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authorUlrich Drepper <drepper@redhat.com>2002-10-16 04:39:59 +0000
committerUlrich Drepper <drepper@redhat.com>2002-10-16 04:39:59 +0000
commit708296036c9753b9d08cba905a398f11095101c9 (patch)
tree0528b6cd748fa6113aa555b72e32dd7d3a4c8eff
parente3ea7124d78b8936305ee42215c7a862bbc29691 (diff)
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Optimize for kernels which are known to have the vfork syscall. Don't confuse the CPUs branch prediction unit by jumping to the return address.
-rw-r--r--sysdeps/unix/sysv/linux/i386/vfork.S29
1 files changed, 20 insertions, 9 deletions
diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S
index 6f7477e89d..59657e49c0 100644
--- a/sysdeps/unix/sysv/linux/i386/vfork.S
+++ b/sysdeps/unix/sysv/linux/i386/vfork.S
@@ -1,4 +1,4 @@
-/* Copyright (C) 1999 Free Software Foundation, Inc.
+/* Copyright (C) 1999, 2002 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Andreas Schwab <schwab@gnu.org>.
 
@@ -20,6 +20,7 @@
 #include <sysdep.h>
 #define _ERRNO_H	1
 #include <bits/errno.h>
+#include <kernel-features.h>
 
 /* Clone the calling process, but without copying the whole address space.
    The calling process is suspended until the new process exits or is
@@ -36,22 +37,32 @@ ENTRY (__vfork)
 	/* Stuff the syscall number in EAX and enter into the kernel.  */
 	movl	$SYS_ify (vfork), %eax
 	int	$0x80
+
+	/* Jump to the return PC.  Don't jump directly since this
+	   disturbs the branch target cache.  Instead push the return
+	   address back on the stack.  */
+	pushl	%ecx
+
 	cmpl	$-4095, %eax
-	jae	.Lerror		/* Branch forward if it failed.  */
+	/* Branch forward if it failed.  */
+# ifdef __ASSUME_VFORK_SYSCALL
+	jae	SYSCALL_ERROR_LABEL
+.Lpseudo_end:
+# else
+	jae	.Lerror
+# endif
 
-	/* Jump to the return PC.  */
-	jmp	*%ecx
+	ret
 
+# ifndef __ASSUME_VFORK_SYSCALL
 .Lerror:
-	/* Push back the return PC.  */
-	pushl	%ecx
-
 	/* Check if vfork syscall is known at all.  */
 	cmpl	$-ENOSYS, %eax
 	jne	SYSCALL_ERROR_LABEL
-
+# endif
 #endif
 
+#ifndef __ASSUME_VFORK_SYSCALL
 	/* If we don't have vfork, fork is close enough.  */
 
 	movl	$SYS_ify (fork), %eax
@@ -60,7 +71,7 @@ ENTRY (__vfork)
 	jae	SYSCALL_ERROR_LABEL
 .Lpseudo_end:
 	ret
-
+#endif
 PSEUDO_END (__vfork)
 
 weak_alias (__vfork, vfork)