On Sun, Oct 31, 2021 at 02:18:01AM +0100, Sedat Dilek wrote: > On Sat, Oct 30, 2021 at 4:34 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > > Latestest greatness... :-) > > > > --- > > Subject: kbuild: Fix clang/llvm build infra > > > > Debian (and derived) distros ship their compilers as -$ver suffixed > > binaries. For gcc it is sufficent to use: > > > > $ make CC=gcc-12 > > > > However, clang builds (esp. clang-lto) need a whole array of tools to be > > exactly right, leading to unweildy stuff like: > > > > $ make CC=clang-13 LD=ld.lld=14 AR=llvm-ar-13 NM=llvm-nm-13 OBJCOPY=llvm-objcopy-13 OBJDUMP=llvm-objdump-13 READELF=llvm-readelf-13 STRIP=llvm-strip-13 LLVM=1 > > > > which is, quite franktly, totally insane and unusable. Instead make > > the CC variable DTRT, enabling one such as myself to use: > > > > $ make CC=clang-13 > > > > This also lets one quickly test different clang versions. > > Additionally, also support path based LLVM suites like: > > > > $ make CC=/opt/llvm/bin/clang > > > > Hi Peter, > > Thanks for bringing this up again. > > Your issue is not new for Debianist and Linux-LLVM/Clang folks. > > But let me comment. > > I agree, it is preferable or should be treated the same way in using > clang-$ver like gcc-$ver. > > Background: Right, I know that. > As a compromise I use in my build_linux-llvm-toolchain.sh script > But... > > ...for several new features like Clang-LTO we need the LLVM full "eco system". > LLVM eco system means compiler, linker and binutils. > In several talks at LPC 2021 talkers used the term "LLVM/binutils" > like for GNU/binutils. > The LLVM/Clang kernel-docs talk about "LLVM util(itie)s" which is set > by LLVM=1 or not (LLVM=0). > > Link: https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities > > AFAICS your patch has a primary focus to fix the LLVM/Clang > infrastructure when CONFIG_LTO_CLANG=y, right? > Can you massage the commit message to reflect this? It already does :-) Also, it's a little bit more complicated, you can't actually select CONFIG_LTO *unless* you've configured your toolchain just right. > IMHO your patch can be improved to check for CONFIG_LTO_CLANG=y where > LLVM=1 is mandatory and IIRC LLVM_IAS=1, too. > ( The default to use LLVM/Clang-IAS (Integrated ASsembler) was changed > recently for some combinations arches + Clang-LTO? ) Egg, meet chicken :-) > Before I forgot: > Can you add a comment for the PPC and S390 situation in the commit message. Sure. > Please remember people also want to use combinations like gcc-$ver and > LLVM/binutils like ld.lld-$ver. make CC=gcc LLVM=1 make CC=clang LLVM=0 are still valid combinations that work, I just don't think they ought to be the default. > GCC-10 + LLD-$VER was the fastest combination to build a Linux Debian > package here on my Intel SandyBridge CPU system. > ( There exists overrides like LD=... STRIP=... and I use > XXX_FOR_BUILD=... (see my attached build-script). ) Right, that's what overrides are for, non-default setups. I just, quite strongly, feel that our defaults are completely insane. ~ Peter
