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SubjectRe: [PATCH v4 6/8] riscv/kprobe: Add code to check if kprobe can be optimized
Date
Chen Guokai <chenguokai17@mails.ucas.ac.cn> writes:

[...]

> diff --git a/arch/riscv/kernel/probes/opt.c b/arch/riscv/kernel/probes/opt.c
> index 6d23c843832e..876bec539554 100644
> --- a/arch/riscv/kernel/probes/opt.c
> +++ b/arch/riscv/kernel/probes/opt.c

[...]

> /*
> - * If two free registers can be found at the beginning of both
> - * the start and the end of replaced code, it can be optimized
> - * Also, in-function jumps need to be checked to make sure that
> - * there is no jump to the second instruction to be replaced
> + * The kprobe can be optimized when no in-function jump reaches to the
> + * instructions replaced by optimized jump instructions(AUIPC/JALR).
> */
> static bool can_optimize(unsigned long paddr, struct optimized_kprobe *op)
> {
> - return false;
> + int ret;
> + unsigned long addr, size = 0, offset = 0;
> + struct kprobe *kp = get_kprobe((kprobe_opcode_t *)paddr);
> +
> + /*
> + * Skip optimization if kprobe has been disarmed or instrumented
> + * instruction support XOI.
> + */
> + if (!kp || (riscv_probe_decode_insn(&kp->opcode, NULL) != INSN_GOOD))
> + return false;
> +
> + /*
> + * Find a instruction window large enough to contain a pair
> + * of AUIPC/JALR, and ensure each instruction in this window
> + * supports XOI.
> + */
> + ret = search_copied_insn(paddr, op);
> + if (ret)
> + return false;
> +
> + if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
> + return false;
> +
> + /* Check there is enough space for relative jump(AUIPC/JALR) */
> + if (size - offset <= op->optinsn.length)
> + return false;
> +
> + /*
> + * Decode instructions until function end, check any instruction
> + * don't jump into the window used to emit optprobe(AUIPC/JALR).
> + */

Don't the fixup tables need to be checked, similar to the x86 code?


Björn

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