linux-kernel - [PATCH] objtool: Don't fail on missing symbol table

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Message-Id: <a96c3f76173c7021a2298bd73362313736e674b6.1610663051.git.jpoimboe@redhat.com>
Date:   Thu, 14 Jan 2021 16:24:15 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] objtool: Don't fail on missing symbol table

Thanks to a recent binutils change which doesn't generate unused
symbols, it's now possible for thunk_64.o be completely empty with
CONFIG_PREEMPTION: no text, no data, no symbols.

We could edit the Makefile to only build that file when
CONFIG_PREEMPTION is enabled, but that will likely create confusion
if/when the thunks end up getting used by some other code again.

Just ignore it and move on.

Reported-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/elf.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index be89c741ba9a..2b0f4f52f7b5 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -380,8 +380,11 @@ static int read_symbols(struct elf *elf)
 
 	symtab = find_section_by_name(elf, ".symtab");
 	if (!symtab) {
-		WARN("missing symbol table");
-		return -1;
+		/*
+		 * A missing symbol table is actually possible if it's an empty
+		 * .o file.  This can happen for thunk_64.o.
+		 */
+		return 0;
 	}
 
 	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
-- 
2.29.2