x86: fix math_emu register frame access

do_device_not_available() is the handler for #NM and it declares that
it takes a unsigned long and calls math_emu(), which takes a long
argument and surprisingly expects the stack frame starting at the zero
argument would match struct math_emu_info, which isn't true regardless
of configuration in the current code.

This patch makes do_device_not_available() take struct pt_regs like
other exception handlers and initialize struct math_emu_info with
pointer to it and pass pointer to the math_emu_info to math_emulate()
like normal C functions do.  This way, unless gcc makes a copy of
struct pt_regs in do_device_not_available(), the register frame is
correctly accessed regardless of kernel configuration or compiler
used.

This doesn't fix all math_emu problems but it at least gets it
somewhat working.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 98c2d055284b..7932338d7cb3 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -896,7 +896,7 @@ asmlinkage void math_state_restore(void)
 EXPORT_SYMBOL_GPL(math_state_restore);
 
 #ifndef CONFIG_MATH_EMULATION
-asmlinkage void math_emulate(long arg)
+void math_emulate(struct math_emu_info *info)
 {
 	printk(KERN_EMERG
 		"math-emulation not enabled and no coprocessor found.\n");
@@ -906,16 +906,19 @@ asmlinkage void math_emulate(long arg)
 }
 #endif /* CONFIG_MATH_EMULATION */
 
-dotraplinkage void __kprobes
-do_device_not_available(struct pt_regs *regs, long error)
+dotraplinkage void __kprobes do_device_not_available(struct pt_regs regs)
 {
 #ifdef CONFIG_X86_32
 	if (read_cr0() & X86_CR0_EM) {
-		conditional_sti(regs);
-		math_emulate(0);
+		struct math_emu_info info = { };
+
+		conditional_sti(&regs);
+
+		info.regs = &regs;
+		math_emulate(&info);
 	} else {
 		math_state_restore(); /* interrupts still off */
-		conditional_sti(regs);
+		conditional_sti(&regs);
 	}
 #else
 	math_state_restore();