[PATCH] i386: fix stack alignment for signal handlers

This fixes the setup of the alignment of the signal frame, so that all
signal handlers are run with a properly aligned stack frame.

The current code "over-aligns" the stack pointer so that the stack frame
is effectively always mis-aligned by 4 bytes.  But what we really want
is that on function entry ((sp + 4) & 15) == 0, which matches what would
happen if the stack were aligned before a "call" instruction.
Signed-off-by: Markus F.X.J. Oberhumer <markus@oberhumer.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/signal.c

@@ -338,7 +338,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
 		esp = (unsigned long) ka->sa.sa_restorer;
 	}
 
-	return (void __user *)((esp - frame_size) & -8ul);
+	esp -= frame_size;
+	/* Align the stack pointer according to the i386 ABI,
+	 * i.e. so that on function entry ((sp + 4) & 15) == 0. */
+	esp = ((esp + 4) & -16ul) - 4;
+	return (void __user *) esp;
 }
 
 /* These symbols are defined with the addresses in the vsyscall page.

arch/x86_64/ia32/ia32_signal.c

@@ -425,7 +425,11 @@ get_sigframe(struct k_sigaction *ka, struct pt_regs * regs, size_t frame_size)
 		rsp = (unsigned long) ka->sa.sa_restorer;
 	}
 
-	return (void __user *)((rsp - frame_size) & -8UL);
+	rsp -= frame_size;
+	/* Align the stack pointer according to the i386 ABI,
+	 * i.e. so that on function entry ((sp + 4) & 15) == 0. */
+	rsp = ((rsp + 4) & -16ul) - 4;
+	return (void __user *) rsp;
 }
 
 int ia32_setup_frame(int sig, struct k_sigaction *ka,