#+TITLE: Gentoo LLVM_TARGETS not Working?
#+DATE: <2022-10-29 六>
#+OPTIONS: toc:nil

Recently, I would like to test switching from =gcc= to =clang= on my Gentoo VM.
Because if so, I can install =Rust= and =Zig= from source
without worrying about adding the HUGE =clang= dependency that won't be used by other packages.
Later I will remove =gcc= :)

* problem
First I want to make [[https://llvm.org][LLVM]] not targeting too many platform, but changing =LLVM_TARGETS= don't work
#+BEGIN_SRC shell
  [ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
  ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
  LLVM_TARGETS="(AArch64) (AMDGPU) (ARM) (AVR) (BPF) (Hexagon) (Lanai) (MSP430)
  (Mips) (NVPTX) (PowerPC) (RISCV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86)
  (XCore) (-ARC) (-CSKY) (-DirectX) (-LoongArch) (-M68k) (-SPIRV)" 241 KiB    
#+END_SRC

* and I found [[https://forums.gentoo.org/viewtopic.php?p=8694331][[solved] LLVM_TARGETS not respected?]](Mar 2022) on gentoo forum

It seems that global =LLVM_TARGETS= setting is not respected,
and flags such as =llvm_targets_AArch64=, =llvm_targets_ARM=, are no longer there.
They're now forced by default as a precaution.


* /*solution*/
** add something like =*/* -llvm_targets_AArch64= into =/etc/portage/profile/package.use.force=
I excluded all targets exept for X86, but still 3 left: AMDGPU, BPF, NVPTX
** so I also add =sys-devel/llvm -llvm_targets_AMDGPU -llvm_targets_BPF -llvm_targets_NVPTX= in =/etc/portage/package.use/=
** and don't forget to add that three excluder to clang or other compiler that uses llvm


* finally I got this:
#+BEGIN_SRC shell
  [ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
  ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
  LLVM_TARGETS="(X86) -AArch64 -AMDGPU (-ARC) -ARM -AVR -BPF (-CSKY) (-DirectX)
  -Hexagon -Lanai (-LoongArch) (-M68k) -MSP430 -Mips -NVPTX -PowerPC -RISCV
  (-SPIRV) -Sparc -SystemZ -VE -WebAssembly -XCore" 241 KiB
#+END_SRC

in the end, [[https://wiki.gentoo.org/wiki/Gentoo_Cheat_Sheet][Gentoo cheatsheet]] and [[https://wiki.gentoo.org/wiki/Clang][Gentoo Wiki: Clang]] could be useful.