Re: [PATCH v2] target/riscv: Update $ra with current $pc in trans_cm_jalt()

[Richard Henderson]

On 2/6/24 22:18, Jason Chien wrote:
> The original implementation sets $pc to the address read from the jump
> vector table first and links $ra with the address of the next instruction
> after the updated $pc. After jumping to the updated $pc and executing the
> next ret instruction, the program jumps to $ra, which is in the same
> function currently executing, which results in an infinite loop.
> This commit stores the jump address in a temporary, updates $ra with the
> current $pc, and copies the temporary to $pc.
>
> Signed-off-by: Jason Chien <jason.chien@sifive.com>
> Reviewed-by: Frank Chang <frank.chang@sifive.com>
> ---
>   target/riscv/insn_trans/trans_rvzce.c.inc | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~

> diff --git a/target/riscv/insn_trans/trans_rvzce.c.inc 
> b/target/riscv/insn_trans/trans_rvzce.c.inc
> index 2d992e14c4..cd234ad960 100644
> --- a/target/riscv/insn_trans/trans_rvzce.c.inc
> +++ b/target/riscv/insn_trans/trans_rvzce.c.inc
> @@ -293,12 +293,14 @@ static bool trans_cm_jalt(DisasContext *ctx, arg_cm_jalt 
> *a)
>   {
>       REQUIRE_ZCMT(ctx);
>   
> +    TCGv addr = tcg_temp_new();
> +
>       /*
>        * Update pc to current for the non-unwinding exception
>        * that might come from cpu_ld*_code() in the helper.
>        */
>       gen_update_pc(ctx, 0);
> -    gen_helper_cm_jalt(cpu_pc, tcg_env, tcg_constant_i32(a->index));
> +    gen_helper_cm_jalt(addr, tcg_env, tcg_constant_i32(a->index));
>   
>       /* c.jt vs c.jalt depends on the index. */
>       if (a->index >= 32) {
> @@ -307,6 +309,8 @@ static bool trans_cm_jalt(DisasContext *ctx, arg_cm_jalt *a)
>           gen_set_gpr(ctx, xRA, succ_pc);
>       }
>   
> +    tcg_gen_mov_tl(cpu_pc, addr);
> +
>       tcg_gen_lookup_and_goto_ptr();
>       ctx->base.is_jmp = DISAS_NORETURN;
>       return true;