[PATCH] x86/ftrace: Fix objtool vmlinux.o __fentry__ warning

[PATCH] x86/ftrace: Fix objtool vmlinux.o __fentry__ warning

[Josh Poimboeuf]

The 'save_mcount_regs' macro does funny things with the frame pointer,
which objtool doesn't approve of.  So OBJECT_FILES_NON_STANDARD is used
with CONFIG_FRAME_POINTER to tell objtool to skip the entire file when
frame pointers are enabled.

However, the file-wide OBJECT_FILES_NON_STANDARD annotation is now
deprecated, because it doesn't work for IBT, where objtool runs on
vmlinux.o.  Use more fine-grained function-specific annotations
instead.

Fixes the following warning:

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

Fixes: ed53a0d97192 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/kernel/Makefile      | 4 ----
 arch/x86/kernel/ftrace_64.S   | 4 ++++
 include/linux/objtool.h       | 6 ++++++
 tools/include/linux/objtool.h | 6 ++++++
 4 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 03364dc40d8d..4c8b6ae802ac 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -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
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 4ec13608d3c6..db7c396064ef 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -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 */
@@ -311,6 +313,8 @@ 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
diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index 6491fa8fba6d..15b940ec1eac 100644
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -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
diff --git a/tools/include/linux/objtool.h b/tools/include/linux/objtool.h
index 6491fa8fba6d..15b940ec1eac 100644
--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@@ -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
-- 
2.34.3

Re: [PATCH] x86/ftrace: Fix objtool vmlinux.o __fentry__ warning

[Josh Poimboeuf]

On Wed, Jun 01, 2022 at 09:30:53AM -0700, Josh Poimboeuf wrote:
> The 'save_mcount_regs' macro does funny things with the frame pointer,
> which objtool doesn't approve of.  So OBJECT_FILES_NON_STANDARD is used
> with CONFIG_FRAME_POINTER to tell objtool to skip the entire file when
> frame pointers are enabled.
> 
> However, the file-wide OBJECT_FILES_NON_STANDARD annotation is now
> deprecated, because it doesn't work for IBT, where objtool runs on
> vmlinux.o.  Use more fine-grained function-specific annotations
> instead.
> 
> Fixes the following warning:
> 
>   vmlinux.o: warning: objtool: __fentry__+0x16: return with modified stack frame
> 
> Fixes: ed53a0d97192 ("x86/alternative: Use .ibt_endbr_seal to seal indirect calls")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

NACK - I just found another robot warning for this one.

-- 
Josh