Messages in this thread | | | Date | Thu, 5 Jan 2023 08:46:07 +0800 | Subject | Re: [PATCH v5 7/9] riscv/kprobe: Prepare detour buffer for optimized kprobe | From | "liaochang (A)" <> |
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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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