build: replace mold with the wild linker

.cargo/config.toml

@@ -1,16 +1,16 @@
-# Use a linker wrapper that invokes mold then strips junk sections with objcopy.
-# mold cannot discard .eh_frame/.dynstr/.comment via linker scripts, so we do
-# it as a post-link step.
-# See:
-#  <https://github.com/rui314/mold?tab=readme-ov-file#how-to-use>
+# Link the tier-1 Linux arches with the wild linker, driven by clang via the
+# scripts/clang-wild wrapper.
 #
 # Binary-specific link flags live in microfetch/build.rs via cargo:rustc-link-arg-bin
 # so they only affect the final binary and don't break proc-macro or build-script linking.
 [target.'cfg(target_os = "linux")']
-linker = "scripts/ld-wrapper"
-rustflags = [
-  # Suppress .eh_frame emission from our own codegen (does not cover compiler_builtins;
-  # those remnants are removed by the linker wrapper via objcopy post-link)
-  "-C",
-  "force-unwind-tables=no",
-]
+# Suppress .eh_frame emission from our own codegen.
+rustflags = ["-C", "force-unwind-tables=no"]
+
+[target.x86_64-unknown-linux-gnu]
+linker = "scripts/clang-wild"
+rustflags = ["-C", "force-unwind-tables=no"]
+
+[target.aarch64-unknown-linux-gnu]
+linker = "scripts/clang-wild"
+rustflags = ["-C", "force-unwind-tables=no"]

.github/workflows/hotpath-profile.yml

@@ -19,8 +19,10 @@ jobs:
         with:
           rustflags: ""
 
-      - name: Make Mold the default linker
-        uses: rui314/setup-mold@v1
+      - name: Install the wild linker
+        uses: wild-linker/action@0.9.0
+      - name: Put wild on PATH
+        run: echo "$RUNNER_TEMP/wild-install" >> "$GITHUB_PATH"
 
       - name: Create metrics directory
         run: mkdir -p /tmp/metrics

.github/workflows/rust.yml

@@ -73,8 +73,10 @@ jobs:
       if: ${{ !matrix.build_std }}
       run: rustup target add ${{ matrix.target }}
 
-    - name: "Make Mold the default linker"
-      uses: rui314/setup-mold@v1
+    - name: "Install the wild linker"
+      uses: wild-linker/action@0.9.0
+    - name: "Put wild on PATH"
+      run: echo "$RUNNER_TEMP/wild-install" >> "$GITHUB_PATH"
 
     - name: "Setup cross-compilation toolchain"
       uses: taiki-e/setup-cross-toolchain-action@v1

docs/README.md

@@ -59,7 +59,8 @@ welcome to use it on your system: it is pretty _[fast](#benchmarks)_...
 - Respects [`NO_COLOR` spec](https://no-color.org/)
 - Funny [^1]
 
-[^1]: I don't know how else to describe the (unhealthy) amount of handwritten
+[^1]:
+    I don't know how else to describe the (unhealthy) amount of handwritten
     assembly that was written in order to make Microfetch faster.
 
 ## Motivation
@@ -234,7 +235,7 @@ interested in Microfetch tailored to their distributions.
 
 ## Customizing
 
-You can't*
+You can't\*
 
 ### Really?
 
@@ -302,17 +303,19 @@ A Nix flake is provided. You may use `nix develop` to get started. Direnv users
 may instead run `direnv allow` to get a complete environment with shell
 integration.
 
-Non-Nix user will need `cargo`, `clang` and `mold` installed on their system to
-build Microfetch. As Mold seems to yield _slightly_ better results than the
-default linker, it has been set as the default in `.cargo/config.toml` for
-x86-64 Linux. You may override those defaults using the `RUSTFLAGS` environment
-variable. For example:
+Non-Nix users will need `cargo`, `clang` and [`wild`] on their `PATH` to build
+Microfetch. `wild` is faster than the default linker and emits a tighter binary,
+so it is set as the linker (via `clang`) in `.cargo/config.toml` for x86-64 and
+aarch64 Linux. To use a different linker, override it with the `RUSTFLAGS`
+environment variable. For example:
 
 ```sh
-# Use ld instead of Mold
+# Use ld instead of wild
 $ RUSTFLAGS="-C linker=/path/to/ld.lld" cargo build
 ```
 
+[`wild`]: https://github.com/wild-linker/wild
+
 ## Thanks
 
 Huge thanks to everyone who took the time to make pull requests or nag me in

nix/package.nix

@@ -2,12 +2,20 @@
   lib,
   rustPlatform,
   llvm,
+  clang,
+  wild,
 }: let
   pname = "microfetch";
   toml = (lib.importTOML ../Cargo.toml).workspace.package;
   inherit (toml) version;
+  inherit (llvm) stdenv;
+
+  # wild + clang are only used on Linux tier-1 arches
+  hasWild =
+    stdenv.hostPlatform.isLinux
+    && (stdenv.hostPlatform.isx86_64 || stdenv.hostPlatform.isAarch64);
 in
-  rustPlatform.buildRustPackage.override {inherit (llvm) stdenv;} (finalAttrs: {
+  rustPlatform.buildRustPackage.override {inherit stdenv;} (finalAttrs: {
     __structuredAttrs = true;
 
     inherit pname version;
@@ -21,12 +29,17 @@ in
           (s + /.cargo)
           (s + /crates)
           (s + /microfetch)
-          (s + /scripts/ld-wrapper)
           (s + /Cargo.lock)
           (s + /Cargo.toml)
         ];
       };
 
+    nativeBuildInputs = lib.optionals hasWild [wild clang];
+
+    env = lib.optionalAttrs hasWild {
+      RUSTFLAGS = "-Cforce-unwind-tables=no -Clinker=${clang}/bin/clang -Clink-arg=--ld-path=${wild}/bin/wild";
+    };
+
     cargoLock.lockFile = "${finalAttrs.src}/Cargo.lock";
     enableParallelBuilding = true;
     buildNoDefaultFeatures = true;

nix/shell.nix

@@ -2,7 +2,7 @@
   mkShell,
   cargo,
   rustc,
-  mold,
+  wild,
   clang,
   rust-analyzer,
   rustfmt,
@@ -16,7 +16,7 @@ mkShell {
   nativeBuildInputs = [
     cargo
     rustc
-    mold
+    wild
     clang
 
     rust-analyzer

scripts/clang-wild

@@ -0,0 +1,5 @@
+#!/usr/bin/env sh
+# Link via clang+wild. Wild sits behind the linker (not a rustflag) so a
+# cross-toolchain that overrides the linker drops it instead of choking on
+# --ld-path. Needs clang and wild on PATH.
+exec clang --ld-path=wild "$@"

scripts/ld-wrapper

@@ -1,38 +0,0 @@
-#!/usr/bin/env sh
-# Invoke mold, then strip junk sections from the output binary with objcopy.
-# This (more or less) removes sections that mold cannot discard itself, such as:
-#  - .eh_frame / .eh_frame_hdr  - unwind tables from compiler_builtins
-#  - .dynstr                     - mold emits this, even for fully static binaries
-#  - .comment                   - compiler version string
-#
-#  We forward everything to mold via -fuse-ld, then post-process the output in place.
-
-set -eu
-
-# Locate the output file and detect static linking
-IS_STATIC=0
-OUTPUT=""
-prev=""
-for arg in "$@"; do
-	case "$arg" in
-		-static) IS_STATIC=1 ;;
-	esac
-	if [ "$prev" = "-o" ]; then
-		OUTPUT="$arg"
-	fi
-	prev="$arg"
-done
-
-# Invoke mold via the cc driver, forward all original arguments
-cc -fuse-ld=mold "$@"
-
-# Only strip sections from fully static binaries.
-# Dynamic executables (i.e. build scripts, proc-macros) need .dynstr at runtime.
-if [ "$IS_STATIC" = 1 ] && [ -n "$OUTPUT" ] && [ -f "$OUTPUT" ]; then
-	objcopy \
-		--remove-section=.eh_frame \
-		--remove-section=.eh_frame_hdr \
-		--remove-section=.dynstr \
-		--remove-section=.comment \
-		"$OUTPUT"
-fi