On Oct 8, 2015, at 7:01 PM, AKASHI Takahiro wrote:
Hi Akashi,
> On arm64, no PC values returned by save_stack_trace() will match to LR
> values saved in stack frames on a stack after the following commit:
> commit e306dfd06fcb ("ARM64: unwind: Fix PC calculation")
> As a result, the output from stack tracer will be messed up.
>
> This patch introduces an arch-defined macro, FTRACE_STACK_FRAME_OFFSET,
> so that check_stack() can handle this case correctly.
>
> Signed-off-by: AKASHI Takahiro <takahiro.aka...@linaro.org>
> ---
> arch/arm64/include/asm/ftrace.h | 5 +++--
> arch/arm64/kernel/stacktrace.c | 7 ++++---
> include/linux/ftrace.h | 7 +++++++
> kernel/trace/trace_stack.c | 5 +++--
> 4 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> index c5534fa..2b43e20 100644
> --- a/arch/arm64/include/asm/ftrace.h
> +++ b/arch/arm64/include/asm/ftrace.h
> @@ -13,8 +13,9 @@
>
> #include <asm/insn.h>
>
> -#define MCOUNT_ADDR ((unsigned long)_mcount)
> -#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
> +#define MCOUNT_ADDR ((unsigned long)_mcount)
> +#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
> +#define FTRACE_STACK_FRAME_OFFSET AARCH64_INSN_SIZE
>
> #ifndef __ASSEMBLY__
> #include <linux/compat.h>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 407991b..bc0689a 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -20,6 +20,7 @@
> #include <linux/sched.h>
> #include <linux/stacktrace.h>
>
> +#include <asm/insn.h>
> #include <asm/stacktrace.h>
>
> /*
> @@ -49,10 +50,10 @@ int notrace unwind_frame(struct stackframe *frame)
> frame->sp = fp + 0x10;
> frame->fp = *(unsigned long *)(fp);
> /*
> - * -4 here because we care about the PC at time of bl,
> - * not where the return will go.
> + * decrement PC by AARCH64_INSN_SIZE here because we care about
> + * the PC at time of bl, not where the return will go.
> */
> - frame->pc = *(unsigned long *)(fp + 8) - 4;
> + frame->pc = *(unsigned long *)(fp + 8) - AARCH64_INSN_SIZE;
>
> return 0;
> }
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 6cd8c0e..d77b195 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -263,6 +263,13 @@ static inline void ftrace_kill(void) { }
> #endif /* CONFIG_FUNCTION_TRACER */
>
> #ifdef CONFIG_STACK_TRACER
> +/*
> + * the offset value to add to return address from save_stack_trace()
> + */
> +#ifndef FTRACE_STACK_FRAME_OFFSET
> +#define FTRACE_STACK_FRAME_OFFSET 0
> +#endif
> +
> extern int stack_tracer_enabled;
> int
> stack_trace_sysctl(struct ctl_table *table, int write,
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index b746399..30521ea 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -105,7 +105,7 @@ check_stack(unsigned long ip, unsigned long *stack)
>
> /* Skip over the overhead of the stack tracer itself */
> for (i = 0; i < max_stack_trace.nr_entries; i++) {
> - if (stack_dump_trace[i] == ip)
> + if ((stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET) == ip)
> break;
> }
>
> @@ -133,7 +133,8 @@ check_stack(unsigned long ip, unsigned long *stack)
> for (; p < top && i < max_stack_trace.nr_entries; p++) {
> if (stack_dump_trace[i] == ULONG_MAX)
> break;
> - if (*p == stack_dump_trace[i]) {
> + if (*p == (stack_dump_trace[i]
> + + FTRACE_STACK_FRAME_OFFSET)) {
> stack_dump_trace[x] = stack_dump_trace[i++];
> this_size = stack_dump_index[x++] =
> (top - p) * sizeof(unsigned long);
> --
This change is always on my tree for IRQ stack feature development. It makes
stack_trace prints out useful info although it can't give an accurate data.
I believe this hunk helps to figure out max stack depth context.
Acked-by: Jungseok Lee <jungseokle...@gmail.com>
Thanks!
Best Regards
Jungseok Lee--
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