80 lines
4.3 KiB
Markdown
80 lines
4.3 KiB
Markdown
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## How to upgrade llvm_git
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- Run `update-git.py`.
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This will set the github revision and sha256 for `llvmPackages_git.llvm` to whatever the latest chromium build is using.
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For a more recent, commit run `nix-prefetch-github` and change the rev and sha256 accordingly.
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- That was the easy part.
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The hard part is updating the patch files.
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The general process is:
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1. Try to build `llvmPackages_git.llvm` and associated packages such as
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`clang` and `compiler-rt`. You can use the `-L` and `--keep-failed` flags to make
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debugging patch errors easy, e.g., `nix build .#llvmPackages_git.clang -L --keep-failed`
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2. The build will error out with something similar to this:
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```sh
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...
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clang-unstable> patching sources
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clang-unstable> applying patch /nix/store/nndv6gq6w608n197fndvv5my4a5zg2qi-purity.patch
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clang-unstable> patching file lib/Driver/ToolChains/Gnu.cpp
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clang-unstable> Hunk #1 FAILED at 487.
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clang-unstable> 1 out of 1 hunk FAILED -- saving rejects to file lib/Driver/ToolChains/Gnu.cpp.rej
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note: keeping build directory '/tmp/nix-build-clang-unstable-2022-25-07.drv-17'
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error: builder for '/nix/store/zwi123kpkyz52fy7p6v23azixd807r8c-clang-unstable-2022-25-07.drv' failed with exit code 1;
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last 8 log lines:
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> unpacking sources
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> unpacking source archive /nix/store/mrxadx11wv1ckjr2208qgxp472pmmg6g-clang-src-unstable-2022-25-07
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> source root is clang-src-unstable-2022-25-07/clang
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> patching sources
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> applying patch /nix/store/nndv6gq6w608n197fndvv5my4a5zg2qi-purity.patch
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> patching file lib/Driver/ToolChains/Gnu.cpp
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> Hunk #1 FAILED at 487.
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> 1 out of 1 hunk FAILED -- saving rejects to file lib/Driver/ToolChains/Gnu.cpp.rej
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For full logs, run 'nix log /nix/store/zwi123kpkyz52fy7p6v23azixd807r8c-clang-unstable-2022-25-07.drv'.
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note: keeping build directory '/tmp/nix-build-compiler-rt-libc-unstable-2022-25-07.drv-20'
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error: 1 dependencies of derivation '/nix/store/ndbbh3wrl0l39b22azf46f1n7zlqwmag-clang-wrapper-unstable-2022-25-07.drv' failed to build
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```
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Notice the `Hunk #1 Failed at 487` line.
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The lines above show us that the `purity.patch` failed on `lib/Driver/ToolChains/Gnu.cpp` when compiling `clang`.
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3. The task now is to cross reference the hunks in the purity patch with
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`lib/Driver/ToolCahins/Gnu.cpp.orig` to see why the patch failed.
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The `.orig` file will be in the build directory referenced in the line `note: keeping build directory ...`;
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this message results from the `--keep-failed` flag.
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4. Now you should be able to open whichever patch failed, and the `foo.orig` file that it failed on.
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Correct the patch by adapting it to the new code and be mindful of whitespace;
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which can be an easily missed reason for failures.
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For cases where the hunk is no longer needed you can simply remove it from the patch.
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This is fine for small corrections, but when more serious changes are needed its better to use git.
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1. Clone the LLVM monorepo at https://github.com/llvm/llvm-project/
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2. Check out the revision we were using before.
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3. Use `patch -p1 < path/to-path` in the project subdirectories to apply the patches and commit.
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4. Use `git rebase HEAD^ --onto <dest>` to rebase the patches onto the new revision we are trying to build, and fix all conflicts.
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5. Use `git diff HEAD^:<project> HEAD:<project>` to get subdir diff to write back to Nixpkgs.
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## Information on our current patch sets
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### "GNU Install Dirs" patches
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Use CMake's [`GNUInstallDirs`](https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html) to support multiple outputs.
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Previously, LLVM Just hard-coded `bin`, `include`, and `lib${LLVM_TARGET_PREFIX}`.
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We are making it use these variables.
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For the older LLVM versions, these patches live in https://github.com/Ericson2314/llvm-project branches `split-prefix`.
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Instead of applying the patches to the worktree per the above instructions, one can checkout those directly and rebase those instead.
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For newer LLVM versions, enough has has been upstreamed,
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(see https://reviews.llvm.org/differential/query/5UAfpj_9zHwY/ for my progress upstreaming),
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that I have just assembled new gnu-install-dirs patches from the remaining unmerged patches instead of rebasing from the prior LLVM's gnu install dirs patch.
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