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60 lines
2.5 KiB
Markdown
60 lines
2.5 KiB
Markdown
# Abseil BMI2 public header
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Vendored Abseil includes `bmi2intrin.h` directly when `__BMI2__` is enabled.
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Compilers reject that internal header without the umbrella-header setup.
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`bmi2-public-header.patch` includes `immintrin.h` instead, allowing builds
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that enable BMI2 through `-march=x86-64-v3`.
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## Scope and behavior
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The patch changes one include in
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`third_party/abseil-cpp/absl/container/internal/raw_hash_set.h`.
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`default.nix` applies it to Electron 43's unwrapped package, Deno's
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`librusty_v8`, and Signal's WebRTC dependency. It also supplies the patched
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Electron package to Signal. These overrides apply only to `x86-64-v3`.
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The shared file path is relative to each vendoring project's source root,
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not the root of a standalone Abseil checkout. No hash-table algorithm or
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test exclusion changes.
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## Reproduction and focused checks
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From this directory, check and apply the patch to each vendored source tree:
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```sh
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patch --dry-run --fuzz=0 -d /path/to/vendor-source -p1 < bmi2-public-header.patch
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patch --fuzz=0 -d /path/to/vendor-source -p1 < bmi2-public-header.patch
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```
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A small compiler check isolates the header requirement. With GCC or Clang
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on x86-64, compile `#include <bmi2intrin.h>` using `-march=x86-64-v3`; the
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compiler rejects the direct include. Changing it to `#include <immintrin.h>`
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should compile. The full consumer builds below check integration with their
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actual toolchains.
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## Upstream status
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Abseil addressed this issue through
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[PR #2071](https://github.com/abseil/abseil-cpp/pull/2071), imported by its
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upstream workflow. That change uses `x86gprintrin.h`; this local variant uses
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the public `immintrin.h` umbrella header for the vendored toolchains.
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Keep the workaround until all three bundled copies include a compatible fix.
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This file is a local adaptation, not a verbatim copy of the upstream diff.
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## Local NixOS integration and build results
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[`../default.nix`](../default.nix) merges this directory's overlay fragment
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because it repairs multiple packages. From the repository root, the consumer
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build commands are:
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```sh
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nix build --no-link -L .#nixosConfigurations.jeeves.pkgs.deno
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nix build --no-link -L .#nixosConfigurations.jeeves.pkgs.electron_43
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nix build --no-link -L .#nixosConfigurations.jeeves.pkgs.signal-desktop
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```
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The earlier extraction checked the vendored header snapshots and evaluated
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all three patch attachments. Those records do not establish successful full
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consumer rebuilds. No new compiler or consumer build was run for the layout
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change; the patch and override are unchanged.
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