* sysdeps/unix/sysv/linux/mips/mips64/n32/sysdep.h: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/n64/sysdep.h: Likewise.

1 files changed, 16 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/mips/mips32/sysdep.h b/sysdeps/unix/sysv/linux/mips/mips32/sysdep.h
index 2160df7d59..2335409628 100644
--- a/sysdeps/unix/sysv/linux/mips/mips32/sysdep.h
+++ b/sysdeps/unix/sysv/linux/mips/mips32/sysdep.h
@@ -371,6 +371,22 @@
 #define __SYSCALL_CLOBBERS "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13", \
 	"$14", "$15", "$24", "$25", "hi", "lo", "memory"
 
+/* Standard MIPS syscalls have an error flag, and return a positive errno
+   when the error flag is set. Emulate this behaviour for vsyscalls so that
+   the INTERNAL_SYSCALL_{ERROR_P,ERRNO} macros work correctly.  */
+#define INTERNAL_VSYSCALL_CALL(funcptr, err, nr, args...)		\
+  ({									\
+    long _ret = funcptr (args);						\
+    err = ((unsigned long) (_ret) >= (unsigned long) -4095L);		\
+    if (err)								\
+      _ret = -_ret;							\
+    _ret;								\
+  })
+
+/* List of system calls which are supported as vsyscalls.  */
+#define HAVE_CLOCK_GETTIME_VSYSCALL	1
+#define HAVE_GETTIMEOFDAY_VSYSCALL	1
+
 #endif /* __ASSEMBLER__ */
 
 /* Pointer mangling is not yet supported for MIPS.  */