linux-kernel - [PATCH v2 3/9] objtool: Limit unreachable warnings to once per function

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Message-Id: <81ed0b8e5218ac6ecae49af901bf5e0fb3687cef.1681325924.git.jpoimboe@kernel.org>
Date:   Wed, 12 Apr 2023 12:03:18 -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>
Subject: [PATCH v2 3/9] 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 | 5 ++++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e85440db7a5f..de0d0234527d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4509,6 +4509,7 @@ 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;
@@ -4518,10 +4519,10 @@ 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 ad0024da262b..a668173a5869 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..4ef9b278e5fd 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -55,7 +55,10 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 
 #define WARN_INSN(insn, format, ...)					\
 ({									\
-	WARN_FUNC(format, insn->sec, insn->offset,  ##__VA_ARGS__);	\
+	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