Make sure no code in ld.so uses xmm/ymm registers on x86-64.

This patch introduces a test to make sure no function modifies the
xmm/ymm registers.  With the exception of the auditing functions.

The test is probably too pessimistic.  All code linked into ld.so
is checked.  Perhaps at some point the callgraph starting from
_dl_fixup and _dl_profile_fixup is checked and we can start using
faster SSE-using functions in parts of ld.so.

1 files changed, 28 insertions, 0 deletions

diff --git a/sysdeps/x86_64/rtld-strcmp.S b/sysdeps/x86_64/rtld-strcmp.S
new file mode 100644
index 0000000000..a25535c161
--- /dev/null
+++ b/sysdeps/x86_64/rtld-strcmp.S
@@ -0,0 +1,28 @@
+#include <sysdep.h>
+#include "asm-syntax.h"
+#include "bp-sym.h"
+#include "bp-asm.h"
+
+#ifndef LABEL
+#define LABEL(l) L(l)
+#endif
+
+	.text
+ENTRY (BP_SYM (STRCMP))
+/* Simple version since we can't use SSE registers in ld.so.  */
+L(oop):	movb	(%rdi), %al
+	cmpb	(%rsi), %al
+	jne	L(neq)
+	incq	%rdi
+	incq	%rsi
+	testb	%al, %al
+	jnz	L(oop)
+
+	xorl	%eax, %eax
+	ret
+
+L(neq):	movl	$1, %eax
+	movl	$-1, %ecx
+	cmovbl	%ecx, %eax
+	ret
+END (BP_SYM (STRCMP))