Commit 7b6c7a87 authored by Josh Poimboeuf's avatar Josh Poimboeuf
Browse files

x86/ftrace: Remove OBJECT_FILES_NON_STANDARD usage 



The file-wide OBJECT_FILES_NON_STANDARD annotation is used with
CONFIG_FRAME_POINTER to tell objtool to skip the entire file when frame
pointers are enabled.  However that annotation is now deprecated because
it doesn't work with IBT, where objtool runs on vmlinux.o instead of
individual translation units.

Instead, use more fine-grained function-specific annotations:

- The 'save_mcount_regs' macro does funny things with the frame pointer.
  Use STACK_FRAME_NON_STANDARD_FP to tell objtool to ignore the
  functions using it.

- The return_to_handler() "function" isn't actually a callable function.
  Instead of being called, it's returned to.  The real return address
  isn't on the stack, so unwinding is already doomed no matter which
  unwinder is used.  So just remove the STT_FUNC annotation, telling
  objtool to ignore it.  That also removes the implicit
  ANNOTATE_NOENDBR, which now needs to be made explicit.

Fixes the following warning:

  vmlinux.o: warning: objtool: __fentry__+0x16: return with modified stack frame

Fixes: ed53a0d9 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
Reported-by: default avatarkernel test robot <lkp@intel.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/b7a7a42fe306aca37826043dac89e113a1acdbac.1654268610.git.jpoimboe@kernel.org
parent dcea997b

arch/x86/kernel/Makefile

+0 −4
Original line number Diff line number Diff line
@@ -36,10 +36,6 @@ KCSAN_SANITIZE := n 


OBJECT_FILES_NON_STANDARD_test_nx.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

arch/x86/kernel/ftrace_64.S

+8 −3
Original line number Diff line number Diff line
@@ -175,6 +175,7 @@ SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL) 


	jmp ftrace_epilogue

SYM_FUNC_END(ftrace_caller);

STACK_FRAME_NON_STANDARD_FP(ftrace_caller)



SYM_FUNC_START(ftrace_epilogue)

/*
@@ -282,6 +283,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL) 
	jmp	ftrace_epilogue



SYM_FUNC_END(ftrace_regs_caller)

STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)





#else /* ! CONFIG_DYNAMIC_FTRACE */
@@ -311,10 +313,14 @@ trace: 
	jmp ftrace_stub

SYM_FUNC_END(__fentry__)

EXPORT_SYMBOL(__fentry__)

STACK_FRAME_NON_STANDARD_FP(__fentry__)



#endif /* CONFIG_DYNAMIC_FTRACE */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

SYM_FUNC_START(return_to_handler)

SYM_CODE_START(return_to_handler)

	UNWIND_HINT_EMPTY

	ANNOTATE_NOENDBR

	subq  $16, %rsp



	/* Save the return values */
@@ -339,7 +345,6 @@ SYM_FUNC_START(return_to_handler) 
	int3

.Ldo_rop:

	mov %rdi, (%rsp)

	UNWIND_HINT_FUNC

	RET

SYM_FUNC_END(return_to_handler)

SYM_CODE_END(return_to_handler)

#endif

include/linux/objtool.h

+6 −0
Original line number Diff line number Diff line
@@ -143,6 +143,12 @@ struct unwind_hint { 
	.popsection

.endm



.macro STACK_FRAME_NON_STANDARD_FP func:req

#ifdef CONFIG_FRAME_POINTER

	STACK_FRAME_NON_STANDARD \func

#endif

.endm



.macro ANNOTATE_NOENDBR

.Lhere_\@:

	.pushsection .discard.noendbr

tools/include/linux/objtool.h

+6 −0
Original line number Diff line number Diff line
@@ -143,6 +143,12 @@ struct unwind_hint { 
	.popsection

.endm



.macro STACK_FRAME_NON_STANDARD_FP func:req

#ifdef CONFIG_FRAME_POINTER

	STACK_FRAME_NON_STANDARD \func

#endif

.endm



.macro ANNOTATE_NOENDBR

.Lhere_\@:

	.pushsection .discard.noendbr