[PATCH] i386: fix stack alignment for signal handlers This patches 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. Signed-off-by: Markus F.X.J. Oberhumer arch/i386/kernel/signal.c | 6 +++++- arch/x86_64/ia32/ia32_signal.c | 6 +++++- 2 files changed, 10 insertions(+), 2 deletions(-) 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 +338,11 @@ 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. 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 +425,11 @@ 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,