[PATCH 3.16.y-ckt 036/216] ftrace/x86: Add frames pointers to trampoline as necessary

Luis Henriques
2015-01-12T18:28:42Z

From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

commit 9960efeb80f73bd073483dab0855ee0ddc27085c 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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
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 c050a0153168..0b15b5b3957c 100644
--- a/arch/x86/kernel/mcount_64.S
+++ b/arch/x86/kernel/mcount_64.S
@@ -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)
--
2.1.4