[PATCH] x86_64: Move int 3 handler to debug stack and allow to increase it.

This
- switches the INT3 handler to run on an IST stack (to cope with
  breakpoints set by a kernel debugger on places where the kernel's
  %gs base hasn't been set up, yet); the IST stack used is shared with
  the INT1 handler's
[AK: this also allows setting a kprobe on the interrupt/exception entry
points]
- allows nesting of INT1/INT3 handlers so that one can, with a kernel
  debugger, debug (at least) the user-mode portions of the INT1/INT3
  handling; the nesting isn't actively enabled here since a kernel-
  debugger-free kernel doesn't need it

Signed-Off-By: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 22 insertions, 4 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index bd21ebafaf66..28b3c8e6b044 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -673,7 +673,10 @@ ENTRY(spurious_interrupt)
 
         /* error code is on the stack already */
         /* handle NMI like exceptions that can happen everywhere */
-        .macro paranoidentry sym
+#ifndef DEBUG_IST
+# define DEBUG_IST 0
+#endif
+        .macro paranoidentry sym, ist=0
         SAVE_ALL
         cld
         movl $1,%ebx
@@ -683,10 +686,20 @@ ENTRY(spurious_interrupt)
         js    1f
         swapgs
         xorl  %ebx,%ebx
-1:      movq %rsp,%rdi
+1:
+        .if \ist
+        movq    %gs:pda_data_offset, %rbp
+        .endif
+        movq %rsp,%rdi
         movq ORIG_RAX(%rsp),%rsi
         movq $-1,ORIG_RAX(%rsp)
+        .if \ist
+        subq    $EXCEPTION_STACK_SIZE, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)
+        .endif
         call \sym
+        .if \ist
+        addq    $EXCEPTION_STACK_SIZE, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)
+        .endif
         cli
         .endm
         
@@ -904,7 +917,7 @@ KPROBE_ENTRY(debug)
         INTR_FRAME
         pushq $0
         CFI_ADJUST_CFA_OFFSET 8         
-        paranoidentry do_debug
+        paranoidentry do_debug, DEBUG_IST
         jmp paranoid_exit
         CFI_ENDPROC
         .previous .text
@@ -959,7 +972,12 @@ paranoid_schedule:
         CFI_ENDPROC
 
 KPROBE_ENTRY(int3)
-        zeroentry do_int3       
+        INTR_FRAME
+        pushq $0
+        CFI_ADJUST_CFA_OFFSET 8
+        paranoidentry do_int3, DEBUG_IST
+        jmp paranoid_exit
+        CFI_ENDPROC
         .previous .text
 
 ENTRY(overflow)