Re: [PATCH v1] LoongArch: Remove unnecessary checks in bt_address()

[Tiezhu Yang]

On 12/13/25 20:24, Huacai Chen wrote:
> On Wed, Dec 10, 2025 at 4:00 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> > > > > 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.

I am OK if you mean like this:

static inline unsigned long bt_address(unsigned long ra)
{
	extern unsigned long eentry;

	if (ra >= eentry && ra < eentry +  EXCCODE_INT_END * VECSIZE) {
		...
		ra = func + offset;
	}

	if (__kernel_text_address(ra))
		return ra;

	return 0;
}

bool unwind_next_frame(struct unwind_state *state)
{
	...
	state->pc = bt_address(pc);
	if (!state->pc) {
		pr_err("cannot find unwind pc at %p\n", (void *)pc);
		goto err;
	}

	return true;
	...
}

If so, I will send v2 later.

Thanks,
Tiezhu