From: Sean Christopherson <seanjc@google.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Marc Zyngier <maz@kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Nathan Chancellor <nathan@kernel.org>,
James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Oliver Upton <oliver.upton@linux.dev>, Tom Rix <trix@redhat.com>,
kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
linux-riscv@lists.infradead.org, llvm@lists.linux.dev,
linux-kernel@vger.kernel.org,
Ricardo Koller <ricarkol@google.com>,
Aaron Lewis <aaronlewis@google.com>,
Raghavendra Rao Ananta <rananta@google.com>
Subject: Re: [PATCH 11/14] KVM: selftests: Disable "gnu-variable-sized-type-not-at-end" warning
Date: Tue, 13 Dec 2022 02:13:25 +0000 [thread overview]
Message-ID: <Y5ffxebJ/eRzEXh+@google.com> (raw)
In-Reply-To: <CAKwvOdnRQQb9YbH=MgDymBmmjYgajc8tkyjbJVxjpA5zDZpNTQ@mail.gmail.com>
On Mon, Dec 12, 2022, Nick Desaulniers wrote:
> > diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> > index 2487db21b177..9cff99a1cb2e 100644
> > --- a/tools/testing/selftests/kvm/Makefile
> > +++ b/tools/testing/selftests/kvm/Makefile
> > @@ -196,6 +196,7 @@ else
> > LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
> > endif
> > CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
> > + -Wno-gnu-variable-sized-type-not-at-end \
>
> This is a clang-specific warning. This will need to be wrapped in a
> cc-option check.
Not that I'm against guarding this code, but I don't think cc-option() will do
anything in this case.
AFAICT, gcc stopped treating unknown "-Wno" flags as unconditional errors starting
with gcc-4.4, and the kernel's min supported version is 5.1. gcc-4.4 through
gcc-9.5 all print a mild warning if there's a different error, but otherwise
silently ignore the uknown "-Wno".
cc1: warning: unrecognized command line option '-Wno-gnu-variable-sized-type-not-at-end'
gcc-10.1 is even friendlier and notes that the unknown flag may have been related
to the error.
cc1: note: unrecognized command-line option '-Wno-gnu-variable-sized-type-not-at-end'
may have been intended to silence earlier diagnostics
Because cc-option() doesn't have errors in its probing code, it will return "true"
on gcc for literally any "-Wno-*" input that gcc deems syntacially valid, e.g.
gcc barfs on
depends on $(cc-option,-Wno-)
depends on $(cc-option,-Wno)
but happily succeeds with
depends on $(cc-option,-Wno-lol-gcc)
Various man pages suggest -Wunknown-warnings is a thing, but no gcc version
supported by godbolt recognizes it.
So unless I'm missing something, trying to detect lack of support will be non-trivial,
and the worst case scenario is that users of older gcc version will see a potentially
confusing warning when the build fails.
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next prev parent reply other threads:[~2022-12-13 2:14 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-13 0:16 [PATCH 00/14] KVM: selftests: Clang fixes, Makefile cleanup Sean Christopherson
2022-12-13 0:16 ` [PATCH 01/14] KVM: selftests: Define literal to asm constraint in aarch64 as unsigned long Sean Christopherson
2022-12-13 9:51 ` Philippe Mathieu-Daudé
2022-12-13 0:16 ` [PATCH 02/14] KVM: selftests: Delete dead code in x86_64/vmx_tsc_adjust_test.c Sean Christopherson
2022-12-13 0:16 ` [PATCH 03/14] KVM: selftests: Fix divide-by-zero bug in memslot_perf_test Sean Christopherson
2022-12-13 9:46 ` Philippe Mathieu-Daudé
2022-12-13 0:16 ` [PATCH 04/14] KVM: selftests: Use pattern matching in .gitignore Sean Christopherson
2022-12-13 0:16 ` [PATCH 05/14] KVM: selftests: Fix a typo in x86-64's kvm_get_cpu_address_width() Sean Christopherson
2022-12-13 9:47 ` Philippe Mathieu-Daudé
2022-12-13 0:16 ` [PATCH 06/14] KVM: selftests: Rename UNAME_M to ARCH_DIR, fill explicitly for x86 Sean Christopherson
2022-12-13 20:03 ` Sean Christopherson
2022-12-14 9:43 ` Marc Zyngier
2022-12-24 9:12 ` Paolo Bonzini
2022-12-13 0:16 ` [PATCH 07/14] KVM: selftests: Use proper function prototypes in probing code Sean Christopherson
2022-12-13 9:48 ` Philippe Mathieu-Daudé
2022-12-13 0:16 ` [PATCH 08/14] KVM: selftests: Probe -no-pie with actual CFLAGS used to compile Sean Christopherson
2022-12-13 0:16 ` [PATCH 09/14] KVM: selftests: Explicitly disable builtins for mem*() overrides Sean Christopherson
2022-12-24 9:16 ` Paolo Bonzini
2022-12-13 0:16 ` [PATCH 10/14] KVM: selftests: Include lib.mk before consuming $(CC) Sean Christopherson
2022-12-24 9:18 ` Paolo Bonzini
2022-12-13 0:16 ` [PATCH 11/14] KVM: selftests: Disable "gnu-variable-sized-type-not-at-end" warning Sean Christopherson
2022-12-13 1:36 ` Nick Desaulniers
2022-12-13 2:13 ` Sean Christopherson [this message]
2023-01-11 16:23 ` Paolo Bonzini
2022-12-13 0:16 ` [PATCH 12/14] KVM: selftests: Use wildcards to find library source files Sean Christopherson
2022-12-24 9:23 ` Paolo Bonzini
2023-01-04 1:09 ` Sean Christopherson
2022-12-13 0:16 ` [PATCH 13/14] KVM: selftests: Use wildcards to find targets and test " Sean Christopherson
2022-12-13 0:16 ` [PATCH 14/14] KVM: selftests: Enable RSEQ test for RISC-V Sean Christopherson
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