[PATCH v4 5/8] objtool: Check local label about sibling call

[Tiezhu Yang]

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

  init/version.o: warning: objtool: early_hostname+0x20: sibling call from callable instruction with modified stack frame

We can see that the branch and jump operation about local label ".L2"
is not sibling call, because a sibling call is a tail-call to another
symbol. In this case, make is_sibling_call() return false, set dest_sec
and dest_off to calculate jump_dest in add_jump_destinations().

As suggested by Peter Zijlstra, add "local_label" member in struct
symbol, then set it as true if symbol type is STT_NOTYPE and symbol
name starts with ".L" string in classify_symbols().

Here are some detailed info:
[fedora@linux 6.6.test]$ gcc --version
gcc (GCC) 14.0.0 20231009 (experimental)
[fedora@linux 6.6.test]$ as --version
GNU assembler (GNU Binutils) 2.41.50.20231009
[fedora@linux 6.6.test]$ objdump -M no-aliases -D init/version.o | grep -A 21 "init.text"
Disassembly of section .init.text:

0000000000000000 <early_hostname>:
   0:	1a00000c 	pcalau12i   	$t0, 0
   4:	02ffc063 	addi.d      	$sp, $sp, -16
   8:	00150085 	or          	$a1, $a0, $zero
   c:	02810406 	addi.w      	$a2, $zero, 65
  10:	02c00184 	addi.d      	$a0, $t0, 0
  14:	29c02061 	st.d        	$ra, $sp, 8
  18:	54000000 	bl          	0	# 18 <early_hostname+0x18>
  1c:	0281000c 	addi.w      	$t0, $zero, 64
  20:	6c001584 	bgeu        	$t0, $a0, 20	# 34 <.L2>
  24:	1a000004 	pcalau12i   	$a0, 0
  28:	02810005 	addi.w      	$a1, $zero, 64
  2c:	02c00084 	addi.d      	$a0, $a0, 0
  30:	54000000 	bl          	0	# 30 <early_hostname+0x30>

0000000000000034 <.L2>:
  34:	28c02061 	ld.d        	$ra, $sp, 8
  38:	00150004 	or          	$a0, $zero, $zero
  3c:	02c04063 	addi.d      	$sp, $sp, 16
  40:	4c000020 	jirl        	$zero, $ra, 0

By the way, it need to move insn_reloc() before is_sibling_call()
to avoid implicit declaration build error.

Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
Reviewed-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
 tools/objtool/check.c               | 71 ++++++++++++++++++++++---------------
 tools/objtool/include/objtool/elf.h |  1 +
 2 files changed, 44 insertions(+), 28 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e308d1b..1b40639 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -20,6 +20,7 @@
 #include <linux/hashtable.h>
 #include <linux/kernel.h>
 #include <linux/static_call_types.h>
+#include <linux/string.h>
 
 struct alternative {
 	struct alternative *next;
@@ -161,12 +162,38 @@ static bool is_jump_table_jump(struct instruction *insn)
 	       insn_jump_table(alt_group->orig_group->first_insn);
 }
 
-static bool is_sibling_call(struct instruction *insn)
+static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
+{
+	struct reloc *reloc;
+
+	if (insn->no_reloc)
+		return NULL;
+
+	if (!file)
+		return NULL;
+
+	reloc = find_reloc_by_dest_range(file->elf, insn->sec,
+					 insn->offset, insn->len);
+	if (!reloc) {
+		insn->no_reloc = 1;
+		return NULL;
+	}
+
+	return reloc;
+}
+
+static bool is_sibling_call(struct objtool_file *file, struct instruction *insn)
 {
 	/*
 	 * Assume only STT_FUNC calls have jump-tables.
 	 */
 	if (insn_func(insn)) {
+		struct reloc *reloc = insn_reloc(file, insn);
+
+		/* Disallow sibling calls into STT_NOTYPE if it is local lable */
+		if (reloc && reloc->sym->local_label)
+			return false;
+
 		/* An indirect jump is either a sibling call or a jump to a table. */
 		if (insn->type == INSN_JUMP_DYNAMIC)
 			return !is_jump_table_jump(insn);
@@ -232,7 +259,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 	 * of the sibling call returns.
 	 */
 	func_for_each_insn(file, func, insn) {
-		if (is_sibling_call(insn)) {
+		if (is_sibling_call(file, insn)) {
 			struct instruction *dest = insn->jump_dest;
 
 			if (!dest)
@@ -743,7 +770,7 @@ static int create_static_call_sections(struct objtool_file *file)
 		if (!elf_init_reloc_data_sym(file->elf, sec,
 					     idx * sizeof(*site) + 4,
 					     (idx * 2) + 1, key_sym,
-					     is_sibling_call(insn) * STATIC_CALL_SITE_TAIL))
+					     is_sibling_call(file, insn) * STATIC_CALL_SITE_TAIL))
 			return -1;
 
 		idx++;
@@ -1315,26 +1342,6 @@ __weak bool arch_is_embedded_insn(struct symbol *sym)
 	return false;
 }
 
-static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
-{
-	struct reloc *reloc;
-
-	if (insn->no_reloc)
-		return NULL;
-
-	if (!file)
-		return NULL;
-
-	reloc = find_reloc_by_dest_range(file->elf, insn->sec,
-					 insn->offset, insn->len);
-	if (!reloc) {
-		insn->no_reloc = 1;
-		return NULL;
-	}
-
-	return reloc;
-}
-
 static void remove_insn_ops(struct instruction *insn)
 {
 	struct stack_op *op, *next;
@@ -1577,8 +1584,13 @@ static int add_jump_destinations(struct objtool_file *file)
 			 * External sibling call or internal sibling call with
 			 * STT_FUNC reloc.
 			 */
-			add_call_dest(file, insn, reloc->sym, true);
-			continue;
+			if (reloc->sym->local_label) {
+				dest_sec = insn->sec;
+				dest_off = arch_jump_destination(insn);
+			} else {
+				add_call_dest(file, insn, reloc->sym, true);
+				continue;
+			}
 		} else if (reloc->sym->sec->idx) {
 			dest_sec = reloc->sym->sec;
 			dest_off = reloc->sym->sym.st_value +
@@ -2506,6 +2518,9 @@ static int classify_symbols(struct objtool_file *file)
 	struct symbol *func;
 
 	for_each_sym(file, func) {
+		if (func->type == STT_NOTYPE && strstarts(func->name, ".L"))
+			func->local_label = true;
+
 		if (func->bind != STB_GLOBAL)
 			continue;
 
@@ -3674,7 +3689,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 		case INSN_JUMP_CONDITIONAL:
 		case INSN_JUMP_UNCONDITIONAL:
-			if (is_sibling_call(insn)) {
+			if (is_sibling_call(file, insn)) {
 				ret = validate_sibling_call(file, insn, &state);
 				if (ret)
 					return ret;
@@ -3695,7 +3710,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
 
 		case INSN_JUMP_DYNAMIC:
 		case INSN_JUMP_DYNAMIC_CONDITIONAL:
-			if (is_sibling_call(insn)) {
+			if (is_sibling_call(file, insn)) {
 				ret = validate_sibling_call(file, insn, &state);
 				if (ret)
 					return ret;
@@ -3859,7 +3874,7 @@ static int validate_unret(struct objtool_file *file, struct instruction *insn)
 
 		case INSN_JUMP_UNCONDITIONAL:
 		case INSN_JUMP_CONDITIONAL:
-			if (!is_sibling_call(insn)) {
+			if (!is_sibling_call(file, insn)) {
 				if (!insn->jump_dest) {
 					WARN_INSN(insn, "unresolved jump target after linking?!?");
 					return -1;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 9f71e98..2b8a69d 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -67,6 +67,7 @@ struct symbol {
 	u8 profiling_func    : 1;
 	u8 warned	     : 1;
 	u8 embedded_insn     : 1;
+	u8 local_label       : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 };
-- 
2.1.0