Re: [Qemu-riscv] [Qemu-devel] [PATCH] RISC-V: fix single stepping over ret and other branching instructions

[Richard Henderson]

On 3/22/19 4:22 AM, Fabien Chouteau wrote:
> +/* Wrapper around tcg_gen_exit_tb that handles single stepping */
> +static void exit_tb(DisasContext *ctx, TranslationBlock *tb, unsigned idx)
> +{
> +    if (ctx->base.singlestep_enabled) {
> +        gen_exception_debug();
> +    } else {
> +        tcg_gen_exit_tb(tb, idx);
> +    }
> +}

You should remove the TB and idx parameters here and pass NULL, 0 to
tcg_gen_exit_tb.

> @@ -138,14 +158,10 @@ static void gen_goto_tb(DisasContext *ctx, int n, 
> target_ulong dest)
>          /* chaining is only allowed when the jump is to the same page */
>          tcg_gen_goto_tb(n);
>          tcg_gen_movi_tl(cpu_pc, dest);
> -        tcg_gen_exit_tb(ctx->base.tb, n);
> +        exit_tb(ctx, ctx->base.tb, n);

Because this is the only non-zero use, and it is already protected by
use_goto_tb, which includes the single-step check.

Because goto_tb(n) must be paired with exit_tb(tb, n), and vice-versa.


r~