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* [PATCH] powerpc: Reimplement __get_SP() as a function not a define
@ 2014-10-01  5:10 Anton Blanchard
  2014-10-01  7:11 ` [PATCH] powerpc: Rename __get_SP() to current_stack_pointer() Anton Blanchard
  2014-10-08  8:47 ` [PATCH] powerpc: Reimplement __get_SP() as a function not a define Li Zhong
  0 siblings, 2 replies; 3+ messages in thread
From: Anton Blanchard @ 2014-10-01  5:10 UTC (permalink / raw)
  To: zhong, benh, paulus, mpe; +Cc: linuxppc-dev

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returned by __get_SP() is no longer valid.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 <zhong@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <anton@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

^ permalink raw reply related	[flat|nested] 3+ messages in thread
* [PATCH] powerpc: Rename __get_SP() to current_stack_pointer()
  2014-10-01  5:10 [PATCH] powerpc: Reimplement __get_SP() as a function not a define Anton Blanchard
@ 2014-10-01  7:11 ` Anton Blanchard
  2014-10-08  8:47 ` [PATCH] powerpc: Reimplement __get_SP() as a function not a define Li Zhong
  1 sibling, 0 replies; 3+ messages in thread
From: Anton Blanchard @ 2014-10-01  7:11 UTC (permalink / raw)
  To: zhong, benh, paulus, mpe; +Cc: linuxppc-dev

Michael points out that __get_SP() is a pretty horrible
function name. Let's give it a better name.

Signed-off-by: Anton Blanchard <anton@samba.org>
---
 arch/powerpc/include/asm/perf_event.h | 2 +-
 arch/powerpc/include/asm/reg.h        | 2 +-
 arch/powerpc/kernel/irq.c             | 2 +-
 arch/powerpc/kernel/misc.S            | 2 +-
 arch/powerpc/kernel/process.c         | 2 +-
 arch/powerpc/kernel/stacktrace.c      | 2 +-
 6 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/perf_event.h b/arch/powerpc/include/asm/perf_event.h
index 0bb2372..fc53598 100644
--- a/arch/powerpc/include/asm/perf_event.h
+++ b/arch/powerpc/include/asm/perf_event.h
@@ -34,7 +34,7 @@
 	do {							\
 		(regs)->result = 0;				\
 		(regs)->nip = __ip;				\
-		(regs)->gpr[1] = *(unsigned long *)__get_SP();	\
+		(regs)->gpr[1] = *(unsigned long *)current_stack_pointer(); \
 		asm volatile("mfmsr %0" : "=r" ((regs)->msr));	\
 	} while (0)
 #endif
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index 0f973c0..d8974b5 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/arch/powerpc/include/asm/reg.h
@@ -1264,7 +1264,7 @@ static inline unsigned long mfvtb (void)
 
 #define proc_trap()	asm volatile("trap")
 
-extern unsigned long __get_SP(void);
+extern unsigned long current_stack_pointer(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/irq.c b/arch/powerpc/kernel/irq.c
index 8eb857f..c143835 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -466,7 +466,7 @@ static inline void check_stack_overflow(void)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	long sp;
 
-	sp = __get_SP() & (THREAD_SIZE-1);
+	sp = current_stack_pointer() & (THREAD_SIZE-1);
 
 	/* check for stack overflow: is there less than 2KB free? */
 	if (unlikely(sp < (sizeof(struct thread_info) + 2048))) {
diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S
index 120deb7..0d43219 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -115,6 +115,6 @@ _GLOBAL(longjmp)
 	mr	r3,r4
 	blr
 
-_GLOBAL(__get_SP)
+_GLOBAL(current_stack_pointer)
 	PPC_LL	r3,0(r1)
 	blr
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 3cc6439..923cd2d 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)
-			sp = __get_SP();
+			sp = current_stack_pointer();
 		else
 			sp = tsk->thread.ksp;
 	}
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 7f65bae..ea43a34 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;
 
-	sp = __get_SP();
+	sp = current_stack_pointer();
 
 	save_context_stack(trace, sp, current, 1);
 }
-- 
1.9.1

^ permalink raw reply related	[flat|nested] 3+ messages in thread
* Re: [PATCH] powerpc: Reimplement __get_SP() as a function not a define
  2014-10-01  5:10 [PATCH] powerpc: Reimplement __get_SP() as a function not a define Anton Blanchard
  2014-10-01  7:11 ` [PATCH] powerpc: Rename __get_SP() to current_stack_pointer() Anton Blanchard
@ 2014-10-08  8:47 ` Li Zhong
  1 sibling, 0 replies; 3+ messages in thread
From: Li Zhong @ 2014-10-08  8:47 UTC (permalink / raw)
  To: Anton Blanchard; +Cc: paulus, linuxppc-dev

On 三, 2014-10-01 at 15:10 +1000, Anton Blanchard wrote:
> 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 <zhong@linux.vnet.ibm.com>
> Signed-off-by: Anton Blanchard <anton@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);

It seems that some module code is using __get_SP, e.g. xfs in the
example below:
ERROR: ".__get_SP" [fs/xfs/xfs.ko] undefined!

Maybe we need export this symbol in arch/powerpc/kernel/ppc_ksyms.c? 

diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c
index 48d17d6f..eebd4e4 100644
--- a/arch/powerpc/kernel/ppc_ksyms.c
+++ b/arch/powerpc/kernel/ppc_ksyms.c
@@ -207,3 +207,5 @@ EXPORT_SYMBOL_GPL(mmu_psize_defs);
 #ifdef CONFIG_EPAPR_PARAVIRT
 EXPORT_SYMBOL(epapr_hypercall_start);
 #endif
+
+EXPORT_SYMBOL(__get_SP);

With the above compiling error fixed, this patch solved the SP issue I saw, so 

Tested-by: Li Zhong <zhong@linux.vnet.ibm.com>

>  
>  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);
>  }

^ permalink raw reply related	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2014-10-08  8:48 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2014-10-01  5:10 [PATCH] powerpc: Reimplement __get_SP() as a function not a define Anton Blanchard
2014-10-01  7:11 ` [PATCH] powerpc: Rename __get_SP() to current_stack_pointer() Anton Blanchard
2014-10-08  8:47 ` [PATCH] powerpc: Reimplement __get_SP() as a function not a define Li Zhong

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