On Thu, Feb 22, 2024 at 12:53 AM Leon Hwang <hffilwlqm@xxxxxxxxx> wrote:
>
> +DEFINE_PER_CPU(u32, bpf_tail_call_cnt);
> +
> +static __used void bpf_tail_call_cnt_prepare(void)
> +{
> + /* The following asm equals to
> + *
> + * u32 *tcc_ptr = this_cpu_ptr(&bpf_tail_call_cnt);
> + *
> + * *tcc_ptr = 0;
> + *
> + * This asm must uses %rax only.
> + */
> +
> + asm volatile (
> + "addq " __percpu_arg(0) ", %1\n\t"
> + "movl $0, (%%rax)\n\t"
This looks wrong.
Should probably be "movl $0, (%1)" ?
> + :
> + : "m" (this_cpu_off), "r" (&bpf_tail_call_cnt)
> + );
> +}
> +
> +static __used u32 bpf_tail_call_cnt_fetch_and_inc(void)
> +{
> + u32 tail_call_cnt;
> +
> + /* The following asm equals to
> + *
> + * u32 *tcc_ptr = this_cpu_ptr(&bpf_tail_call_cnt);
> + *
> + * (*tcc_ptr)++;
> + * tail_call_cnt = *tcc_ptr;
> + * tail_call_cnt--;
> + *
> + * This asm must uses %rax only.
> + */
> +
> + asm volatile (
> + "addq " __percpu_arg(1) ", %2\n\t"
> + "incl (%%rax)\n\t"
> + "movl (%%rax), %0\n\t"
and %2 here instead of rax ?
> + "decl %0\n\t"
> + : "=r" (tail_call_cnt)
> + : "m" (this_cpu_off), "r" (&bpf_tail_call_cnt)
> + );
> +
