Re: [gentoo-soc] Weekly Report: Portage Powered Android

[Gunwant Jain <therealgunwant@gmail.com>]

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On 20/07/25 11:00AM, Benda Xu wrote:
> Gunwant Jain <therealgunwant@gmail.com> writes:
> 
> > Yes it did.
> > I can also report that llvm_android's stage1 clang is compiled for
> > aarch64, I am on the stage2 step currently.
> 
> Good.  Could you please remind me of the meanings of llvm stage1 and
> stage2?

Sure. AOSP provides its own distribution of LLVM. So most of what stage1
and stage2 I will be describing could be taken from [1]. 
Basically, we build LLVM stage1 using our own host toolchain. Then we
use the newly built stage1 compiler to build stage2, the ready to use
toolchain.

Coming to how this goes in our use-case, if we were to build the LLVM
toolchain using llvm_android (basically just build scripts), we will use
a prebuilt Clang toolchain, bundled with llvm_android to build stage1. 
Also AOSP targets only X86 architechture in stage1.
After stage1 is built, the build script proceeds to start building
stage2. This is where we use the newly built stage1 compilers to build
stage2 compilers. AOSP targets AArch64, ARM, X86 and BPF when building
stage2. Then the build script packages stage2 install and dumps the tar
for our use.

In the cycle of AOSP development, this newly packaged stage2 will be
provided as the prebuilt LLVM toolchain in [2]. This repository is used:
    - In the AOSP tree, when someone builds a new custom ROM.
    - In llvm_android as the prebuilt toolchain used to build a version
      bumped stage1.

For us, we will have to target AArch64 in building both stage1 and
stage2.


Regards,
Gunwant

[1] https://llvm.org/docs/BuildingADistribution.html
[2] https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/

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