On Thu, Oct 28, 2021 at 10:44:06AM -0700, Nathan Chancellor wrote: > I like the first iteration of this idea most, as CC=clang does not > currently imply using all LLVM tools. There are some architectures that > work with CC=clang but not LLVM=1 so I am not sure we want that meaning > to change. Could such architecture set a CONFIG symbol to indicate they're handicapped and have that make the Makefile not use the full LLVM suite? > I do think this issue of Debian's different clang versions needs to be > resolved as more and more LLVM features are being developed and non-LLVM > or ClangBuiltLinux developers want to test these features and make sure > that they work properly. There are a few different options: > > 1. Take Peter's first patch so that LLVM=1 and LLVM=-# can be used. The > documentation should be updated to convey this change. The argument > against doing this might be that Debian/Ubuntu/derivatives of either > are special for using versioned suffixes and we do not want to add > this to the build system but I think that might be short sighted. > Peter's patch is not super complex nor does it change the status quo > of LLVM=1. Also, I *greatly* appreciate having multiple versions of the compiler at hand. I really think debian does the right thing here and other distros are at a disadvantage. Note: also Segher's buildall script generates version suffixed GCC builds. > 2. Update the documentation to describe using the > > $ PATH=/usr/lib/llvm-#/bin:$PATH make LLVM=1 ... > > trick. This has been the preferred method for using different > versions of LLVM but it has never been documented anywhere. This > would allow us to keep the current build infrastructure while giving > people clear instructions for how to handle different versions of > clang. As Peter has noted, this would require people who are not > familiar with building with LLVM to be constantly looking at the > documentation to remember the command to invoke, whereas with > LLVM=-#, it is easy to remember. Right, this is no more than a crude hack and is super unfriendly. It should never have been accepted. > 3. Explore recommending update-alternatives in the documentation or > working with Debian to provide this automatically. As this is a > Debian and derivatives only problem, a solution for it could come > from the distribution itself. I found one post from a few years ago > that talks about this but a command to use all LLVM tools from a > particular version would be rather unweildy: > > https://askubuntu.com/questions/791616/set-clang-3-8-as-default I also don't really appreciate this, I don't want to change the system default 'clang' just to build a kernel. I might build the kernel with various different compilers consecutively to look at differences in code gen for example. Why should I not be able to build them concurrently? > Overall, I think I like #1 the best. It is not that much more > complicated than what we have now and it leaves it entirely up to the > user how they want to build and it is hard for them to shoot themselves > in the foot. I am open to other suggestions or arguments though :) So I've been doing kernel builds using: $ make O=foo CC=gcc-$ver for *years*, and I really don't understand or appreciate why building a clang kernel needs to be so damn difficult. The whole: LLVM=1 thing is just wrong. $ make O=foo CC=clang-$ver *should* just work. This not working is a pain bug; people peddling crazy things like 2) above is just mind-boggling insane. Having a document explaining how to do an LLVM build should be a clue it's wrong. So how about we do the below instead? Then the normal way of things will be: $ make CC=clang-12 and it will all *just*work*. The incomplete LLVM archs can revert back to the old hybrid (clang+binutils) way of things by doing: $ make CC=clang LLVM=0 Which explicitly states, use clang but don't use the full llvm suite. Or they can do that CONFIG_LLVM_BROKEN (or whatever) to have them default to LLVM=0 ifdef CONFIG_LLVM_BROKEN LLVM ?= 0 endif in front of the CC magic in the below patch should take care of that. (also, having all this gunk twice isn't useful) --- Makefile | 26 ++++++++++++++++---------- tools/scripts/Makefile.include | 22 ++++++++++++++-------- 2 files changed, 30 insertions(+), 18 deletions(-) --- a/Makefile +++ b/Makefile @@ -423,9 +423,15 @@ HOST_LFS_CFLAGS := $(shell getconf LFS_C HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null) HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null) +CC_BASE = $(shell echo $(CC) | cut -b "1-5") +ifeq ($(shell test "$(CC_BASE)" = "clang"; echo $$?),0) +LLVM ?= 1 +LLVM_SFX := $(shell echo $(CC) | cut -b "6-") +endif + ifneq ($(LLVM),) -HOSTCC = clang -HOSTCXX = clang++ +HOSTCC = clang$(LLVM_SFX) +HOSTCXX = clang++$(LLVM_SFX) else HOSTCC = gcc HOSTCXX = g++ @@ -443,14 +449,14 @@ KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) # Make variables (CC, etc...) CPP = $(CC) -E ifneq ($(LLVM),) -CC = clang -LD = ld.lld -AR = llvm-ar -NM = llvm-nm -OBJCOPY = llvm-objcopy -OBJDUMP = llvm-objdump -READELF = llvm-readelf -STRIP = llvm-strip +CC = clang$(LLVM_SFX) +LD = ld.lld$(LLVM_SFX) +AR = llvm-ar$(LLVM_SFX) +NM = llvm-nm$(LLVM_SFX) +OBJCOPY = llvm-objcopy$(LLVM_SFX) +OBJDUMP = llvm-objdump$(LLVM_SFX) +READELF = llvm-readelf$(LLVM_SFX) +STRIP = llvm-strip$(LLVM_SFX) else CC = $(CROSS_COMPILE)gcc LD = $(CROSS_COMPILE)ld --- a/tools/scripts/Makefile.include +++ b/tools/scripts/Makefile.include @@ -51,12 +51,18 @@ define allow-override $(eval $(1) = $(2))) endef +CC_BASE = $(shell echo $(CC) | cut -b "1-5") +ifeq ($(shell test "$(CC_BASE)" = "clang"; echo $$?),0) +LLVM ?= 1 +LLVM_SFX := $(shell echo $(CC) | cut -b "6-") +endif + ifneq ($(LLVM),) -$(call allow-override,CC,clang) -$(call allow-override,AR,llvm-ar) -$(call allow-override,LD,ld.lld) -$(call allow-override,CXX,clang++) -$(call allow-override,STRIP,llvm-strip) +$(call allow-override,CC,clang$(LLVM_SFX)) +$(call allow-override,AR,llvm-ar$(LLVM_SFX)) +$(call allow-override,LD,ld.lld$(LLVM_SFX)) +$(call allow-override,CXX,clang++$(LLVM_SFX)) +$(call allow-override,STRIP,llvm-strip$(LLVM_SFX)) else # Allow setting various cross-compile vars or setting CROSS_COMPILE as a prefix. $(call allow-override,CC,$(CROSS_COMPILE)gcc) @@ -69,9 +75,9 @@ endif CC_NO_CLANG := $(shell $(CC) -dM -E -x c /dev/null | grep -Fq "__clang__"; echo $$?) ifneq ($(LLVM),) -HOSTAR ?= llvm-ar -HOSTCC ?= clang -HOSTLD ?= ld.lld +HOSTAR ?= llvm-ar$(LLVM_SFX) +HOSTCC ?= clang$(LLVM_SFX) +HOSTLD ?= ld.lld$(LLVM_SFX) else HOSTAR ?= ar HOSTCC ?= gcc
