Re: [RFC PATCH] libxfs: compile with a C++ compiler

Sam James
2024-08-28T00:01:37Z

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"Darrick J. Wong" <djwong@kernel.org> writes:

> From: Darrick J. Wong <djwong@kernel.org>
>
> Apparently C++ compilers don't like the implicit void* casts that go on
> in the system headers. Compile a dummy program with the C++ compiler to
> make sure this works, so Darrick has /some/ chance of figuring these
> things out before the users do.

Thanks, this is a good idea. Double thanks for the quick fix.

1) yes, it finds the breakage:
Tested-by: Sam James <sam@gentoo.org>

2) with the fix below (CC -> CXX):
Reviewed-by: Sam James <sam@gentoo.org>

3) another thing to think about is:
* -pedantic?
* maybe do one for a bunch of standards? (I think systemd does every
possible value [1])
* doing the above for C as well

I know that sounds a bit like overkill, but systemd
does it and it's cheap to do it versus the blowup if something goes
wrong. I don't have a strong opinion on this or how far you want to go
with it.

[1] https://github.com/systemd/systemd/blob/3317aedff0901e08a8efc8346ad76b184d5d40ea/src/systemd/meson.build#L60

>
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
> configure.ac | 1 +
> include/builddefs.in | 7 +++++++
> libxfs/Makefile | 8 +++++++-
> libxfs/dummy.cpp | 15 +++++++++++++++
> 4 files changed, 30 insertions(+), 1 deletion(-)
> create mode 100644 libxfs/dummy.cpp
>
> diff --git a/configure.ac b/configure.ac
> index 0ffe2e5dfc53..04544f85395b 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -9,6 +9,7 @@ AC_PROG_INSTALL
> LT_INIT
>
> AC_PROG_CC
> +AC_PROG_CXX
> AC_ARG_VAR(BUILD_CC, [C compiler for build tools])
> if test "${BUILD_CC+set}" != "set"; then
> if test $cross_compiling = no; then
> diff --git a/include/builddefs.in b/include/builddefs.in
> index 44f95234d21b..0f312b8b88fe 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -14,6 +14,7 @@ MALLOCLIB = @malloc_lib@
> LOADERFLAGS = @LDFLAGS@
> LTLDFLAGS = @LDFLAGS@
> CFLAGS = @CFLAGS@ -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 -Wno-address-of-packed-member
> +CXXFLAGS = @CXXFLAGS@ -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64 -Wno-address-of-packed-member
> BUILD_CFLAGS = @BUILD_CFLAGS@ -D_FILE_OFFSET_BITS=64 -D_TIME_BITS=64
>
> # make sure we don't pick up whacky LDFLAGS from the make environment and
> @@ -234,9 +235,15 @@ ifeq ($(ENABLE_GETTEXT),yes)
> GCFLAGS += -DENABLE_GETTEXT
> endif
>
> +# Override these if C++ needs other options
> +SANITIZER_CXXFLAGS = $(SANITIZER_CFLAGS)
> +GCXXFLAGS = $(GCFLAGS)
> +PCXXFLAGS = $(PCFLAGS)
> +
> BUILD_CFLAGS += $(GCFLAGS) $(PCFLAGS)
> # First, Sanitizer, Global, Platform, Local CFLAGS
> CFLAGS += $(FCFLAGS) $(SANITIZER_CFLAGS) $(OPTIMIZER) $(GCFLAGS) $(PCFLAGS) $(LCFLAGS)
> +CXXFLAGS += $(FCXXFLAGS) $(SANITIZER_CXXFLAGS) $(OPTIMIZER) $(GCXXFLAGS) $(PCXXFLAGS) $(LCXXFLAGS)
>
> include $(TOPDIR)/include/buildmacros
>
> diff --git a/libxfs/Makefile b/libxfs/Makefile
> index 1185a5e6cb26..bb851ab74204 100644
> --- a/libxfs/Makefile
> +++ b/libxfs/Makefile
> @@ -125,6 +125,8 @@ CFILES = buf_mem.c \
> xfs_trans_space.c \
> xfs_types.c
>
> +LDIRT += dummy.o
> +
> #
> # Tracing flags:
> # -DMEM_DEBUG all zone memory use
> @@ -144,7 +146,11 @@ LTLIBS = $(LIBPTHREAD) $(LIBRT)
> # don't try linking xfs_repair with a debug libxfs.
> DEBUG = -DNDEBUG
>
> -default: ltdepend $(LTLIBRARY)
> +default: ltdepend $(LTLIBRARY) dummy.o
> +
> +dummy.o: dummy.cpp
> + @echo " [CXX] $@"
> + $(Q)$(CC) $(CXXFLAGS) -c $<

$(CXX) ;)

>
> # set up include/xfs header directory
> include $(BUILDRULES)
> diff --git a/libxfs/dummy.cpp b/libxfs/dummy.cpp
> new file mode 100644
> index 000000000000..a872c00ad84b
> --- /dev/null
> +++ b/libxfs/dummy.cpp
> @@ -0,0 +1,15 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2024 Oracle. All Rights Reserved.
> + * Author: Darrick J. Wong <djwong@kernel.org>
> + */
> +#include "include/xfs.h"
> +#include "include/handle.h"
> +#include "include/jdm.h"
> +
> +/* Dummy program to test C++ compilation of user-exported xfs headers */
> +
> +int main(int argc, char *argv[])
> +{
> + return 0;
> +}

cheers,
sam

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