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Message-ID: <426fdad5-17a5-41e7-57b9-aa4c1a4f4327@huaweicloud.com>
Date: Thu, 5 Jan 2023 11:47:27 +0800
From: Pu Lehui <pulehui@...weicloud.com>
To: Yonghong Song <yhs@...a.com>, bpf@...r.kernel.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
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>,
Pu Lehui <pulehui@...wei.com>
Subject: Re: [PATCH bpf-next] bpf, x86: Simplify the parsing logic of
structure parameters
On 2023/1/5 2:24, Yonghong Song wrote:
>
>
> On 1/2/23 5:31 PM, Pu Lehui wrote:
>> From: Pu Lehui <pulehui@...wei.com>
>>
>> Extra_nregs of structure parameters and nr_args can be
>> added directly at the beginning, and using a flip flag
>> to identifiy structure parameters. Meantime, renaming
>> some variables to make them more sense.
>>
>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>
> Thanks for refactoring. Using nr_regs instead of nr_args indeed
> making things easier to understand. Ack with a few nits below.
>
> Acked-by: Yonghong Song <yhs@...com>
>
>> ---
>> arch/x86/net/bpf_jit_comp.c | 99 +++++++++++++++++--------------------
>> 1 file changed, 46 insertions(+), 53 deletions(-)
>>
>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>> index e3e2b57e4e13..e7b72299f5a4 100644
>> --- a/arch/x86/net/bpf_jit_comp.c
>> +++ b/arch/x86/net/bpf_jit_comp.c
>> @@ -1839,62 +1839,57 @@ st: if (is_imm8(insn->off))
>> return proglen;
>> }
>> -static void save_regs(const struct btf_func_model *m, u8 **prog, int
>> nr_args,
>> +static void save_regs(const struct btf_func_model *m, u8 **prog, int
>> nr_regs,
>> int stack_size)
>> {
>> - int i, j, arg_size, nr_regs;
>> + int i, j, arg_size;
>> + bool is_struct = false;
>> +
>> /* Store function arguments to stack.
>> * For a function that accepts two pointers the sequence will be:
>> * mov QWORD PTR [rbp-0x10],rdi
>> * mov QWORD PTR [rbp-0x8],rsi
>> */
>> - for (i = 0, j = 0; i < min(nr_args, 6); i++) {
>> - if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) {
>> - nr_regs = (m->arg_size[i] + 7) / 8;
>> + for (i = 0, j = 0; i < min(nr_regs, 6); i++) {
>> + arg_size = m->arg_size[j];
>> + if (arg_size > 8) {
>> arg_size = 8;
>> - } else {
>> - nr_regs = 1;
>> - arg_size = m->arg_size[i];
>> + is_struct ^= 1;
>> }
>> - while (nr_regs) {
>> - emit_stx(prog, bytes_to_bpf_size(arg_size),
>> - BPF_REG_FP,
>> - j == 5 ? X86_REG_R9 : BPF_REG_1 + j,
>> - -(stack_size - j * 8));
>> - nr_regs--;
>> - j++;
>> - }
>> + emit_stx(prog, bytes_to_bpf_size(arg_size),
>> + BPF_REG_FP,
>> + i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
>> + -(stack_size - i * 8));
>> +
>> + j = is_struct ? j : j + 1;
>> }
>> }
>> -static void restore_regs(const struct btf_func_model *m, u8 **prog,
>> int nr_args,
>> +static void restore_regs(const struct btf_func_model *m, u8 **prog,
>> int nr_regs,
>> int stack_size)
>> {
>> - int i, j, arg_size, nr_regs;
>> + int i, j, arg_size;
>> + bool is_struct = false;
>
> Maybe
> bool next_same_struct = false
> to better characterize what it means?
>
agree, will do as suggested bellow.
>> /* Restore function arguments from stack.
>> * For a function that accepts two pointers the sequence will be:
>> * EMIT4(0x48, 0x8B, 0x7D, 0xF0); mov rdi,QWORD PTR [rbp-0x10]
>> * EMIT4(0x48, 0x8B, 0x75, 0xF8); mov rsi,QWORD PTR [rbp-0x8]
>> */
>> - for (i = 0, j = 0; i < min(nr_args, 6); i++) {
>> - if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) {
>> - nr_regs = (m->arg_size[i] + 7) / 8;
>> + for (i = 0, j = 0; i < min(nr_regs, 6); i++) {
>
> Let us put a comment here so the later users can understand the logic
> behind 'is_struct ^= 1'.
>
> /* The arg_size is at most 16 bytes, enforced by the verifier. */
>
>> + arg_size = m->arg_size[j];
>> + if (arg_size > 8) {
>> arg_size = 8;
>> - } else {
>> - nr_regs = 1;
>> - arg_size = m->arg_size[i];
>> + is_struct ^= 1;
>
> next_same_struct = !next_same_struct;
>
> The same for above save_regs().
>
>> }
>> - while (nr_regs) {
>> - emit_ldx(prog, bytes_to_bpf_size(arg_size),
>> - j == 5 ? X86_REG_R9 : BPF_REG_1 + j,
>> - BPF_REG_FP,
>> - -(stack_size - j * 8));
>> - nr_regs--;
>> - j++;
>> - }
>> + emit_ldx(prog, bytes_to_bpf_size(arg_size),
>> + i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
>> + BPF_REG_FP,
>> + -(stack_size - i * 8));
>> +
>> + j = is_struct ? j : j + 1;
>> }
>> }
> [...]
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