From a879cbbb34cbecfa9707fbb6e5a00c503ac1ecb9 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@ppc970.osdl.org>
Date: Fri, 29 Apr 2005 09:38:44 -0700
Subject: x86: make traps on 'iret' be debuggable in user space

This makes a trap on the 'iret' that returns us to user space
cause a nice clean SIGSEGV, instead of just a hard (and silent)
exit.

That way a debugger can actually try to see what happened, and
we also properly notify everybody who might be interested about
us being gone.

This loses the error code, but tells the debugger what happened
with ILL_BADSTK in the siginfo.

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 3c73dc8..fe1918c 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -260,11 +260,9 @@ restore_nocheck:
 .section .fixup,"ax"
 iret_exc:
 	sti
-	movl $__USER_DS, %edx
-	movl %edx, %ds
-	movl %edx, %es
-	movl $11,%eax
-	call do_exit
+	pushl $0			# no error code
+	pushl $do_iret_error
+	jmp error_code
 .previous
 .section __ex_table,"a"
 	.align 4
diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index 6c0e383..d708194 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -451,6 +451,7 @@ DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
 DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
 DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
+DO_ERROR_INFO(32, SIGSEGV, "iret exception", iret_error, ILL_BADSTK, 0)
 
 fastcall void do_general_protection(struct pt_regs * regs, long error_code)
 {
-- 
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