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SubjectRe: [PATCH 1/2] ftrace/x86: Add frames pointers to trampoline as necessary
On Tue, 18 Nov 2014, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
>
> When CONFIG_FRAME_POINTERS are enabled, it is required that the
> ftrace_caller and ftrace_regs_caller trampolines set up frame pointers
> otherwise a stack trace from a function call wont print the functions
> that called the trampoline. This is due to a check in
> __save_stack_address():
>
> #ifdef CONFIG_FRAME_POINTER
> if (!reliable)
> return;
> #endif
>
> The "reliable" variable is only set if the function address is equal to
> contents of the address before the address the frame pointer register
> points to. If the frame pointer is not set up for the ftrace caller
> then this will fail the reliable test. It will miss the function that
> called the trampoline. Worse yet, if fentry is used (gcc 4.6 and
> beyond), it will also miss the parent, as the fentry is called before
> the stack frame is set up. That means the bp frame pointer points
> to the stack of just before the parent function was called.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: x86@kernel.org
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Shouldn't this be tagged stable?

Acked-by: Thomas Gleixner <tglx@linutronix.de>

> ---
> arch/x86/kernel/mcount_64.S | 41 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
> diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
> index 42f0cdd20baf..35a793fa4bba 100644
> --- a/arch/x86/kernel/mcount_64.S
> +++ b/arch/x86/kernel/mcount_64.S
> @@ -47,14 +47,51 @@ GLOBAL(\trace_label)
> #endif
> .endm
>
> +#ifdef CONFIG_FRAME_POINTER
> +/*
> + * Stack traces will stop at the ftrace trampoline if the frame pointer
> + * is not set up properly. If fentry is used, we need to save a frame
> + * pointer for the parent as well as the function traced, because the
> + * fentry is called before the stack frame is set up, where as mcount
> + * is called afterward.
> + */
> +.macro create_frame parent rip
> +#ifdef CC_USING_FENTRY
> + pushq \parent
> + pushq %rbp
> + movq %rsp, %rbp
> +#endif
> + pushq \rip
> + pushq %rbp
> + movq %rsp, %rbp
> +.endm
> +
> +.macro restore_frame
> +#ifdef CC_USING_FENTRY
> + addq $16, %rsp
> +#endif
> + popq %rbp
> + addq $8, %rsp
> +.endm
> +#else
> +.macro create_frame parent rip
> +.endm
> +.macro restore_frame
> +.endm
> +#endif /* CONFIG_FRAME_POINTER */
> +
> ENTRY(ftrace_caller)
> ftrace_caller_setup ftrace_caller_op_ptr
> /* regs go into 4th parameter (but make it NULL) */
> movq $0, %rcx
>
> + create_frame %rsi, %rdi
> +
> GLOBAL(ftrace_call)
> call ftrace_stub
>
> + restore_frame
> +
> MCOUNT_RESTORE_FRAME
>
> /*
> @@ -105,9 +142,13 @@ ENTRY(ftrace_regs_caller)
> /* regs go into 4th parameter */
> leaq (%rsp), %rcx
>
> + create_frame %rsi, %rdi
> +
> GLOBAL(ftrace_regs_call)
> call ftrace_stub
>
> + restore_frame
> +
> /* Copy flags back to SS, to restore them */
> movq EFLAGS(%rsp), %rax
> movq %rax, SS(%rsp)
> --
> 2.1.1
>
>
>


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