Messages in this thread | | | Date | Thu, 30 Apr 2015 09:59:49 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: perf: Fix callchain parse error with kernel tracepoint events |
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On Thu, Apr 30, 2015 at 02:50:05AM +0100, Hou Pengyang wrote: > On 2015/4/29 18:12, Will Deacon wrote: > > On Tue, Apr 28, 2015 at 02:20:48PM +0100, Hou Pengyang wrote: > >> diff --git a/arch/arm64/include/asm/perf_event.h b/arch/arm64/include/asm/perf_event.h > >> index d26d1d5..16a074f 100644 > >> --- a/arch/arm64/include/asm/perf_event.h > >> +++ b/arch/arm64/include/asm/perf_event.h > >> @@ -24,4 +24,20 @@ extern unsigned long perf_misc_flags(struct pt_regs *regs); > >> #define perf_misc_flags(regs) perf_misc_flags(regs) > >> #endif > >> > >> +#define perf_arch_fetch_caller_regs(regs, __ip) { \ > >> + unsigned long sp; \ > >> + __asm__ ("mov %[sp], sp\n" : [sp] "=r" (sp)); \ > >> + (regs)->pc = (__ip); \ > >> + __asm__ ( \ > >> + "str %[sp], %[_arm64_sp] \n\t" \ > >> + "str x29, %[_arm64_fp] \n\t" \ > >> + "mrs %[_arm64_cpsr], spsr_el1 \n\t" \ > >> + : [_arm64_sp] "=m" (regs->sp), \ > >> + [_arm64_fp] "=m" (regs->regs[29]), \ > >> + [_arm64_cpsr] "=r" (regs->pstate) \ > > > > Does this really all need to be in assembly code? Ideally we'd use something > > like __builtin_stack_pointer and __builtin_frame_pointer. That just leaves > > the CPSR, but given that it's (a) only used for user_mode_regs tests and (b) > > this macro is only used by ftrace, then we just set it to a static value > > indicating that we're at EL1. > > > > So I *think* we should be able to write this as three lines of C. > > > Hi, will, as you said, we can get fp by __builtin_frame_address() and > pstate by setting it to a static value. However, for sp, there isn't a > gcc builtin fuction like __builtin_stack_pointer, so assembly code is > needed. What's more, if CONFIG_FRAME_POINTER is close, can fp be got by > __builtin_frame_address()?
Ah yes, I forgot the history of __builtin_stack_pointer (I think the LLVM guys proposed it and it was rejected by GCC). Anyway, we can use current_stack_pointer() instead.
I don't think CONFIG_FRAME_POINTER is relevant here; if you don't have frame pointers then you won't be able to backtrace. The same issue happens with your proposed patch.
Will
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