Commit 9960efeb authored Nov 18, 2014 by Steven Rostedt (Red Hat) Committed by Steven Rostedt Nov 19, 2014

ftrace/x86: Add frames pointers to trampoline as necessary

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.

Link: http://lkml.kernel.org/r/20141119034829.355440340@goodmis.org



Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: stable@vger.kernel.org # 3.7+
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent a9ce7c36

arch/x86/kernel/mcount_64.S

+41 −0

Original line number	Diff line number	Diff line
		@@ -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)

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