Objtool currently ignores ___bpf_prog_run() because it doesn't
understand the jump table. This results in the ORC unwinder not being
able to unwind through non-JIT BPF code.
Luckily, the BPF jump table resembles a GCC switch jump table, which
objtool already knows how to read.
Add generic support for reading any static local jump table array named
"jump_table", and rename the BPF variable accordingly, so objtool can
generate ORC data for ___bpf_prog_run().
Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
Reported-by: Song Liu <songliubraving@xxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
kernel/bpf/core.c | 5 ++---
tools/objtool/check.c | 16 ++++++++++++++--
2 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 7c473f208a10..aa546ef7dbdc 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1299,7 +1299,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
{
#define BPF_INSN_2_LBL(x, y) [BPF_##x | BPF_##y] = &&x##_##y
#define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z
- static const void *jumptable[256] = {
+ static const void *jump_table[256] = {
[0 ... 255] = &&default_label,
/* Now overwrite non-defaults ... */
BPF_INSN_MAP(BPF_INSN_2_LBL, BPF_INSN_3_LBL),
@@ -1315,7 +1315,7 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
#define CONT_JMP ({ insn++; goto select_insn; })
select_insn:
- goto *jumptable[insn->code];
+ goto *jump_table[insn->code];
/* ALU */
#define ALU(OPCODE, OP) \
@@ -1558,7 +1558,6 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
BUG_ON(1);
return 0;
}
-STACK_FRAME_NON_STANDARD(___bpf_prog_run); /* jump table */
#define PROG_NAME(stack_size) __bpf_prog_run##stack_size
#define DEFINE_BPF_PROG_RUN(stack_size) \
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 172f99195726..8341c2fff14f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -18,6 +18,8 @@
#define FAKE_JUMP_OFFSET -1
+#define JUMP_TABLE_SYM_PREFIX "jump_table."
+
struct alternative {
struct list_head list;
struct instruction *insn;
@@ -997,6 +999,7 @@ static struct rela *find_switch_table(struct objtool_file *file,
struct instruction *orig_insn = insn;
struct section *rodata_sec;
unsigned long table_offset;
+ struct symbol *sym;
/*
* Backward search using the @first_jump_src links, these help avoid
@@ -1035,9 +1038,18 @@ static struct rela *find_switch_table(struct objtool_file *file,
/*
* Make sure the .rodata address isn't associated with a
- * symbol. gcc jump tables are anonymous data.
+ * symbol. GCC jump tables are anonymous data.
+ *
+ * Also support C jump tables which are in the same format as
+ * switch jump tables. Each jump table should be a static
+ * local const array named "jump_table" for objtool to
+ * recognize it. Note: GCC will add a numbered suffix to the
+ * ELF symbol name, like "jump_table.12345", which it does for
+ * all static local variables.
*/
- if (find_symbol_containing(rodata_sec, table_offset))
+ sym = find_symbol_containing(rodata_sec, table_offset);
+ if (sym && strncmp(sym->name, JUMP_TABLE_SYM_PREFIX,
+ strlen(JUMP_TABLE_SYM_PREFIX)))
continue;
rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
--
2.20.1
