On Mon, 9 Dec 2019 at 19:52, Paul Chaignon <paul.chaignon@xxxxxxxxxx> wrote:
>
> All BPF JIT compilers except RISC-V's and MIPS' enforce a 33-tail calls
> limit at runtime. In addition, a test was recently added, in tailcalls2,
> to check this limit.
>
> This patch updates the tail call limit in RISC-V's JIT compiler to allow
> 33 tail calls. I tested it using the above selftest on an emulated
> RISCV64.
>
33! ICK! ;-) Thanks for finding this!
Acked-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
> Fixes: 2353ecc6f91f ("bpf, riscv: add BPF JIT for RV64G")
> Reported-by: Mahshid Khezri <khezri.mahshid@xxxxxxxxx>
> Signed-off-by: Paul Chaignon <paul.chaignon@xxxxxxxxxx>
> ---
> arch/riscv/net/bpf_jit_comp.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp.c b/arch/riscv/net/bpf_jit_comp.c
> index 5451ef3845f2..7fbf56aab661 100644
> --- a/arch/riscv/net/bpf_jit_comp.c
> +++ b/arch/riscv/net/bpf_jit_comp.c
> @@ -631,14 +631,14 @@ static int emit_bpf_tail_call(int insn, struct rv_jit_context *ctx)
> return -1;
> emit(rv_bgeu(RV_REG_A2, RV_REG_T1, off >> 1), ctx);
>
> - /* if (--TCC < 0)
> + /* if (TCC-- < 0)
> * goto out;
> */
> emit(rv_addi(RV_REG_T1, tcc, -1), ctx);
> off = (tc_ninsn - (ctx->ninsns - start_insn)) << 2;
> if (is_13b_check(off, insn))
> return -1;
> - emit(rv_blt(RV_REG_T1, RV_REG_ZERO, off >> 1), ctx);
> + emit(rv_blt(tcc, RV_REG_ZERO, off >> 1), ctx);
>
> /* prog = array->ptrs[index];
> * if (!prog)
> --
> 2.17.1
>
