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Subjectping//Re: [PATCH -next 2/2] riscv: implemented branch simulate instructions
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在 2021/6/29 10:34, Chen Lifu 写道:
> To test the kprobe-based event tracing, we prepare
> a kernel module 'kprobe_test.ko' to add the probes.
> The assembly codes (partially) of the module are as follows:
> ...
> 0000000000000000 <kprobe_test_branch>:
> ...
>
> 0000000000000080 <.L7>:
> 80: 414986bb subw a3,s3,s4
> 84: 4785 li a5,1
> 86: 00d7c363 blt a5,a3,8c <.L8>
> 8a: 2485 addiw s1,s1,1
>
> 000000000000008c <.L8>:
> 8c: 012987bb addw a5,s3,s2
> 90: 4711 li a4,4
> 92: 00f75363 bge a4,a5,98 <.L9>
> 96: 2485 addiw s1,s1,1
> ...
>
> 00000000000000aa <.L11>:
> aa: 01299363 bne s3,s2,b0 <.L12>
> ae: 2485 addiw s1,s1,1
>
> 00000000000000b0 <.L12>:
> b0: 012a0363 beq s4,s2,b6 <.L13>
> b4: 2485 addiw s1,s1,1
> ...
>
> 00000000000000c2 <.L14>:
> c2: 0009861b sext.w a2,s3
> c6: 013a7363 bgeu s4,s3,cc <.L15>
> ca: 2485 addiw s1,s1,1
> ...
>
> 00000000000000d2 <.L16>:
> d2: 00e7e363 bltu a5,a4,d8 <.L17>
> d6: 2485 addiw s1,s1,1
> ...
>
> Test the kprobe-based event tracing in qemu-system-riscv64:
> First, install the kprobe test module:
> insmod /root/kprobe_test.ko
>
> Then, add probes as new events at the branch instructions,
> i.e. blt, bge, bne, beq, bgeu and bltu.
> The following errors occur due to the instructions not allowed to probe yet:
> echo "p:blt kprobe_test:kprobe_test_branch+0x86 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
> echo "p:bge kprobe_test:kprobe_test_branch+0x92 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
> echo "p:bne kprobe_test:kprobe_test_branch+0xaa epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
> echo "p:beq kprobe_test:kprobe_test_branch+0xb0 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
> echo "p:bgeu kprobe_test:kprobe_test_branch+0xc6 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
> echo "p:bltu kprobe_test:kprobe_test_branch+0xd2 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> sh: write error: Invalid argument
>
> This patch implemented the branch simulate instructions and allowed to probe them.
> Merge this patch and perform the test again, the test results are as follows:
> First, add probes at the branch instructions:
> echo "p:blt kprobe_test:kprobe_test_branch+0x86 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo "p:bge kprobe_test:kprobe_test_branch+0x92 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo "p:bne kprobe_test:kprobe_test_branch+0xaa epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo "p:beq kprobe_test:kprobe_test_branch+0xb0 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo "p:bgeu kprobe_test:kprobe_test_branch+0xc6 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo "p:bltu kprobe_test:kprobe_test_branch+0xd2 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/blt/enable
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/bge/enable
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/bne/enable
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/beq/enable
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/bgeu/enable
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/bltu/enable
>
> Then, do something to run to the probes.
> After that, see the traced information:
> cat /sys/kernel/debug/tracing/trace
> sysctl-63 [001] d... 2505.263969: blt: (kprobe_test_branch+0x86/0x10e [kprobe_test]) epc=0xffffffff016122f8 opcode=0x100073
> sysctl-63 [001] d... 2505.263991: bge: (kprobe_test_branch+0x92/0x10e [kprobe_test]) epc=0xffffffff01612304 opcode=0x100073
> sysctl-63 [001] d... 2505.264001: bne: (kprobe_test_branch+0xaa/0x10e [kprobe_test]) epc=0xffffffff0161231c opcode=0x100073
> sysctl-63 [001] d... 2505.264011: beq: (kprobe_test_branch+0xb0/0x10e [kprobe_test]) epc=0xffffffff01612322 opcode=0x100073
> sysctl-63 [001] d... 2505.264019: bgeu: (kprobe_test_branch+0xc6/0x10e [kprobe_test]) epc=0xffffffff01612338 opcode=0x100073
> sysctl-63 [001] d... 2505.264027: bltu: (kprobe_test_branch+0xd2/0x10e [kprobe_test]) epc=0xffffffff01612344 opcode=0x100073
>
> Now we can see the traced information.
> The actual address of the symbol 'kprobe_test_branch' is as follows:
> cat /proc/kallsyms | grep kprobe_test_branch
> ffffffff01612272 t kprobe_test_branch [kprobe_test]
>
> Based on the traced information and the actual address of the symbol
> 'kprobe_test_branch', we can also see that the branch instructions
> have been replaced by 'ebreak(0x100073)' instructions.
>
> The pesudoinstructions of the branch instructions,
> i.e. bnez, beqz, blez, bgez, bltz, bgtz, bleu, bgtu and ble
> are allowed to probe as well.
>
> --------
>
> Signed-off-by: Chen Lifu <chenlifu@huawei.com>
> ---
> arch/riscv/kernel/probes/decode-insn.c | 3 +-
> arch/riscv/kernel/probes/simulate-insn.c | 78 ++++++++++++++++++++++++
> 2 files changed, 79 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
> index 5eb03fb61450..64f6183b4717 100644
> --- a/arch/riscv/kernel/probes/decode-insn.c
> +++ b/arch/riscv/kernel/probes/decode-insn.c
> @@ -38,11 +38,10 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
> RISCV_INSN_REJECTED(c_ebreak, insn);
> #endif
>
> - RISCV_INSN_REJECTED(branch, insn);
> -
> RISCV_INSN_SET_SIMULATE(jal, insn);
> RISCV_INSN_SET_SIMULATE(jalr, insn);
> RISCV_INSN_SET_SIMULATE(auipc, insn);
> + RISCV_INSN_SET_SIMULATE(branch, insn);
>
> return INSN_GOOD;
> }
> diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
> index b81719522d5c..efc989b28859 100644
> --- a/arch/riscv/kernel/probes/simulate-insn.c
> +++ b/arch/riscv/kernel/probes/simulate-insn.c
> @@ -117,3 +117,81 @@ bool __kprobes simulate_auipc(u32 opcode, unsigned long addr, struct pt_regs *re
>
> return true;
> }
> +
> +#define branch_rs1_idx(opcode) \
> + (((opcode) >> 15) & 0x1f)
> +
> +#define branch_rs2_idx(opcode) \
> + (((opcode) >> 20) & 0x1f)
> +
> +#define branch_funct3(opcode) \
> + (((opcode) >> 12) & 0x7)
> +
> +#define branch_imm(opcode) \
> + (((((opcode) >> 8 ) & 0xf ) << 1 ) | \
> + ((((opcode) >> 25) & 0x3f) << 5 ) | \
> + ((((opcode) >> 7 ) & 0x1 ) << 11) | \
> + ((((opcode) >> 31) & 0x1 ) << 12))
> +
> +#define branch_offset(opcode) \
> + sign_extend32((branch_imm(opcode)), 12)
> +
> +#define BRANCH_BEQ 0x0
> +#define BRANCH_BNE 0x1
> +#define BRANCH_BLT 0x4
> +#define BRANCH_BGE 0x5
> +#define BRANCH_BLTU 0x6
> +#define BRANCH_BGEU 0x7
> +
> +bool __kprobes simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *regs)
> +{
> + /*
> + * branch instructions:
> + * 31 30 25 24 20 19 15 14 12 11 8 7 6 0
> + * | imm[12] | imm[10:5] | rs2 | rs1 | funct3 | imm[4:1] | imm[11] | opcode |
> + * 1 6 5 5 3 4 1 7
> + * imm[12|10:5] rs2 rs1 000 imm[4:1|11] 1100011 BEQ
> + * imm[12|10:5] rs2 rs1 001 imm[4:1|11] 1100011 BNE
> + * imm[12|10:5] rs2 rs1 100 imm[4:1|11] 1100011 BLT
> + * imm[12|10:5] rs2 rs1 101 imm[4:1|11] 1100011 BGE
> + * imm[12|10:5] rs2 rs1 110 imm[4:1|11] 1100011 BLTU
> + * imm[12|10:5] rs2 rs1 111 imm[4:1|11] 1100011 BGEU
> + */
> +
> + s32 offset;
> + s32 offset_tmp;
> + unsigned long rs1_val;
> + unsigned long rs2_val;
> +
> + if (!rv_insn_reg_get_val(regs, branch_rs1_idx(opcode), &rs1_val) ||
> + !rv_insn_reg_get_val(regs, branch_rs2_idx(opcode), &rs2_val))
> + return false;
> +
> + offset_tmp = branch_offset(opcode);
> + switch (branch_funct3(opcode)) {
> + case BRANCH_BEQ:
> + offset = (rs1_val == rs2_val) ? offset_tmp : 4;
> + break;
> + case BRANCH_BNE:
> + offset = (rs1_val != rs2_val) ? offset_tmp : 4;
> + break;
> + case BRANCH_BLT:
> + offset = ((long)rs1_val < (long)rs2_val) ? offset_tmp : 4;
> + break;
> + case BRANCH_BGE:
> + offset = ((long)rs1_val >= (long)rs2_val) ? offset_tmp : 4;
> + break;
> + case BRANCH_BLTU:
> + offset = (rs1_val < rs2_val) ? offset_tmp : 4;
> + break;
> + case BRANCH_BGEU:
> + offset = (rs1_val >= rs2_val) ? offset_tmp : 4;
> + break;
> + default:
> + return false;
> + }
> +
> + instruction_pointer_set(regs, addr + offset);
> +
> + return true;
> +}
>

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