On Fri, Jun 14, 2019 at 12:56:41PM -0500, Josh Poimboeuf wrote:
> 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>
> Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> 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."
since external tool will be looking at it should it be named
"bpf_jump_table." to avoid potential name conflicts?
Or even more unique name?
Like "bpf_interpreter_jump_table." ?
