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

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Message-ID: <19f4722d5cdb90a207129ee675c7278423cd328c.camel@xry111.site>
Date: Tue, 27 May 2025 11:47:19 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] LoongArch: Do not include larchintrin.h

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.

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