Re: [PATCH v5 7/9] riscv/kprobe: Prepare detour buffer for optimized kprobe

liaochang (A)
2023-01-04T08:38:25Z

在 2023/1/3 2:04, Björn Töpel 写道:
> Chen Guokai <chenguokai17@mails.ucas.ac.cn> writes:
>
>> From: Liao Chang <liaochang1@huawei.com>
>
>> diff --git a/arch/riscv/kernel/probes/opt.c b/arch/riscv/kernel/probes/opt.c
>> index 258a283c906d..bc232fce5b39 100644
>> --- a/arch/riscv/kernel/probes/opt.c
>> +++ b/arch/riscv/kernel/probes/opt.c
>> @@ -11,9 +11,37 @@
>> #include <linux/kprobes.h>
>> #include <asm/kprobes.h>
>> #include <asm/patch.h>
>> +#include <asm/asm-offsets.h>
>>
>> #include "simulate-insn.h"
>> #include "decode-insn.h"
>> +#include "../../net/bpf_jit.h"
>> +
>> +static void
>
> Super-nit, but I really prefer *not* breaking function name and return
> value, for grepability.

OK, i will keep function name and return at the same line.

>
>> diff --git a/arch/riscv/kernel/probes/opt_trampoline.S b/arch/riscv/kernel/probes/opt_trampoline.S
>> index 16160c4367ff..75e34e373cf2 100644
>> --- a/arch/riscv/kernel/probes/opt_trampoline.S
>> +++ b/arch/riscv/kernel/probes/opt_trampoline.S
>> @@ -1,12 +1,137 @@
>> /* SPDX-License-Identifier: GPL-2.0-only */
>> /*
>> * Copyright (C) 2022 Guokai Chen
>> + * Copyright (C) 2022 Liao, Chang <liaochang1@huawei.com>
>> */
>>
>> #include <linux/linkage.h>
>>
>> +#include <asm/asm.h>
>> #incldue <asm/csr.h>
>> #include <asm/asm-offsets.h>
>>
>> SYM_ENTRY(optprobe_template_entry, SYM_L_GLOBAL, SYM_A_NONE)
>> + addi sp, sp, -(PT_SIZE_ON_STACK)
>> + REG_S x1, PT_RA(sp)
>> + REG_S x2, PT_SP(sp)
>> + REG_S x3, PT_GP(sp)
>> + REG_S x4, PT_TP(sp)
>> + REG_S x5, PT_T0(sp)
>> + REG_S x6, PT_T1(sp)
>> + REG_S x7, PT_T2(sp)
>> + REG_S x8, PT_S0(sp)
>> + REG_S x9, PT_S1(sp)
>> + REG_S x10, PT_A0(sp)
>> + REG_S x11, PT_A1(sp)
>> + REG_S x12, PT_A2(sp)
>> + REG_S x13, PT_A3(sp)
>> + REG_S x14, PT_A4(sp)
>> + REG_S x15, PT_A5(sp)
>> + REG_S x16, PT_A6(sp)
>> + REG_S x17, PT_A7(sp)
>> + REG_S x18, PT_S2(sp)
>> + REG_S x19, PT_S3(sp)
>> + REG_S x20, PT_S4(sp)
>> + REG_S x21, PT_S5(sp)
>> + REG_S x22, PT_S6(sp)
>> + REG_S x23, PT_S7(sp)
>> + REG_S x24, PT_S8(sp)
>> + REG_S x25, PT_S9(sp)
>> + REG_S x26, PT_S10(sp)
>> + REG_S x27, PT_S11(sp)
>> + REG_S x28, PT_T3(sp)
>> + REG_S x29, PT_T4(sp)
>> + REG_S x30, PT_T5(sp)
>> + REG_S x31, PT_T6(sp)
>> + /* Update fp is friendly for stacktrace */
>> + addi s0, sp, (PT_SIZE_ON_STACK)
>> + j 1f
>> +
>> +SYM_ENTRY(optprobe_template_save, SYM_L_GLOBAL, SYM_A_NONE)
>> + /*
>> + * Step1:
>> + * Filled with the pointer to optimized_kprobe data
>> + */
>> + .dword 0
>> +1:
>> + /* Load optimize_kprobe pointer from .dword below */
>> + auipc a0, 0
>> + REG_L a0, -8(a0)
>> + add a1, sp, x0
>> +
>> +SYM_ENTRY(optprobe_template_call, SYM_L_GLOBAL, SYM_A_NONE)
>> + /*
>> + * Step2:
>> + * <IMME> of AUIPC/JALR are modified to the offset to optimized_callback
>> + * jump target is loaded from above .dword.
>> + */
>> + auipc ra, 0
>> + jalr ra, 0(ra)
>> +
>> + REG_L x1, PT_RA(sp)
>> + REG_L x3, PT_GP(sp)
>> + REG_L x4, PT_TP(sp)
>> + REG_L x5, PT_T0(sp)
>> + REG_L x6, PT_T1(sp)
>> + REG_L x7, PT_T2(sp)
>> + REG_L x8, PT_S0(sp)
>> + REG_L x9, PT_S1(sp)
>> + REG_L x10, PT_A0(sp)
>> + REG_L x11, PT_A1(sp)
>> + REG_L x12, PT_A2(sp)
>> + REG_L x13, PT_A3(sp)
>> + REG_L x14, PT_A4(sp)
>> + REG_L x15, PT_A5(sp)
>> + REG_L x16, PT_A6(sp)
>> + REG_L x17, PT_A7(sp)
>> + REG_L x18, PT_S2(sp)
>> + REG_L x19, PT_S3(sp)
>> + REG_L x20, PT_S4(sp)
>> + REG_L x21, PT_S5(sp)
>> + REG_L x22, PT_S6(sp)
>> + REG_L x23, PT_S7(sp)
>> + REG_L x24, PT_S8(sp)
>> + REG_L x25, PT_S9(sp)
>> + REG_L x26, PT_S10(sp)
>> + REG_L x27, PT_S11(sp)
>> + REG_L x28, PT_T3(sp)
>> + REG_L x29, PT_T4(sp)
>> + REG_L x30, PT_T5(sp)
>> + REG_L x31, PT_T6(sp)
>> + REG_L x2, PT_SP(sp)
>> + addi sp, sp, (PT_SIZE_ON_STACK)
>> +
>> +SYM_ENTRY(optprobe_template_insn, SYM_L_GLOBAL, SYM_A_NONE)
>> + /*
>> + * Step3:
>> + * NOPS will be replaced by the probed instruction, at worst case 3 RVC
>> + * and 1 RVI instructions is about to execute out of line.
>> + */
>> + nop
>
> A nop here will be either a compressed nop or a non-compressed,
> depending on the build (C-enabled or not), right? Maybe be explicit to
> the assembler what you want?
>

You are right, if CONFIG_RISCV_ISA_C is disabled, two NOP is enough for 2 RVI execute out of line,
if CONFIG_RISCV_ISA_C is enabled, it needs eight C.NOP here for the worst case (3 RVC + 1 RVI).

I will use {C}.NOP explicitly for different configure in next revision, thanks.

>
> Björn

--
BR,
Liao, Chang