linux-kernel - Re: [RFC PATCH] LoongArch: Do not include larchintrin.h

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Message-ID: <CAAhV-H5GEZu=r=gX4afNB2F4w_LpXa1FwuWdyDE=+pGJNnqxww@mail.gmail.com>
Date: Wed, 28 May 2025 21:54:45 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Xi Ruoyao <xry111@...111.site>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] LoongArch: Do not include larchintrin.h

On Tue, May 27, 2025 at 11:47 AM Xi Ruoyao <xry111@...111.site> wrote:
>
> On Tue, 2025-05-27 at 11:17 +0800, Tiezhu Yang wrote:
> > On 2025/5/21 下午1:41, Xi Ruoyao wrote:
> > > On Tue, 2025-05-20 at 14:49 +0800, Tiezhu Yang wrote:
> > > > larchintrin.h is a system header of compiler, include it in the
> > > > kernel header may lead to the fatal error "'larchintrin.h' file
> > > > not found".
> > > >
> > > > There are two related cases so far:
> > > >
> > > > (1) When compiling samples/bpf, it has been fixed in the latest
> > > > kernel [1].
> > > >
> > > > (2) When running bcc script, it has been fixed in the latest
> > > > bcc [2] [3], like this:
> > > >
> > > > $ /usr/share/bcc/tools/filetop
> > > > In file included from <built-in>:4:
> > > > In file included from /virtual/include/bcc/helpers.h:54:
> > > > In file included from arch/loongarch/include/asm/page.h:7:
> > > > In file included from arch/loongarch/include/asm/addrspace.h:9:
> > > > arch/loongarch/include/asm/loongarch.h:11:10: fatal error:
> > > > 'larchintrin.h' file not found
> > > >     11 | #include <larchintrin.h>
> > > >        |          ^~~~~~~~~~~~~~~
> > > > 1 error generated.
> > > >
> > > > Maybe there are same errors for the other unknown projects, it is
> > > > annoyance to add the include path each time. In order to avoid
> > > > such
> > > > errors once and for all, do not include larchintrin.h, just use
> > > > the
> > > > builtin functions directly.
> > >
> > > Sorry, but in GCC those builtin functions are not documented and may
> > > subject to change in the future.  Only the larchintrin.h interface
> > > is
> > > documented.
> >
> > AFAICT, the LoongArch Base Built-in Functions are listed in the GCC
> > documentation [1], they will not be changed easily and frequently in
> > my opinion.
> >
> > __builtin_loongarch_cpucfg()
> > __builtin_loongarch_csrrd_w()
> > __builtin_loongarch_csrrd_d()
> > __builtin_loongarch_csrwr_w()
> > __builtin_loongarch_csrwr_d()
> > __builtin_loongarch_csrxchg_w()
> > __builtin_loongarch_csrxchg_d()
> > __builtin_loongarch_iocsrrd_w()
> > __builtin_loongarch_iocsrrd_d()
> > __builtin_loongarch_iocsrwr_w()
> > __builtin_loongarch_iocsrwr_d()
> >
> > > Thus if you don't want to rely on GCC for those operations, you may
> > > need
> > > to write inline asm...
> >
> > so these builtin functions can be used directly and safely.
>
> Oops, I mistakenly believed they were like __builtin_lsx_* which are not
> documented.
>
> So yes they can be used directly.
I don't think so.

1. csr & iocsr can be only used in kernel mode, if the kernel doesn't
use the convenient short names, then the short names are totally
useless.
2. We get larchintrin.h included by "KBUILD_CFLAGS += -isystem $(shell
$(CC) -print-file-name=include)", and this manner is also used by
other architectures.
3. I don't think there will be many projects that need to be modified.


Huacai

>
> --
> Xi Ruoyao <xry111@...111.site>
> School of Aerospace Science and Technology, Xidian University