Commit f79290b6 authored by Steven Rostedt (Red Hat)'s avatar Steven Rostedt (Red Hat) Committed by Luis Henriques

ftrace/x86: Add frames pointers to trampoline as necessary

commit 9960efeb upstream.

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
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 4240408c
......@@ -45,6 +45,39 @@ END(function_hook)
#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)
/* Check if tracing was disabled (quick check) */
cmpl $0, function_trace_stop
......@@ -54,9 +87,13 @@ ENTRY(ftrace_caller)
/* 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
ftrace_return:
......@@ -104,9 +141,13 @@ 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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