From: Segher Boessenkool <segher@kernel.crashing.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: masahiroy@kernel.org, nicolas@fjasle.eu,
linux-kbuild@vger.kernel.org, trix@redhat.com,
llvm@lists.linux.dev, ndesaulniers@google.com, npiggin@gmail.com,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 07/14] powerpc/vdso: Improve linker flags
Date: Mon, 23 Jan 2023 09:07:16 -0600 [thread overview]
Message-ID: <20230123150716.GJ25951@gate.crashing.org> (raw)
In-Reply-To: <20221228-drop-qunused-arguments-v2-7-9adbddd20d86@kernel.org>
Hi!
On Wed, Jan 11, 2023 at 08:05:04PM -0700, Nathan Chancellor wrote:
> When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, there
> are several warnings in the PowerPC vDSO:
>
> clang-16: error: -Wl,-soname=linux-vdso32.so.1: 'linker' input unused [-Werror,-Wunused-command-line-argument]
> clang-16: error: -Wl,--hash-style=both: 'linker' input unused [-Werror,-Wunused-command-line-argument]
> clang-16: error: argument unused during compilation: '-shared' [-Werror,-Wunused-command-line-argument]
>
> clang-16: error: argument unused during compilation: '-nostdinc' [-Werror,-Wunused-command-line-argument]
> clang-16: error: argument unused during compilation: '-Wa,-maltivec' [-Werror,-Wunused-command-line-argument]
There is nothing wrong with the warnings, but as usual, -Werror is very
counterproductive.
> The first group of warnings point out that linker flags were being added
> to all invocations of $(CC), even though they will only be used during
> the final vDSO link. Move those flags to ldflags-y.
Which is explicitly allowed, and won't do anything, so nothing harmful
either. It is not a bad idea to avoid this if that is trivial to do,
of course.
> The second group of warnings are compiler or assembler flags that will
> be unused during linking. Filter them out from KBUILD_CFLAGS so that
> they are not used during linking.
And here it is even more obviously fine. If you need obfuscation like
in your patch, it is better not to do this imo.
The warning text "linker input unused" is misleading btw. It would be
good to warn about that, if it was true: very likely the user didn't
intend what he wrote. But a linker input is an object file, or perhaps
a linker script. These things are just compiler flags.
Segher
next prev parent reply other threads:[~2023-01-23 15:17 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-12 3:04 [PATCH v2 00/14] Remove clang's -Qunused-arguments from KBUILD_CPPFLAGS Nathan Chancellor
2023-01-12 3:04 ` [PATCH v2 01/14] x86/boot/compressed: prefer cc-option for CFLAGS additions Nathan Chancellor
2023-01-12 3:04 ` [PATCH v2 02/14] MIPS: Always use -Wa,-msoft-float and eliminate GAS_HAS_SET_HARDFLOAT Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 03/14] MIPS: Prefer cc-option for additions to cflags Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 04/14] kbuild: Update assembler calls to use proper flags and language target Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 05/14] powerpc: Remove linker flag from KBUILD_AFLAGS Nathan Chancellor
2023-01-25 4:11 ` Michael Ellerman
2023-01-26 1:29 ` Masahiro Yamada
2023-01-26 2:07 ` Nathan Chancellor
2023-01-26 4:22 ` Masahiro Yamada
2023-01-26 10:05 ` Michael Ellerman
2023-01-12 3:05 ` [PATCH v2 06/14] powerpc/vdso: Remove unused '-s' flag from ASFLAGS Nathan Chancellor
2023-01-25 4:12 ` Michael Ellerman
2023-01-12 3:05 ` [PATCH v2 07/14] powerpc/vdso: Improve linker flags Nathan Chancellor
2023-01-12 18:02 ` Sedat Dilek
2023-01-12 18:21 ` Nathan Chancellor
2023-01-12 18:47 ` Sedat Dilek
2023-01-22 17:27 ` Masahiro Yamada
2023-01-22 18:01 ` Nathan Chancellor
2023-01-23 15:07 ` Segher Boessenkool [this message]
2023-01-24 16:14 ` Nathan Chancellor
2023-01-24 16:30 ` Segher Boessenkool
2023-01-12 3:05 ` [PATCH v2 08/14] powerpc/vdso: Remove an unsupported flag from vgettimeofday-32.o with clang Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 09/14] s390/vdso: Drop unused '-s' flag from KBUILD_AFLAGS_64 Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 10/14] s390/vdso: Drop '-shared' from KBUILD_CFLAGS_64 Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 11/14] s390/purgatory: Remove unused '-MD' and unnecessary '-c' flags Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 12/14] drm/amd/display: Do not add '-mhard-float' to dml_ccflags for clang Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 13/14] kbuild: Turn a couple more of clang's unused option warnings into errors Nathan Chancellor
2023-01-12 3:05 ` [PATCH v2 14/14] kbuild: Stop using '-Qunused-arguments' with clang Nathan Chancellor
2023-01-22 17:28 ` [PATCH v2 00/14] Remove clang's -Qunused-arguments from KBUILD_CPPFLAGS Masahiro Yamada
2023-01-23 13:58 ` Naresh Kamboju
2023-01-23 16:11 ` Nathan Chancellor
2023-01-24 15:29 ` Naresh Kamboju
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