Li Zhong points out an issue with our current __get_SP()
implementation. If ftrace function tracing is enabled (ie -pg
profiling using _mcount) we spill a stack frame on 64bit all the
time.
If a function calls __get_SP() and later calls a function that is
tail call optimised, we will pop the stack frame and the value
returned by __get_SP() is no longer valid. An example from Li can
be found in save_stack_trace -> save_context_stack:
c0000000000432c0 <.save_stack_trace>:
c0000000000432c0: mflr r0
c0000000000432c4: std r0,16(r1)
c0000000000432c8: stdu r1,-128(r1) <-- stack frame for _mcount
c0000000000432cc: std r3,112(r1)
c0000000000432d0: bl <._mcount>
c0000000000432d4: nop
c0000000000432d8: mr r4,r1 <-- __get_SP()
c0000000000432dc: ld r5,632(r13)
c0000000000432e0: ld r3,112(r1)
c0000000000432e4: li r6,1
c0000000000432e8: addi r1,r1,128 <-- pop stack frame
c0000000000432ec: ld r0,16(r1)
c0000000000432f0: mtlr r0
c0000000000432f4: b <.save_context_stack> <-- tail call optimized
save_context_stack ends up with a stack pointer below the current
one, and it is likely to be scribbled over.
Fix this by making __get_SP() a function which returns the
callers stack frame. Also replace inline assembly which grabs
the stack pointer in save_stack_trace and show_stack with
__get_SP().
Reported-by: Li Zhong <zh...@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <an...@samba.org>
---
arch/powerpc/include/asm/reg.h | 3 +--
arch/powerpc/kernel/misc.S | 4 ++++
arch/powerpc/kernel/process.c | 2 +-
arch/powerpc/kernel/stacktrace.c | 2 +-
4 files changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 0c05059..0f973c0 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1264,8 +1264,7 @@ static inline unsigned long mfvtb (void)
#define proc_trap() asm volatile("trap")
-#define __get_SP() ({unsigned long sp; \
- asm volatile("mr %0,1": "=r" (sp)); sp;})
+extern unsigned long __get_SP(void);
extern unsigned long scom970_read(unsigned int address);
extern void scom970_write(unsigned int address, unsigned long value);
diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S
index 7ce26d4..120deb7 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -114,3 +114,7 @@ _GLOBAL(longjmp)
mtlr r0
mr r3,r4
blr
+
+_GLOBAL(__get_SP)
+ PPC_LL r3,0(r1)
+ blr
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index aa1df89..3cc6439 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1545,7 +1545,7 @@ void show_stack(struct task_struct *tsk, unsigned long
*stack)
tsk = current;
if (sp == 0) {
if (tsk == current)
- asm("mr %0,1" : "=r" (sp));
+ sp = __get_SP();
else
sp = tsk->thread.ksp;
}
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 3d30ef1..7f65bae 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -50,7 +50,7 @@ void save_stack_trace(struct stack_trace *trace)
{
unsigned long sp;
- asm("mr %0,1" : "=r" (sp));
+ sp = __get_SP();
save_context_stack(trace, sp, current, 1);
}
--
1.9.1
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