linux-kernel - [PATCH v3 1/8] objtool: Limit unreachable warnings to once per function

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Date:   Tue, 18 Apr 2023 14:27:47 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v3 1/8] objtool: Limit unreachable warnings to once per function

Unreachable instruction warnings are limited to once per object file.
That no longer makes sense for vmlinux validation, which might have
more unreachable instructions lurking in other places.  Change it to
once per function.

Note this affects some other (much rarer) non-fatal warnings as well.
In general I think one-warning-per-function makes sense, as related
warnings can accumulate quickly and we want to eventually get back to
failing the build with -Werror anyway.

Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 tools/objtool/check.c                | 5 +++--
 tools/objtool/include/objtool/elf.h  | 1 +
 tools/objtool/include/objtool/warn.h | 7 ++++++-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 5b600bbf2389..a00931342c7e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4514,6 +4514,7 @@ static int validate_sls(struct objtool_file *file)
 static int validate_reachable_instructions(struct objtool_file *file)
 {
 	struct instruction *insn;
+	int warnings = 0;
 
 	if (file->ignore_unreachables)
 		return 0;
@@ -4523,10 +4524,10 @@ static int validate_reachable_instructions(struct objtool_file *file)
 			continue;
 
 		WARN_INSN(insn, "unreachable instruction");
-		return 1;
+		warnings++;
 	}
 
-	return 0;
+	return warnings;
 }
 
 int check(struct objtool_file *file)
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e1ca588eb69d..78e2d0fc21ca 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -61,6 +61,7 @@ struct symbol {
 	u8 return_thunk      : 1;
 	u8 fentry            : 1;
 	u8 profiling_func    : 1;
+	u8 warned	     : 1;
 	struct list_head pv_target;
 	struct list_head reloc_list;
 };
diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index b1c920dc9516..f195deab456e 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -55,7 +55,12 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 
 #define WARN_INSN(insn, format, ...)					\
 ({									\
-	WARN_FUNC(format, insn->sec, insn->offset,  ##__VA_ARGS__);	\
+	struct instruction *_insn = (insn);				\
+	if (!_insn->sym || !_insn->sym->warned)				\
+		WARN_FUNC(format, _insn->sec, _insn->offset,		\
+			  ##__VA_ARGS__);				\
+	if (_insn->sym)							\
+		_insn->sym->warned = 1;					\
 })
 
 #define BT_FUNC(format, insn, ...)			\
-- 
2.39.2