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

[Tiezhu Yang]

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.

[1] 
https://gcc.gnu.org/onlinedocs/gcc/LoongArch-Base-Built-in-Functions.html

Thanks,
Tiezhu