From: "Steven Rostedt (Red Hat)" 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 Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Signed-off-by: Steven Rostedt --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/