On 2026/8/14 14:49, Pu Lehui wrote: > > On 2026/8/14 9:29, Feng Jiang wrote: >> Add bpf_jit_supports_stack_args() for the RV64 JIT so BPF subprograms >> and kfuncs can receive more than 5 arguments via the stack >> (BPF_REG_PARAMS / r11). >> >> For BPF-to-BPF calls the caller writes outgoing arguments at the >> bottom of its frame (SP-relative). The callee reads them with >> FP-relative loads. Its FP is set to the caller SP in the prologue, >> so the offsets match. >> >> The RISC-V ABI puts arguments 6-8 in A5-A7 and arguments 9+ at >> SP+0. Before each kfunc call, load arguments 6-8 from the outgoing >> area into A5-A7 and copy any remaining arguments down so argument 9 >> lands at SP+0. >> >> A5 (BPF_REG_0), A6 (TCC) and A7 are safe to clobber here: R0 is not >> live before a call, TCC is backed up on the stack, and A7 is unused >> by the JIT. >> >> Limit the existing kfunc sign-extension loop to MAX_BPF_FUNC_REG_ARGS >> iterations; otherwise idx >= 5 resolves to S1-S5 (BPF_R6-FP) and >> corrupts callee-saved registers. >> >> Signed-off-by: Feng Jiang <[email protected]> >> --- >> arch/riscv/net/bpf_jit.h | 1 + >> arch/riscv/net/bpf_jit_comp64.c | 79 >> +++++++++++++++++++++++++++++++++++++++-- >> arch/riscv/net/bpf_jit_core.c | 4 +++ >> 3 files changed, 81 insertions(+), 3 deletions(-) >> >> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h >> index 419b9d795f2a..9eb4e149505d 100644 >> --- a/arch/riscv/net/bpf_jit.h >> +++ b/arch/riscv/net/bpf_jit.h >> @@ -82,6 +82,7 @@ struct rv_jit_context { >> unsigned long flags; >> int stack_size; >> int tcc_offset; >> + u16 stack_arg_size; >> u64 arena_vm_start; >> u64 user_vm_start; >> }; >> diff --git a/arch/riscv/net/bpf_jit_comp64.c >> b/arch/riscv/net/bpf_jit_comp64.c >> index 6b9972b07c1b..58cb3e5ff6b4 100644 >> --- a/arch/riscv/net/bpf_jit_comp64.c >> +++ b/arch/riscv/net/bpf_jit_comp64.c >> @@ -1815,18 +1815,43 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, >> struct rv_jit_context *ctx, >> if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) { >> const struct btf_func_model *fm; >> - int idx; >> + int idx, nargs; >> fm = bpf_jit_find_kfunc_model(ctx->prog, insn); >> if (!fm) >> return -EINVAL; >> - for (idx = 0; idx < fm->nr_args; idx++) { >> + nargs = min_t(int, fm->nr_args, MAX_BPF_FUNC_REG_ARGS); >> + for (idx = 0; idx < nargs; idx++) { >> u8 reg = bpf_to_rv_reg(BPF_REG_1 + idx, ctx); >> if (fm->arg_size[idx] == sizeof(int)) >> emit_sextw(reg, reg, ctx); >> } >> + >> + /* BPF stack args -> RISC-V ABI: args 6-8 in A5-A7, 9+ at SP+0 >> */ >> + if (fm->nr_args > MAX_BPF_FUNC_REG_ARGS) { >> + int n_stack = fm->nr_args - MAX_BPF_FUNC_REG_ARGS; >> + int n_reg = min_t(int, n_stack, >> + RV_MAX_REG_ARGS - MAX_BPF_FUNC_REG_ARGS); >> + >> + for (idx = 0; idx < n_reg; idx++) { >> + int sz = fm->arg_size[MAX_BPF_FUNC_REG_ARGS + idx]; >> + >> + emit_ld(RV_REG_A5 + idx, idx * 8, RV_REG_SP, ctx); >> + if (sz == sizeof(int)) >> + emit_sextw(RV_REG_A5 + idx, RV_REG_A5 + idx, ctx); > > Hi Feng Jiang, > > Thanks for doing this. I'll squeeze the time to review this patchset, but > there is currently an issue with RV64 kfunc [0]. Let's hold off for a > moment.:) > > [0] > https://lore.kernel.org/bpf/[email protected] >
Thanks for the heads-up. I'll wait for it to land and rebase on top. -- With Best Regards, Feng Jiang
