From bfe9a2cfe91a1c920f152ce5fd0a9ad74b3daf12 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Mon, 13 Oct 2014 19:41:38 +1100 Subject: powerpc: Reimplement __get_SP() as a function not a define 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later calls a function that is tail call optimised, we will pop the stack frame and the value returned by __get_SP() is no longer valid.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(). This also fixes an issue with perf_arch_fetch_caller_regs(). It currently unwinds the stack once, which will skip a valid stack frame on a leaf function. With the __get_SP() fixes in this patch, we never need to unwind the stack frame to get to the first interesting frame. We have to export __get_SP() because perf_arch_fetch_caller_regs() (which is used in modules) calls it from a header file. Reported-by: Li Zhong Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/reg.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/powerpc/include/asm/reg.h') diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h index fe3f9488f321..e539d7e71451 100644 --- a/arch/powerpc/include/asm/reg.h +++ b/arch/powerpc/include/asm/reg.h @@ -1265,8 +1265,7 @@ 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); -- cgit v1.2.3 From acf620ecf56cfc4edaffaf158250e128539cdd26 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Mon, 13 Oct 2014 19:41:39 +1100 Subject: powerpc: Rename __get_SP() to current_stack_pointer() Michael points out that __get_SP() is a pretty horrible function name. Let's give it a better name. Signed-off-by: Anton Blanchard Signed-off-by: Michael Ellerman --- arch/powerpc/include/asm/reg.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/powerpc/include/asm/reg.h') diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h index e539d7e71451..c998279bd85b 100644 --- a/arch/powerpc/include/asm/reg.h +++ b/arch/powerpc/include/asm/reg.h @@ -1265,7 +1265,7 @@ 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); -- cgit v1.2.3