linux-kernel - [RFC][PATCH 04/16] objtool: Annotate identity

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Date:   Thu, 12 Mar 2020 14:41:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de, jpoimboe@...hat.com
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, peterz@...radead.org
Subject: [RFC][PATCH 04/16] objtool: Annotate identity_mapped()

Normally identity_mapped is not visible to objtool, due to:

  arch/x86/kernel/Makefile:OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o := y

However, when we want to run objtool on vmlinux.o there is no hiding
it. Without the annotation we'll get complaints about the:

	call 1f
1:	popq %rB

construct from the add_call_destinations() pass. Because
identity_mapped() is a SYM_CODE_START_LOCAL_NOALIGN() it is STT_NOTYPE
and we need sym_for_each_insn() to iterate the actual instructions.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/relocate_kernel_64.S |    2 ++
 include/linux/frame.h                |   16 ++++++++++++++++
 tools/objtool/check.c                |    4 ++--
 3 files changed, 20 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -5,6 +5,7 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/frame.h>
 #include <asm/page_types.h>
 #include <asm/kexec.h>
 #include <asm/processor-flags.h>
@@ -210,6 +211,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_ma
 	pushq	%rax
 	ret
 SYM_CODE_END(identity_mapped)
+STACK_FRAME_NON_STANDARD(identity_mapped)
 
 SYM_CODE_START_LOCAL_NOALIGN(virtual_mapped)
 	movq	RSP(%r8), %rsp
--- a/include/linux/frame.h
+++ b/include/linux/frame.h
@@ -3,6 +3,9 @@
 #define _LINUX_FRAME_H
 
 #ifdef CONFIG_STACK_VALIDATION
+
+#ifndef __ASSEMBLY__
+
 /*
  * This macro marks the given function's stack frame as "non-standard", which
  * tells objtool to ignore the function when doing stack metadata validation.
@@ -15,6 +18,19 @@
 	static void __used __section(.discard.func_stack_frame_non_standard) \
 		*__func_stack_frame_non_standard_##func = func
 
+#else /* __ASSEMBLY__ */
+
+#define STACK_FRAME_NON_STANDARD(func) \
+	.pushsection .discard.func_stack_frame_non_standard, "aw"; \
+	.align 8; \
+	.type __func_stack_frame_non_standard_##func, @object; \
+	.size __func_stack_frame_non_standard_##func, 8; \
+__func_stack_frame_non_standard_##func: \
+	.quad func; \
+	.popsection
+
+#endif /* __ASSEMBLY */
+
 #else /* !CONFIG_STACK_VALIDATION */
 
 #define STACK_FRAME_NON_STANDARD(func)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -416,7 +416,7 @@ static void add_ignores(struct objtool_f
 
 		case STT_SECTION:
 			func = find_symbol_by_offset(rela->sym->sec, rela->addend);
-			if (!func || func->type != STT_FUNC)
+			if (!func || (func->type != STT_FUNC && func->type != STT_NOTYPE))
 				continue;
 			break;
 
@@ -425,7 +425,7 @@ static void add_ignores(struct objtool_f
 			continue;
 		}
 
-		func_for_each_insn(file, func, insn)
+		sym_for_each_insn(file, func, insn)
 			insn->ignore = true;
 	}
 }