linux-kernel - [PATCH v4 7/8] objtool: Check local label in read_unwind

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Date:   Mon, 23 Oct 2023 16:11:30 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: [PATCH v4 7/8] objtool: Check local label in read_unwind_hints()

When update the latest upstream gcc and binutils which enables linker
relaxation by default, it generates more objtool warnings on LoongArch.

We can see that the reloc sym name is local label instead of section
in relocation section '.rela.discard.unwind_hints', in this case, the
reloc sym type is STT_NOTYPE instead of STT_SECTION. Let us check it
to not return -1, then use reloc->sym->offset instead of reloc addend
which is 0 to find the corresponding instruction.

Here are some detailed info:
[fedora@...ux 6.6.test]$ gcc --version
gcc (GCC) 14.0.0 20231009 (experimental)
[fedora@...ux 6.6.test]$ as --version
GNU assembler (GNU Binutils) 2.41.50.20231009
[fedora@...ux 6.6.test]$ readelf -r arch/loongarch/kernel/entry.o | grep -A 2 "rela.discard.unwind_hints"
Relocation section '.rela.discard.unwind_hints' at offset 0x458 contains 7 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  000800000063 R_LARCH_32_PCREL  000000000000001c .Lhere_1 + 0

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/objtool/check.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8ddf02f..c2ebb96 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2224,6 +2224,7 @@ static int read_unwind_hints(struct objtool_file *file)
 	struct unwind_hint *hint;
 	struct instruction *insn;
 	struct reloc *reloc;
+	unsigned long offset;
 	int i;
 
 	sec = find_section_by_name(file->elf, ".discard.unwind_hints");
@@ -2251,7 +2252,16 @@ static int read_unwind_hints(struct objtool_file *file)
 			return -1;
 		}
 
-		insn = find_insn(file, reloc->sym->sec, reloc_addend(reloc));
+		if (reloc->sym->type == STT_SECTION) {
+			offset = reloc_addend(reloc);
+		} else if (reloc->sym->local_label) {
+			offset = reloc->sym->offset;
+		} else {
+			WARN("unexpected relocation symbol type in %s", sec->rsec->name);
+			return -1;
+		}
+
+		insn = find_insn(file, reloc->sym->sec, offset);
 		if (!insn) {
 			WARN("can't find insn for unwind_hints[%d]", i);
 			return -1;
-- 
2.1.0