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Message-ID: <ea97fb1b-be81-4a18-b505-cab08617ece8@huaweicloud.com>
Date: Wed, 3 Apr 2024 15:26:03 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: bpf@...r.kernel.org, linux-riscv@...ts.infradead.org,
netdev@...r.kernel.org
Cc: Björn Töpel <bjorn@...nel.org>,
Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
<martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Palmer Dabbelt <palmer@...belt.com>,
Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next v2 1/2] riscv, bpf: Add 12-argument support for
RV64 bpf trampoline
On 2024/4/3 12:17, Pu Lehui wrote:
> From: Pu Lehui <pulehui@...wei.com>
>
> This patch adds 12 function arguments support for riscv64 bpf
> trampoline. The current bpf trampoline supports <= sizeof(u64) bytes
> scalar arguments [0] and <= 16 bytes struct arguments [1]. Therefore, we
> focus on the situation where scalars are at most XLEN bits and
> aggregates whose total size does not exceed 2×XLEN bits in the riscv
> calling convention [2].
>
> Link: https://elixir.bootlin.com/linux/v6.8/source/kernel/bpf/btf.c#L6184 [0]
> Link: https://elixir.bootlin.com/linux/v6.8/source/kernel/bpf/btf.c#L6769 [1]
> Link: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/releases/download/draft-20230929-e5c800e661a53efe3c2678d71a306323b60eb13b/riscv-abi.pdf [2]
> Signed-off-by: Pu Lehui <pulehui@...wei.com>
> Acked-by: Björn Töpel <bjorn@...nel.org>
> Reviewed-by: Björn Töpel <bjorn@...osinc.com>
> ---
> arch/riscv/net/bpf_jit_comp64.c | 65 +++++++++++++++++++++++----------
> 1 file changed, 46 insertions(+), 19 deletions(-)
>
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 77ea306452d4..7e2d6e8c60c2 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -14,6 +14,7 @@
> #include <asm/cfi.h>
> #include "bpf_jit.h"
>
> +#define RV_MAX_ARGS_REG 8
Sorry for the noise. The macro and variable names look really weird. I
will send new patch for the name alignment:
nr_reg_args: number of args in reg
nr_stack_args: number of args on stack
RV_MAX_REG_ARGS: macro for riscv max args in reg
> #define RV_FENTRY_NINSNS 2
>
> #define RV_REG_TCC RV_REG_A6
> @@ -688,26 +689,44 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> return ret;
> }
>
> -static void store_args(int nregs, int args_off, struct rv_jit_context *ctx)
> +static void store_args(int nr_arg_slots, int args_off, struct rv_jit_context *ctx)
> {
> int i;
>
> - for (i = 0; i < nregs; i++) {
> - emit_sd(RV_REG_FP, -args_off, RV_REG_A0 + i, ctx);
> + for (i = 0; i < nr_arg_slots; i++) {
> + if (i < RV_MAX_ARGS_REG) {
> + emit_sd(RV_REG_FP, -args_off, RV_REG_A0 + i, ctx);
> + } else {
> + /* skip slots for T0 and FP of traced function */
> + emit_ld(RV_REG_T1, 16 + (i - RV_MAX_ARGS_REG) * 8, RV_REG_FP, ctx);
> + emit_sd(RV_REG_FP, -args_off, RV_REG_T1, ctx);
> + }
> args_off -= 8;
> }
> }
>
> -static void restore_args(int nregs, int args_off, struct rv_jit_context *ctx)
> +static void restore_args(int nr_args_reg, int args_off, struct rv_jit_context *ctx)
> {
> int i;
>
> - for (i = 0; i < nregs; i++) {
> + for (i = 0; i < nr_args_reg; i++) {
> emit_ld(RV_REG_A0 + i, -args_off, RV_REG_FP, ctx);
> args_off -= 8;
> }
> }
>
> +static void restore_stack_args(int nr_args_stack, int args_off, int stk_arg_off, struct rv_jit_context *ctx)
> +{
> + int i;
> +
> + for (i = 0; i < nr_args_stack; i++) {
> + emit_ld(RV_REG_T1, -(args_off - RV_MAX_ARGS_REG * 8), RV_REG_FP, ctx);
> + emit_sd(RV_REG_FP, -stk_arg_off, RV_REG_T1, ctx);
> + args_off -= 8;
> + stk_arg_off -= 8;
> + }
> +}
> +
> static int invoke_bpf_prog(struct bpf_tramp_link *l, int args_off, int retval_off,
> int run_ctx_off, bool save_ret, struct rv_jit_context *ctx)
> {
> @@ -780,8 +799,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> {
> int i, ret, offset;
> int *branches_off = NULL;
> - int stack_size = 0, nregs = m->nr_args;
> - int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off;
> + int stack_size = 0, nr_arg_slots = 0;
> + int retval_off, args_off, nregs_off, ip_off, run_ctx_off, sreg_off, stk_arg_off;
> struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
> struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
> struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
> @@ -827,20 +846,21 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> * FP - sreg_off [ callee saved reg ]
> *
> * [ pads ] pads for 16 bytes alignment
> + *
> + * [ stack_argN ]
> + * [ ... ]
> + * FP - stk_arg_off [ stack_arg1 ] BPF_TRAMP_F_CALL_ORIG
> */
>
> if (flags & (BPF_TRAMP_F_ORIG_STACK | BPF_TRAMP_F_SHARE_IPMODIFY))
> return -ENOTSUPP;
>
> - /* extra regiters for struct arguments */
> - for (i = 0; i < m->nr_args; i++)
> - if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG)
> - nregs += round_up(m->arg_size[i], 8) / 8 - 1;
> -
> - /* 8 arguments passed by registers */
> - if (nregs > 8)
> + if (m->nr_args > MAX_BPF_FUNC_ARGS)
> return -ENOTSUPP;
>
> + for (i = 0; i < m->nr_args; i++)
> + nr_arg_slots += round_up(m->arg_size[i], 8) / 8;
> +
> /* room of trampoline frame to store return address and frame pointer */
> stack_size += 16;
>
> @@ -850,7 +870,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> retval_off = stack_size;
> }
>
> - stack_size += nregs * 8;
> + stack_size += nr_arg_slots * 8;
> args_off = stack_size;
>
> stack_size += 8;
> @@ -867,8 +887,14 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> stack_size += 8;
> sreg_off = stack_size;
>
> + if (nr_arg_slots - RV_MAX_ARGS_REG > 0)
> + stack_size += (nr_arg_slots - RV_MAX_ARGS_REG) * 8;
> +
> stack_size = round_up(stack_size, 16);
>
> + /* room for args on stack must be at the top of stack*/
> + stk_arg_off = stack_size;
> +
> if (!is_struct_ops) {
> /* For the trampoline called from function entry,
> * the frame of traced function and the frame of
> @@ -904,10 +930,10 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> emit_sd(RV_REG_FP, -ip_off, RV_REG_T1, ctx);
> }
>
> - emit_li(RV_REG_T1, nregs, ctx);
> + emit_li(RV_REG_T1, nr_arg_slots, ctx);
> emit_sd(RV_REG_FP, -nregs_off, RV_REG_T1, ctx);
>
> - store_args(nregs, args_off, ctx);
> + store_args(nr_arg_slots, args_off, ctx);
>
> /* skip to actual body of traced function */
> if (flags & BPF_TRAMP_F_SKIP_FRAME)
> @@ -947,7 +973,8 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> }
>
> if (flags & BPF_TRAMP_F_CALL_ORIG) {
> - restore_args(nregs, args_off, ctx);
> + restore_args(min_t(int, nr_arg_slots, RV_MAX_ARGS_REG), args_off, ctx);
> + restore_stack_args(nr_arg_slots - RV_MAX_ARGS_REG, args_off, stk_arg_off, ctx);
> ret = emit_call((const u64)orig_call, true, ctx);
> if (ret)
> goto out;
> @@ -982,7 +1009,7 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
> }
>
> if (flags & BPF_TRAMP_F_RESTORE_REGS)
> - restore_args(nregs, args_off, ctx);
> + restore_args(min_t(int, nr_arg_slots, RV_MAX_ARGS_REG), args_off, ctx);
>
> if (save_ret) {
> emit_ld(RV_REG_A0, -retval_off, RV_REG_FP, ctx);
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