linux-kernel - Re: [PATCH v1] LoongArch: Remove unnecessary checks in bt

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Message-ID: <CAAhV-H4UpzqUiEi7Qfc2qtU1hm=yR9hYfaUGfrAtQssrk6qWOA@mail.gmail.com>
Date: Sat, 13 Dec 2025 20:24:38 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Bibo Mao <maobibo@...ngson.cn>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] LoongArch: Remove unnecessary checks in bt_address()

On Wed, Dec 10, 2025 at 4:00 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> On 2025/12/10 上午10:25, Bibo Mao wrote:
> >
> >
> > On 2025/12/10 上午9:28, Tiezhu Yang wrote:
> >> On 2025/12/9 下午4:30, Huacai Chen wrote:
> >>> Hi, Tiezhu,
> >>>
> >>> On Tue, Dec 9, 2025 at 2:18 PM Tiezhu Yang <yangtiezhu@...ngson.cn>
> >>> wrote:
> >>>>
> >> ...
> >>>>          extern unsigned long eentry;
> >>>>
> >>>> -       if (__kernel_text_address(ra))
> >>>> -               return ra;
> >>>> -
> >>>> -       if (__module_text_address(ra))
> >>>> -               return ra;
> >>> I think the correct way is to remove the __module_text_address()
> >>> condition but keep the __kernel_text_address() condition. Then return
> >>> 0 at the end of this function, and remove the __kernel_text_address()
> >>> condition out of this function.
> >>
> >> It can not remove the check of __kernel_text_address() after calling
> >> bt_address() because it needs to validate the calculated address for
> >> exception, then no need to keep the __kernel_text_address() condition
> >> in bt_address() because it will check the PC outside bt_address().
> >          state->pc = bt_address(pc);
> >          if (!state->pc) {
> >                  pr_err("cannot find unwind pc at %p\n", (void *)pc);
> >                  goto err;
> >          }
> >
> >          if (!__kernel_text_address(state->pc))
> >                  goto err;
> > I guess that you both comes from different views :) one treats these
> > piece of code into one, one only views function bt_address().
> >
> > Especially with if (!state->pc), how could this happen?
>
> IMO, state->pc will be not 0 forever in practice, this check is just an
> error path and can be removed too if possible.
bt_address() return ra both in "good path" and "bad path" is strange.
I still suggest using my method, but move __kernel_text_address()
after the "if (ra >= eentry && ra < eentry +  EXCCODE_INT_END *
VECSIZE)" block to verify the modified ra.

Huacai

>
> Thanks,
> Tiezhu
>