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

["Darrick J. Wong" <djwong@kernel.org>]

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.

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 $<
 
 # 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;
+}