From: Jason Chien <jason.chien@sifive.com>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org,
Palmer Dabbelt <palmer@dabbelt.com>,
Alistair Francis <alistair.francis@wdc.com>,
Bin Meng <bin.meng@windriver.com>,
Weiwei Li <liweiwei@iscas.ac.cn>,
Daniel Henrique Barboza <dbarboza@ventanamicro.com>,
Liu Zhiwei <zhiwei_liu@linux.alibaba.com>,
Junqiang Wang <wangjunqiang@iscas.ac.cn>
Subject: Re: [PATCH] target/riscv: Update $pc after linking to $ra in trans_cm_jalt()
Date: Wed, 7 Feb 2024 11:33:51 +0800 [thread overview]
Message-ID: <CADr__8rwLz7=FvkCwncRy4fGsHYxe0BXEstB_1o_P14p37ZmYA@mail.gmail.com> (raw)
In-Reply-To: <162e0b5c-ed98-4e84-af6e-9fdaea0dcc04@linaro.org>
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You are right. I'll send patch v2 shortly. Thank you for the reply.
Richard Henderson <richard.henderson@linaro.org> 於 2024年2月7日 週三 上午4:24寫道：
> On 2/6/24 23:18, 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 reverses the two action. Firstly, $ra is updated with the
> > address of the next instruction after $pc, and sets $pc to the address
> > read from the jump vector table.
>
> This is unlikely to be correct in the case the vector table read faults,
> leaving $ra updated.
>
> I guess this got broken with CF_PCREL. Anyway, the solution is to use a
> temporary...
>
> > - /*
> > - * 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, cpu_env, tcg_constant_i32(a->index));
>
> ... here and then ...
>
> > @@ -307,6 +300,13 @@ static bool trans_cm_jalt(DisasContext *ctx,
> arg_cm_jalt *a)
> > gen_set_gpr(ctx, xRA, succ_pc);
> > }
> >
>
> ... copy the temp to cpu_pc here.
>
> > tcg_gen_lookup_and_goto_ptr();
> > ctx->base.is_jmp = DISAS_NORETURN;
> > return true;
>
>
>
> r~
>
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prev parent reply other threads:[~2024-02-07 3:33 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-06 13:18 [PATCH] target/riscv: Update $pc after linking to $ra in trans_cm_jalt() Jason Chien
2024-02-06 17:05 ` Frank Chang
2024-02-06 20:24 ` Richard Henderson
2024-02-07 3:33 ` Jason Chien [this message]
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