linux-kernel - [PATCH v3 6/8] objtool: Check local label in add_dead

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Date:   Fri, 20 Oct 2023 10:26:59 +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 v3 6/8] objtool: Check local label in add_dead_ends()

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

  init/main.o: warning: objtool: unexpected relocation symbol type in .rela.discard.unreachable

We can see that the reloc sym name is local label instead of section
in relocation section '.rela.discard.unreachable', 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. At the same time,
replace the variable "addend" with "offset" to reflect the reality.

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 init/main.o | grep -A 2 "rela.discard.unreachable"
Relocation section '.rela.discard.unreachable' at offset 0x4b70 contains 1 entry:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  00de00000063 R_LARCH_32_PCREL  0000000000000228 .L466^B1 + 0

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/objtool/check.c | 36 +++++++++++++++++++++---------------
 1 file changed, 21 insertions(+), 15 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index a9cb224..eee5621 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -611,7 +611,7 @@ static int add_dead_ends(struct objtool_file *file)
 	struct section *rsec;
 	struct reloc *reloc;
 	struct instruction *insn;
-	s64 addend;
+	unsigned long offset;
 
 	/*
 	 * Check for manually annotated dead ends.
@@ -622,26 +622,29 @@ static int add_dead_ends(struct objtool_file *file)
 
 	for_each_reloc(rsec, reloc) {
 
-		if (reloc->sym->type != STT_SECTION) {
+		if (reloc->sym->type == STT_SECTION) {
+			offset = reloc_addend(reloc);
+		} else if ((reloc->sym->type == STT_NOTYPE) &&
+			    strncmp(reloc->sym->name, ".L", 2) == 0) {
+			offset = reloc->sym->offset;
+		} else {
 			WARN("unexpected relocation symbol type in %s", rsec->name);
 			return -1;
 		}
 
-		addend = reloc_addend(reloc);
-
-		insn = find_insn(file, reloc->sym->sec, addend);
+		insn = find_insn(file, reloc->sym->sec, offset);
 		if (insn)
 			insn = prev_insn_same_sec(file, insn);
-		else if (addend == reloc->sym->sec->sh.sh_size) {
+		else if (offset == reloc->sym->sec->sh.sh_size) {
 			insn = find_last_insn(file, reloc->sym->sec);
 			if (!insn) {
 				WARN("can't find unreachable insn at %s+0x%" PRIx64,
-				     reloc->sym->sec->name, addend);
+				     reloc->sym->sec->name, offset);
 				return -1;
 			}
 		} else {
 			WARN("can't find unreachable insn at %s+0x%" PRIx64,
-			     reloc->sym->sec->name, addend);
+			     reloc->sym->sec->name, offset);
 			return -1;
 		}
 
@@ -661,26 +664,29 @@ static int add_dead_ends(struct objtool_file *file)
 
 	for_each_reloc(rsec, reloc) {
 
-		if (reloc->sym->type != STT_SECTION) {
+		if (reloc->sym->type == STT_SECTION) {
+			offset = reloc_addend(reloc);
+		} else if ((reloc->sym->type == STT_NOTYPE) &&
+			    strncmp(reloc->sym->name, ".L", 2) == 0) {
+			offset = reloc->sym->offset;
+		} else {
 			WARN("unexpected relocation symbol type in %s", rsec->name);
 			return -1;
 		}
 
-		addend = reloc_addend(reloc);
-
-		insn = find_insn(file, reloc->sym->sec, addend);
+		insn = find_insn(file, reloc->sym->sec, offset);
 		if (insn)
 			insn = prev_insn_same_sec(file, insn);
-		else if (addend == reloc->sym->sec->sh.sh_size) {
+		else if (offset == reloc->sym->sec->sh.sh_size) {
 			insn = find_last_insn(file, reloc->sym->sec);
 			if (!insn) {
 				WARN("can't find reachable insn at %s+0x%" PRIx64,
-				     reloc->sym->sec->name, addend);
+				     reloc->sym->sec->name, offset);
 				return -1;
 			}
 		} else {
 			WARN("can't find reachable insn at %s+0x%" PRIx64,
-			     reloc->sym->sec->name, addend);
+			     reloc->sym->sec->name, offset);
 			return -1;
 		}
 
-- 
2.1.0