[PATCH] [4/5] Use asm stubs for 32bit sigreturn codes

Andi Kleen
2009-01-04T23:36:46Z

32bit sigreturn/rt_sigreturn currently uses some magic casting
with assumptions about the stack layout
to simulate call by reference for the pt_regs structure on the
stack. This is fragile, non standard and according to reports
breaks with LLVM at least. I suppose it could break in
future gcc versions too when their stack layout changes.

So instead of having this magic in C do it in small
assembler stubs similar to what x86-64 does (which
always passes a pointer to pt_regs for such functions)

This also leads to cleaner code.

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
arch/x86/kernel/entry_32.S | 10 ++++++++++
arch/x86/kernel/signal_32.c | 13 ++-----------
arch/x86/kernel/syscall_table_32.S | 4 ++--
3 files changed, 14 insertions(+), 13 deletions(-)

Index: linux-2.6.28-test/arch/x86/kernel/entry_32.S
===================================================================
--- linux-2.6.28-test.orig/arch/x86/kernel/entry_32.S 2008-11-06 20:26:33.000000000 +0100
+++ linux-2.6.28-test/arch/x86/kernel/entry_32.S 2009-01-02 16:01:06.000000000 +0100
@@ -1206,6 +1206,16 @@
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_TRACER */

+ENTRY(stub_sigreturn)
+ movl %esp,%eax
+ jmp sys_sigreturn
+END(stub_sigreturn)
+
+ENTRY(stub_rt_sigreturn)
+ movl %esp,%eax
+ jmp sys_rt_sigreturn
+END(stub_rt_sigreturn)
+
.section .rodata,"a"
#include "syscall_table_32.S"

Index: linux-2.6.28-test/arch/x86/kernel/signal_32.c
===================================================================
--- linux-2.6.28-test.orig/arch/x86/kernel/signal_32.c 2008-10-24 13:34:40.000000000 +0200
+++ linux-2.6.28-test/arch/x86/kernel/signal_32.c 2009-01-02 16:01:06.000000000 +0100
@@ -169,14 +169,12 @@
return err;
}

-asmlinkage unsigned long sys_sigreturn(unsigned long __unused)
+asmlinkage unsigned long sys_sigreturn(struct pt_regs *regs)
{
struct sigframe __user *frame;
- struct pt_regs *regs;
unsigned long ax;
sigset_t set;

- regs = (struct pt_regs *) &__unused;
frame = (struct sigframe __user *)(regs->sp - 8);

if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
@@ -212,7 +210,7 @@
return 0;
}

-static long do_rt_sigreturn(struct pt_regs *regs)
+asmlinkage long sys_rt_sigreturn(struct pt_regs *regs)
{
struct rt_sigframe __user *frame;
unsigned long ax;
@@ -243,13 +241,6 @@
return 0;
}

-asmlinkage int sys_rt_sigreturn(unsigned long __unused)
-{
- struct pt_regs *regs = (struct pt_regs *)&__unused;
-
- return do_rt_sigreturn(regs);
-}
-
/*
* Set up a signal frame.
*/
Index: linux-2.6.28-test/arch/x86/kernel/syscall_table_32.S
===================================================================
--- linux-2.6.28-test.orig/arch/x86/kernel/syscall_table_32.S 2008-08-15 17:13:40.000000000 +0200
+++ linux-2.6.28-test/arch/x86/kernel/syscall_table_32.S 2009-01-02 16:01:06.000000000 +0100
@@ -118,7 +118,7 @@
.long sys_sysinfo
.long sys_ipc
.long sys_fsync
- .long sys_sigreturn
+ .long stub_sigreturn
.long sys_clone /* 120 */
.long sys_setdomainname
.long sys_newuname
@@ -172,7 +172,7 @@
.long sys_setresgid16 /* 170 */
.long sys_getresgid16
.long sys_prctl
- .long sys_rt_sigreturn
+ .long stub_rt_sigreturn
.long sys_rt_sigaction
.long sys_rt_sigprocmask /* 175 */
.long sys_rt_sigpending