[PATCH v5 5/8] objtool: Check local label about sibling call
From: Tiezhu Yang
Date: Wed Nov 29 2023 - 08:07:29 EST
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+0x1c: 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 6.7.test]$ gcc --version
gcc (GCC) 14.0.0 20231127 (experimental)
[fedora@linux 6.7.test]$ as --version
GNU assembler (GNU Binutils) 2.41.50.20231127
[fedora@linux 6.7.test]$ objdump -M no-aliases -D init/version.o | grep -A 20 "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: 64001480 bge $a0, $zero, 20 # 30 <.L2>
20: 1a000004 pcalau12i $a0, 0
24: 02810005 addi.w $a1, $zero, 64
28: 02c00084 addi.d $a0, $a0, 0
2c: 54000000 bl 0 # 2c <early_hostname+0x2c>
0000000000000030 <.L2>:
30: 28c02061 ld.d $ra, $sp, 8
34: 00150004 or $a0, $zero, $zero
38: 02c04063 addi.d $sp, $sp, 16
3c: 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 e94756e09ca9..29b3c5495901 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 +
@@ -2522,6 +2534,9 @@ 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;
@@ -3690,7 +3705,7 @@ 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;
@@ -3711,7 +3726,7 @@ 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;
@@ -3875,7 +3890,7 @@ 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 9f71e988eca4..2b8a69de4db8 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;
};
--
2.42.0