linux-kernel - Re: [PATCH] selftests: kvm: Fix a compile error in selftests/kvm/rseq

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Message-ID: <YuqeDetNukKp9lyF@google.com>
Date:   Wed, 3 Aug 2022 16:10:53 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Andrew Jones <andrew.jones@...ux.dev>
Cc:     Jinrong Liang <ljr.kernel@...il.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Jinrong Liang <cloudliang@...cent.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] selftests: kvm: Fix a compile error in
 selftests/kvm/rseq_test.c

On Wed, Aug 03, 2022, Andrew Jones wrote:
> On Wed, Aug 03, 2022 at 09:58:51PM +0800, Jinrong Liang wrote:
> > My ldd version is (GNU libc) 2.28, and I get a compilation error in this case.
> > But I use another ldd (Ubuntu GLIBC 2.31-0ubuntu9.2) 2.31 is compiling fine.
> > This shows that compilation errors may occur in different GNU libc environments.
> > Would it be more appropriate to use syscall for better compatibility?
> 
> OK, it's a pity, but no big deal to use syscall().

Ya, https://man7.org/linux/man-pages/man2/gettid.2.html says:

  The gettid() system call first appeared on Linux in kernel 2.4.11.  Library
  support was added in glibc 2.30.

But there are already two other instances of syscall(SYS_gettid) in KVM selftests,
tools/testing/selftests/kvm/lib/assert.c even adds a _gettid() wrapper.

So rather than having to remember (or discover) to use syscall(SYS_gettid), I wonder
if it's possible to conditionally define gettid()?  E.g. check for GLIBC version?
Or do

  #define gettid() syscall(SYS_gettid)

so that it's always available and simply overrides the library's gettid() if it's
provided?