On Mon, Sep 06, 2021 at 02:08:58PM -0700, Linus Torvalds wrote:

On Mon, Sep 6, 2021 at 1:14 PM Jakub Jelinek [off-list ref] wrote:

quoted

the only guaranteed APIs are
those provided by the headers (x86intrin.h/*mmintrin.h etc. on x86,
arm_{neon,sve}.h etc. on arm*, ...)

You guys realize we don't use those, do you?

Linux does use the Arm and Power vector intrinsics (arm_neon.h and
altivec.h).

And you don't seem to realize that you are actively arguing *AGAINST*
what you think you argue for.

I have no idea what you think we are arguing for, only what we are.

That "immintrin.h" file, for example, is simply not usable for the
kernel. I just checked.

Yes.  It cannot be used in freestanding environments; it includes a
header file we don't ship (<mm_malloc.h>, via <xmmintrin.h>).  Or
perhaps we do ship it, but only on native systems?  Same issue, anyway.

The top comment in the latter says
  /* Implemented from the specification included in the Intel C++ Compiler
     User Guide and Reference, version 9.0.  */
so the shortcoming exists there already probably?

      27 | #include <stdlib.h>
         |          ^~~~~~~~~~

Oops.

Yup, that is not a (freestanding) standard C header.

Very similar things happens if you try to use that <stdint.h> file
that somebody mentioned earlier.

Not at all.  <stdint.h> *is* a standard C header, and we ship it, it
always works.  If you find problems with it, please report them!

You also don't seem to realize how hard it is to separate out the
user-land crap that we really cannot use, and must not use.

We have worked very hard for many years to make this better.  For the
freestanding headers only <limits.h> is still problematic, and you do
not need that one anyway, it is legacy more than anything else.


Segher