Messages in this thread Patch in this message | | | Date | Tue, 13 Sep 2005 22:55:15 +0200 | From | "Markus F.X.J. Oberhumer" <> | Subject | [PATCH] i386: fix stack alignment for signal handlers |
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[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>
Please try the small attached user-space test program and please also carefully review the patch below - I don't do much kernel hacking...
~Markus
-- Markus Oberhumer, <markus@oberhumer.com>, http://www.oberhumer.com/
/* test signal stack alignment (sigframe) */ /* Markus F.X.J. Oberhumer <markus@oberhumer.com> */
#include <signal.h> #include <stdio.h> #include <stdlib.h> #include <time.h>
volatile unsigned long signal_sp = 0;
#if defined(__x86_64__) /* amd64: signal stack is properly aligned */ asm( ".text\n .align 16\n" "my_sighandler:\n" "lea 8(%rsp),%rax\n" "movq %rax,(signal_sp)\n" "retq\n" ); #elif defined(__i386__) /* i386: signal stack is always mis-aligned to 4-bytes */ asm( ".text\n .align 16\n" "my_sighandler:\n" "lea 4(%esp),%eax\n" "movl %eax,(signal_sp)\n" "ret\n" ); #else #error "arch not supported - please insert your code here" #endif
#if defined(__cplusplus) extern "C" #endif void my_sighandler(int);
int main() { int signo = SIGUSR1;
#if 1 /* randomize stack */ void * volatile dummy = NULL; srand((unsigned)clock() % RAND_MAX); dummy = __builtin_alloca(rand() % 2048ul); #endif
signal_sp = 0; signal(signo, my_sighandler); raise(signo); printf("sp = 0x%lx alignment = %lu\n", signal_sp, signal_sp & 15); if (signal_sp & 15) printf(" error: signal stack not aligned\n");
return 0; }
/* vim:set ts=4 et: */
[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;
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