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tracing, x86: fix fixup section to return to original code 

Impact: fix to prevent a kernel crash on fault

If for some reason the pointer to the parent function on the
stack takes a fault, the fix up code will not return back to
the original faulting code. This can lead to unpredictable
results and perhaps even a kernel panic.

A fault should not happen, but if it does, we should simply
disable the tracer, warn, and continue running the kernel.
It should not lead to a kernel crash.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
This commit is contained in:
Steven Rostedt 2009-02-10 13:07:13 -05:00
parent acd895795d
commit e3944bfac9
1 changed files with 5 additions and 3 deletions
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8
arch/x86/kernel/ftrace.c
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@ -491,13 +491,15 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
"1: " _ASM_MOV " (%[parent_old]), %[old]\n"
"2: " _ASM_MOV " %[return_hooker], (%[parent_replaced])\n"
" movl $0, %[faulted]\n"
"3:\n"
".section .fixup, \"ax\"\n"
"3: movl $1, %[faulted]\n"
"4: movl $1, %[faulted]\n"
" jmp 3b\n"
".previous\n"
_ASM_EXTABLE(1b, 3b)
_ASM_EXTABLE(2b, 3b)
_ASM_EXTABLE(1b, 4b)
_ASM_EXTABLE(2b, 4b)
: [parent_replaced] "=r" (parent), [old] "=r" (old),
[faulted] "=r" (faulted)