build-sys: Switch to clang by default

Eventually we want to do cross-language LTO: https://developers.redhat.com/blog/2020/03/18/cross-language-link-time-optimization-using-red-hat-developer-tools/ But in the immediate term, using clang/lld instead of ld.bfd (or ld.gold) works around a linker bug: #2518 (comment)
coreos · Feb 1, 2021 · 5f82919 · 5f82919
1 parent bccde5f
commit 5f82919
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Showing 3 changed files with 19 additions and 12 deletions.
diff --git a/Makefile-lib.am b/Makefile-lib.am
@@ -36,10 +36,6 @@ librpmostree_1_la_CFLAGS = $(AM_CFLAGS) -I$(srcdir)/libglnx -I$(srcdir)/src/libp
 librpmostree_1_la_LDFLAGS = $(AM_LDFLAGS) -version-number 1:0:0 -Bsymbolic-functions
 librpmostree_1_la_LIBADD =  $(PKGDEP_LIBRPMOSTREE_LIBS) libglnx.la
 
-# XXX: work around clang being passed -fstack-clash-protection which it doesn't understand
-# https://github.com/projectatomic/rpm-ostree/pull/1787#issuecomment-473971585
-INTROSPECTION_SCANNER_ENV = CC=gcc
-
 if BUILDOPT_INTROSPECTION
 RpmOstree-1.0.gir: librpmostree-1.la Makefile
 RpmOstree_1_0_gir_EXPORT_PACKAGES = rpm-ostree-1

diff --git a/ci/build.sh b/ci/build.sh
@@ -13,5 +13,7 @@ ${dn}/installdeps.sh
 rustc --version
 
 export LSAN_OPTIONS=verbosity=1:log_threads=1
-# And now the build
+# And now the build; we use clang by default.  For more information
+# see the spec file.
+export CC=clang CXX=clang++ LD=/usr/bin/ld.lld RUSTFLAGS="-C link-arg=-fuse-ld=lld"
 build --enable-installed-tests --enable-gtk-doc ${CONFIGOPTS:-}
diff --git a/packaging/rpm-ostree.spec.in b/packaging/rpm-ostree.spec.in
@@ -13,7 +13,19 @@ Source0: https://github.com/coreos/rpm-ostree/releases/download/v%{version}/rpm-
 
 ExclusiveArch: %{rust_arches}
 
+# rpm-ostree is a hybrid C/C++/Rust program; currently using autotools:
+# We always run autogen.sh
+BuildRequires: autoconf automake libtool git
 BuildRequires: make
+# Use LLVM by default for multiple reasons.
+# First, eventually we want to do cross-language LTO:
+# https://developers.redhat.com/blog/2020/03/18/cross-language-link-time-optimization-using-red-hat-developer-tools/
+# But in the immediate term, using clang/lld instead of ld.bfd (or ld.gold)
+# works around a linker bug: https://github.com/coreos/rpm-ostree/pull/2518#issuecomment-770918530
+# also xref https://github.com/rust-lang/rust/issues/53945#issuecomment-425620542
+BuildRequires: clang lld
+
+# Rust dependencies.
 %if 0%{?rhel} && !0%{?eln}
 BuildRequires: rust-toolset
 %else
@@ -37,8 +49,6 @@ BuildRequires: rust
 
 # For the autofiles bits below
 BuildRequires: /usr/bin/python3
-# We always run autogen.sh
-BuildRequires: autoconf automake libtool git
 # For docs
 BuildRequires: chrpath
 BuildRequires: gtk-doc
@@ -66,10 +76,6 @@ BuildRequires: pkgconfig(expat)
 BuildRequires: pkgconfig(check)
 BuildRequires: pkgconfig(libsolv)
 
-# We need g++ for libdnf
-BuildRequires: gcc-c++
-
-
 # more libdnf build deps (see libdnf's spec for versions)
 %global swig_version 3.0.12
 %global libmodulemd_version 2.5.0
@@ -130,7 +136,10 @@ env NOCONFIGURE=1 ./autogen.sh
 # Since we're hybrid C++/Rust we need to propagate this manually;
 # the %%configure macro today assumes (reasonably) that one is building
 # C/C++ and sets C{,XX}FLAGS
-export RUSTFLAGS="%{build_rustflags}"
+# FIXME uncomment and debug this
+# export RUSTFLAGS="%{build_rustflags}"
+# See comment in the BuildRequires for why we use clang
+export CC=clang CXX=clang++ LD=/usr/bin/ld.lld RUSTFLAGS="-C link-arg=-fuse-ld=lld"
 %configure --disable-silent-rules --enable-gtk-doc %{?sqlite_rpmdb_default}
 %make_build