Re: [PATCH] selftests: kvm: Fix a compile error in selftests/kvm/rseq_test.c

From: Sean Christopherson <seanjc@google.com>
To: Andrew Jones <andrew.jones@linux.dev>
Cc: Jinrong Liang <ljr.kernel@gmail.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Joerg Roedel <joro@8bytes.org>,
	Jinrong Liang <cloudliang@tencent.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] selftests: kvm: Fix a compile error in selftests/kvm/rseq_test.c
Date: Wed, 3 Aug 2022 16:10:53 +0000	[thread overview]
Message-ID: <YuqeDetNukKp9lyF@google.com> (raw)
In-Reply-To: <20220803142637.3y5fj2cwyvbrwect@kamzik>

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?