Hi,
I have been trying to add clang to an existing GNU toolchain, which goal is to
be as isolated from the base system as possible (ie install a working
compiler/assembler/linker/libc in a very specific folder in /opt/MyToolchain
which doesn't use any files from the base system). Also I need to customize
some of the cpp/c/cxx/ldflags used by default in this toolchain.
With gcc, this is quite straight forward since gcc's configure file comes with
handy flags like:
- --with-local-prefix= which allows to override the default system header
include /usr/local/include
- --with-native-system-header-dir= to override the default system header
include /include
--enable-linker-build-id to enable build ids by default (in clang the
equivalent is -DENABLE_LINKER_BUILD_ID)
--with-linker-hash-style=gnu to force the gnu hash style when emitting the
symbol table.
Gcc regularly adds new configure flags as the binutils add new features, so
that you can explicitly enable/disable them from the frontend.
Also gcc comes with its "spec" file which allows to update flag used during the
whole compilation flow, without recompiling gcc itself.
On the other side, when I try to configure clang, it seems much harder to have
a toolchain that:
- is isolated from the base system (my toolchain is not a cross toolchain, it
doesn't use --sysroot, so using a sysroot is not an option)
- allows me to easily customize what are the default ldflags passed to the
linker.
I found out by looking at tools/clang/lib/Driver/ToolChains.cpp that the only
way to achieve that is to, as a packager, maintain patches over the clang
source code. Is this really the way we are meant to properly configure clang
when we don't want to stick to the hardcoded defaults ? Except
-DENABLE_LINKER_BUILD_ID and -DGCC_INSTALL_PREFIX there is not much that seems
to be configurable. What do you advice to packagers with special needs ?
Also why are some flags tied to the distro ? When I see code like this:
if (!IsMips && !IsAndroid) {
if (IsRedhat(Distro) || IsOpenSUSE(Distro) ||
(IsUbuntu(Distro) && Distro >= UbuntuMaverick))
ExtraOpts.push_back("--hash-style=gnu");
if (IsDebian(Distro) || IsOpenSUSE(Distro) || Distro == UbuntuLucid ||
Distro == UbuntuJaunty || Distro == UbuntuKarmic)
ExtraOpts.push_back("--hash-style=both");
}
I wonder why do you check for distro/distro version, while what really matters
are the linker capabilties. gcc achieves that either through explicit configure
options, or if nothing is given, through autotools feature check tests. Why
does clang chooses to hardcode ldflags based on distro/distro versions ? How
are people having their own (coporate, so private) distro meant to configure
clang in that case ?
Cheers,
Romain
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