[klibc] [PATCH] Add syscall wrappers required by libkeyutils

[hpa at zytor.com]

On July 27, 2020 6:36:27 PM PDT, Ben Hutchings <ben at decadent.org.uk> wrote:
>On Mon, 2020-07-27 at 05:46 -0700, hpa at zytor.com wrote:
>> On July 27, 2020 2:43:36 AM PDT, Christian Eggers <ceggers at arri.de>
>wrote:
>> > On Saturday, 25 July 2020, 23:36:33 CEST, Ben Hutchings wrote:
>> > > On Wed, 2020-07-08 at 08:37 +0200, Christian Eggers wrote:
>> > > > ...
>> > > > libkeyutils usually invokes syscall() directly. As syscall() is
>not
>> > > > provided by klibc, libkeyutils has to be slightly modified for
>using the
>> > > > klibc wrappers.
>> > > 
>> > > Wouldn't it be more useful for klibc to implement syscall() then?
>> > 
>> > I hope that somebody else could respond to this question as I am
>likely not
>> > skilled enough to answer this.
>[...]
>> syscall(3) is not implemented by design, because it is silently
>> broken on many architectures (mainly 32-bit ones.)
>
>I understand that it's not portable in general, as there are many
>architecture-specific quirks in the system call ABI.  But where there
>are other established libraries using it, I assume they're already
>dealing with those quirks.  Also, the newer system calls that are
>likely to be called this way are less quirky, aren't they?
>
>I think that if we can *cheaply* implement a glibc API that allows more
>software to build and run on klibc with fewer changes, then we should.
>
>Ben.

I'm not so sure they have dealt with it in the sense of having it work on all architectures. *Most* of the problems are related to the shifting the arguments by one, which can cause a bunch of problems, especially if it means the arguments spill to memory. However, I have absolutely no idea how to correctly implement syscall(3) on s390 without a full table.

It is of course possible to implement using stdarg.h and a big switch statement, but that is anything but cheap.

Now, thinking about it, it *might* be possible to implement some of this using varadic macros. Let me play around with it a little bit.

-- 
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