linux-kernel - [PATCH 1/2] objtool/LoongArch: Get table size correctly if LTO is enabled

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Message-ID: <20250812132716.1465-2-yangtiezhu@loongson.cn>
Date: Tue, 12 Aug 2025 21:27:15 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Huacai Chen <chenhuacai@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] objtool/LoongArch: Get table size correctly if LTO is enabled

When compiling with LLVM and CONFIG_LTO_CLANG is set, there exist
many objtool warnings "sibling call from callable instruction with
modified stack frame".

For this special case, the related object file shows that there is
no generated relocation section '.rela.discard.tablejump_annotate'
for the table jump instruction jirl, thus objtool can not know that
what is the actual destination address.

It needs to do something on the LLVM side to make sure that there is
the relocation section '.rela.discard.tablejump_annotate' if LTO is
enabled, but in order to maintain compatibility for the current LLVM
compiler, this can be done in the kernel Makefile for now. Ensure it
is aware of linker with LTO, '--loongarch-annotate-tablejump' needs
to be passed via '-mllvm' to ld.lld.

Before doing the above changes, it should handle the special case of
the relocation section '.rela.discard.tablejump_annotate' to get the
correct table size first, otherwise there are many objtool warnings
and errors if LTO is enabled.

There are many different rodata for each function if LTO is enabled,
it is necessary to enhance get_rodata_table_size_by_table_annotate().

Reported-by: Nathan Chancellor <nathan@...nel.org>
Closes: https://lore.kernel.org/loongarch/20250731175655.GA1455142@ax162/
Fixes: b95f852d3af2 ("objtool/LoongArch: Add support for switch table")
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 tools/objtool/arch/loongarch/special.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/objtool/arch/loongarch/special.c b/tools/objtool/arch/loongarch/special.c
index e39f86d97002..a80b75f7b061 100644
--- a/tools/objtool/arch/loongarch/special.c
+++ b/tools/objtool/arch/loongarch/special.c
@@ -27,6 +27,7 @@ static void get_rodata_table_size_by_table_annotate(struct objtool_file *file,
 	struct table_info *next_table;
 	unsigned long tmp_insn_offset;
 	unsigned long tmp_rodata_offset;
+	bool is_valid_list = false;

 	rsec = find_section_by_name(file->elf, ".rela.discard.tablejump_annotate");
 	if (!rsec)
@@ -35,6 +36,12 @@ static void get_rodata_table_size_by_table_annotate(struct objtool_file *file,
 	INIT_LIST_HEAD(&table_list);

 	for_each_reloc(rsec, reloc) {
+		if (reloc->sym->sec->rodata)
+			continue;
+
+		if (strcmp(insn->sec->name, reloc->sym->sec->name))
+			continue;
+
 		orig_table = malloc(sizeof(struct table_info));
 		if (!orig_table) {
 			WARN("malloc failed");
@@ -49,6 +56,22 @@ static void get_rodata_table_size_by_table_annotate(struct objtool_file *file,

 		if (reloc_idx(reloc) + 1 == sec_num_entries(rsec))
 			break;
+
+		if (strcmp(insn->sec->name, (reloc + 1)->sym->sec->name)) {
+			list_for_each_entry(orig_table, &table_list, jump_info) {
+				if (orig_table->insn_offset == insn->offset) {
+					is_valid_list = true;
+					break;
+				}
+			}
+
+			if (!is_valid_list) {
+				list_del_init(&table_list);
+				continue;
+			}
+
+			break;
+		}
 	}

 	list_for_each_entry(orig_table, &table_list, jump_info) {
-- 
2.42.0