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

[Sam James <sam@gentoo.org>]

Sam James <sam@gentoo.org> writes:

> "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.

... thinking about this, it could've helped us with
https://lore.kernel.org/linux-xfs/a216140e-1c8a-4d04-ba46-670646498622@redhat.com/

>
> [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