linux-kernel - Re: [PATCH v3 0/6] mips: system call table generation support

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Date:   Thu, 06 Dec 2018 19:10:57 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     "Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:     Joseph Myers <joseph@...esourcery.com>,
        Paul Burton <paul.burton@...s.com>,
        Firoz Khan <firoz.khan@...aro.org>,
        "open list\:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>,
        libc-alpha@...rceware.org
Subject: Re: [PATCH v3 0/6] mips: system call table generation support

* Maciej W. Rozycki:

> On Thu, 6 Dec 2018, Joseph Myers wrote:
>
>> >  So how are `SYS_<name>' macros generated that land in <bits/syscall.h>?
>> 
>> By gen-syscall-h.awk, which generates #ifdef conditionals for each 
>> possible __NR_* name (as listed in syscall-names.list in glibc).
>
>  I seem to remember having to take extra care with how the three MIPS ABIs 
> wire the syscalls to get it right in glibc, but I take it then this has 
> been now addressed reliably enough for the glibc not to care how exactly
> <asm/unistd.h> has been arranged.

This is a fairly recent change (commit
2dba5ce7b8115d6a2789bf279892263621088e74, "<bits/syscall.h>: Use an
arch-independent system call list on Linux", first release with it is
glibc 2.27).  This patch is quite backportable; we have put it into our
2.17-derived glibc, and the upstream work was originally driven by
downstream ordering requirements of kernel header and glibc builds.
Glad to see it's useful elsewhere.

The test retains the old <asm/unistd.h>-based macro extraction for
testing purposes, but it needs that only for the actual target
architecture and only the *names*, so it's easy to implement.  Before
that, the generation would have to carefully take into account multiple
sub-targets (i386/x86-64/x32 is one of the more complicated scenarios).
Presumably, you saw problem with that part.

Even if you introduce breakage here, it will only affect older glibc
builds.  It's not something that application developers would see.

Thanks,
Florian