Currently GCC generates highly sub-optimal code on architectures where
the calling convention prefers registers for argument passing. This is
GCC PR100955. While it's technically a missed-optimization in GCC, it
seems not trivial to fix (I've not seen any compiler which can optimize
this properly yet).
As the generic Linux syscall actually uses a fixed number of arguments,
we can avoid va_list if possible and make the compiler do right thing.
Add a macro __ASSUME_SYSCALL_NAMED_WORKS which should be defined if the
calling convention treats (x named arguments + y variable arguments)
exactly same as (x + y) named arguments, while each argument is either
an integer of which the width is less than or equal to "long" or a
pointer; and each argument can be fetched from the same register or the
same offset from the stack pointer no matter how many (maybe zero)
arguments are passed after it.
---
sysdeps/unix/sysv/linux/syscall.c | 35 ++++++++++++++++++++++++-------
1 file changed, 27 insertions(+), 8 deletions(-)
@@ -16,9 +16,33 @@
License along with the GNU C Library. If not, see
<https://www.gnu.org/licenses/>. */
-#include <stdarg.h>
#include <sysdep.h>
+#ifndef __ASSUME_SYSCALL_NAMED_WORKS
+#include <stdarg.h>
+#endif
+
+static inline long int
+__syscall (long int number, long int a0, long int a1, long int a2, long int a3,
+ long int a4, long int a5)
+{
+ long int r = INTERNAL_SYSCALL_NCS_CALL (number, a0, a1, a2, a3, a4, a5);
+ if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (r)))
+ {
+ __set_errno (-r);
+ return -1;
+ }
+ return r;
+}
+
+#ifdef __ASSUME_SYSCALL_NAMED_WORKS
+long int
+syscall (long int number, long int a0, long int a1, long int a2, long int a3,
+ long int a4, long int a5)
+{
+ return __syscall (number, a0, a1, a2, a3, a4, a5);
+}
+#else
long int
syscall (long int number, ...)
{
@@ -33,11 +57,6 @@ syscall (long int number, ...)
long int a5 = va_arg (args, long int);
va_end (args);
- long int r = INTERNAL_SYSCALL_NCS_CALL (number, a0, a1, a2, a3, a4, a5);
- if (__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (r)))
- {
- __set_errno (-r);
- return -1;
- }
- return r;
+ return __syscall (number, a0, a1, a2, a3, a4, a5);
}
+#endif