[PATCH] i386: fix stack alignment for signal handlers

It seems that the current signal code always sets up a stack frame
so that signal handlers are run with a somewhat mis-aligned stack,
i.e. (esp % 8 == 4).

While this is not an i386 ABI requirement we really would like to have
at least a 8-byte alignment (e.g. when using doubles or other floating
point stuff). Furthermore, as recent gcc versions default to
-mpreferred-stack-boundary=4, this patch assures a 16-byte alignment.

Signed-off-by: Markus F.X.J. Oberhumer <markus@oberhumer.com>


Index: linux-2.6.git/arch/i386/kernel/signal.c
===================================================================
--- linux-2.6.git.orig/arch/i386/kernel/signal.c
+++ linux-2.6.git/arch/i386/kernel/signal.c
@@ -338,7 +338,7 @@
 		esp = (unsigned long) ka->sa.sa_restorer;
 	}
 
-	return (void __user *)((esp - frame_size) & -8ul);
+	return (void __user *)((esp - frame_size) & -16ul);
 }
 
 /* These symbols are defined with the addresses in the vsyscall page.
@@ -354,7 +354,7 @@
 	int err = 0;
 	int usig;
 
-	frame = get_sigframe(ka, regs, sizeof(*frame));
+	frame = get_sigframe(ka, regs, sizeof(*frame)) - 4;
 
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		goto give_sigsegv;
@@ -444,7 +444,7 @@
 	int err = 0;
 	int usig;
 
-	frame = get_sigframe(ka, regs, sizeof(*frame));
+	frame = get_sigframe(ka, regs, sizeof(*frame)) - 4;
 
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		goto give_sigsegv;
Index: linux-2.6.git/arch/x86_64/ia32/ia32_signal.c
===================================================================
--- linux-2.6.git.orig/arch/x86_64/ia32/ia32_signal.c
+++ linux-2.6.git/arch/x86_64/ia32/ia32_signal.c
@@ -425,7 +425,7 @@
 		rsp = (unsigned long) ka->sa.sa_restorer;
 	}
 
-	return (void __user *)((rsp - frame_size) & -8UL);
+	return (void __user *)((rsp - frame_size) & -16UL);
 }
 
 int ia32_setup_frame(int sig, struct k_sigaction *ka,
@@ -434,7 +434,7 @@
 	struct sigframe __user *frame;
 	int err = 0;
 
-	frame = get_sigframe(ka, regs, sizeof(*frame));
+	frame = get_sigframe(ka, regs, sizeof(*frame)) - 4;
 
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		goto give_sigsegv;
@@ -527,7 +527,7 @@
 	struct rt_sigframe __user *frame;
 	int err = 0;
 
-	frame = get_sigframe(ka, regs, sizeof(*frame));
+	frame = get_sigframe(ka, regs, sizeof(*frame)) - 4;
 
 	if (!access_ok(VERIFY_WRITE, frame, sizeof(*frame)))
 		goto give_sigsegv;