I found stack trace couldn't be saved sometimes. After some
investigation, it seems that when function trace is enabled,
void save_stack_trace(struct stack_trace *trace)
{
unsigned long sp;
asm("mr %0,1" : "=r" (sp));
save_context_stack(trace, sp, current, 1);
}
is compiled into:
c0000000000432c0 <.save_stack_trace>:
c0000000000432c0: 7c 08 02 a6 mflr r0
c0000000000432c4: f8 01 00 10 std r0,16(r1)
c0000000000432c8: f8 21 ff 81 stdu r1,-128(r1)
c0000000000432cc: f8 61 00 70 std r3,112(r1)
c0000000000432d0: 4b fc 77 bd bl c00000000000aa8c
<._mcount>
c0000000000432d4: 60 00 00 00 nop
c0000000000432d8: 7c 24 0b 78 mr r4,r1
c0000000000432dc: e8 ad 02 78 ld r5,632(r13)
c0000000000432e0: e8 61 00 70 ld r3,112(r1)
c0000000000432e4: 38 c0 00 01 li r6,1
c0000000000432e8: 38 21 00 80 addi r1,r1,128
c0000000000432ec: e8 01 00 10 ld r0,16(r1)
c0000000000432f0: 7c 08 03 a6 mtlr r0
c0000000000432f4: 4b ff fe 5c b c000000000043150
<.save_context_stack>
c0000000000432f8: 60 00 00 00 nop
c0000000000432fc: 60 42 00 00 ori r2,r2,0
new stack frame -128(r1) is created to call ._mcount, and this new r1 is
copied into sp as the stack pointer, which then could be overwritten by
save_context_stack's prolog.
I don't know how to specify in C that the embedded asm be compiled after
r1 being added back to the original value. But as a workaround, maybe we
could move this embedded asm into save_context_stack().
Signed-off-by: Li Zhong <zh...@linux.vnet.ibm.com>
---
arch/powerpc/kernel/stacktrace.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 3d30ef1..5c0b461 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -22,6 +22,9 @@
static void save_context_stack(struct stack_trace *trace, unsigned long sp,
struct task_struct *tsk, int savesched)
{
+ if (tsk == current)
+ asm("mr %0,1" : "=r" (sp));
+
for (;;) {
unsigned long *stack = (unsigned long *) sp;
unsigned long newsp, ip;
@@ -48,11 +51,7 @@ static void save_context_stack(struct stack_trace *trace,
unsigned long sp,
void save_stack_trace(struct stack_trace *trace)
{
- unsigned long sp;
-
- asm("mr %0,1" : "=r" (sp));
-
- save_context_stack(trace, sp, current, 1);
+ save_context_stack(trace, 0, current, 1);
}
EXPORT_SYMBOL_GPL(save_stack_trace);
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