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    SubjectRe: [PATCH v5 7/9] riscv/kprobe: Prepare detour buffer for optimized kprobe
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    在 2023/1/4 17:12, Björn Töpel 写道:
    > "liaochang (A)" <liaochang1@huawei.com> writes:
    >
    >>>> +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.
    >
    > What I meant was that "nop" can expand to compressed instructions, and
    > you should be explicit. So you know how it's expanded by the
    > compiler/assembler.
    >
    > An example:
    >
    > $ cat bar.S
    > .text
    > bar:
    > nop
    > nop
    > $ riscv64-linux-gnu-gcc -O2 -o bar.o -c bar.S && riscv64-linux-gnu-objdump -M no-aliases -d bar.o
    >
    > bar.o: file format elf64-littleriscv
    >
    >
    > Disassembly of section .text:
    >
    > 0000000000000000 <bar>:
    > 0: 0001 c.addi zero,0
    > 2: 0001 c.addi zero,0
    >
    >
    > vs
    >
    > $ cat foo.S
    > .text
    > foo:
    > .option norvc
    > nop
    > nop
    >
    > $ riscv64-linux-gnu-gcc -O2 -o foo.o -c foo.S && riscv64-linux-gnu-objdump -M no-aliases -d foo.o
    >
    > foo.o: file format elf64-littleriscv
    >
    >
    > Disassembly of section .text:
    >
    > 0000000000000000 <foo>:
    > 0: 00000013 addi zero,zero,0
    > 4: 00000013 addi zero,zero,0

    Above examples are very clear, i will use these expaned instructions in next revision, thanks.

    >
    >
    > Björn

    --
    BR,
    Liao, Chang

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