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x86/ftrace: Fix ORC unwinding from ftrace handlers

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Steven Rostedt discovered that the ftrace stack tracer is broken when
it's used with the ORC unwinder.  The problem is that objtool is
instructed by the Makefile to ignore the ftrace_64.S code, so it doesn't
generate any ORC data for it.

Fix it by making the asm code objtool-friendly:

- Objtool doesn't like the fact that save_mcount_regs pushes RBP at the
  beginning, but it's never restored (directly, at least).  So just skip
  the original RBP push, which is only needed for frame pointers anyway.

- Annotate some functions as normal callable functions with
  ENTRY/ENDPROC.

- Add an empty unwind hint to return_to_handler().  The return address
  isn't on the stack, so there's nothing ORC can do there.  It will just
  punt in the unlikely case it tries to unwind from that code.

With all that fixed, remove the OBJECT_FILES_NON_STANDARD Makefile
annotation so objtool can read the file.

Link: http://lkml.kernel.org/r/20180123040746.ih4ep3tk4pbjvg7c@treble

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Josh Poimboeuf 2018-01-22 22:07:46 -06:00 committed by Steven Rostedt (VMware)
parent 0c5b9b5d9a
commit e2ac83d74a
2 changed files with 19 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
arch/x86/kernel/Makefile
View File

@ -29,10 +29,13 @@ KASAN_SANITIZE_stacktrace.o := n
KASAN_SANITIZE_paravirt.o := n
OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
OBJECT_FILES_NON_STANDARD_test_nx.o := y
OBJECT_FILES_NON_STANDARD_paravirt_patch_$(BITS).o := y
ifdef CONFIG_FRAME_POINTER
OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o := y
endif
# If instrumentation of this dir is enabled, boot hangs during first second.
# Probably could be more selective here, but note that files related to irqs,
# boot, dumpstack/stacktrace, etc are either non-interesting or can lead to

24
arch/x86/kernel/ftrace_64.S
View File

@ -8,6 +8,7 @@
#include <asm/ftrace.h>
#include <asm/export.h>
#include <asm/nospec-branch.h>
#include <asm/unwind_hints.h>
.code64
.section .entry.text, "ax"
@ -20,7 +21,6 @@ EXPORT_SYMBOL(__fentry__)
EXPORT_SYMBOL(mcount)
#endif
/* All cases save the original rbp (8 bytes) */
#ifdef CONFIG_FRAME_POINTER
# ifdef CC_USING_FENTRY
/* Save parent and function stack frames (rip and rbp) */
@ -31,7 +31,7 @@ EXPORT_SYMBOL(mcount)
# endif
#else
/* No need to save a stack frame */
# define MCOUNT_FRAME_SIZE 8
# define MCOUNT_FRAME_SIZE 0
#endif /* CONFIG_FRAME_POINTER */
/* Size of stack used to save mcount regs in save_mcount_regs */
@ -64,10 +64,10 @@ EXPORT_SYMBOL(mcount)
*/
.macro save_mcount_regs added=0
/* Always save the original rbp */
#ifdef CONFIG_FRAME_POINTER
/* Save the original rbp */
pushq %rbp
#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
@ -105,7 +105,11 @@ EXPORT_SYMBOL(mcount)
* Save the original RBP. Even though the mcount ABI does not
* require this, it helps out callers.
*/
#ifdef CONFIG_FRAME_POINTER
movq MCOUNT_REG_SIZE-8(%rsp), %rdx
#else
movq %rbp, %rdx
#endif
movq %rdx, RBP(%rsp)
/* Copy the parent address into %rsi (second parameter) */
@ -148,7 +152,7 @@ EXPORT_SYMBOL(mcount)
ENTRY(function_hook)
retq
END(function_hook)
ENDPROC(function_hook)
ENTRY(ftrace_caller)
/* save_mcount_regs fills in first two parameters */
@ -184,7 +188,7 @@ GLOBAL(ftrace_graph_call)
/* This is weak to keep gas from relaxing the jumps */
WEAK(ftrace_stub)
retq
END(ftrace_caller)
ENDPROC(ftrace_caller)
ENTRY(ftrace_regs_caller)
/* Save the current flags before any operations that can change them */
@ -255,7 +259,7 @@ GLOBAL(ftrace_regs_caller_end)
jmp ftrace_epilogue
END(ftrace_regs_caller)
ENDPROC(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
@ -313,9 +317,10 @@ ENTRY(ftrace_graph_caller)
restore_mcount_regs
retq
END(ftrace_graph_caller)
ENDPROC(ftrace_graph_caller)
GLOBAL(return_to_handler)
ENTRY(return_to_handler)
UNWIND_HINT_EMPTY
subq $24, %rsp
/* Save the return values */
@ -330,4 +335,5 @@ GLOBAL(return_to_handler)
movq (%rsp), %rax
addq $24, %rsp
JMP_NOSPEC %rdi
END(return_to_handler)
#endif