Can't bootstrap 1.89 on Windows with custom dlltool

[jfgoog]

Summary

Bootstrapping rust 1.89.0 on Windows fails at "Building tool cargo (stage1 -> stage2, x86_64-pc-windows-gnu)" when using a custom dlltool.

Command used

Somewhat complicated to describe. We build a Rust toolchain for Android with a script that is a wrapper around x.py that creates a custom bootstrap.toml and sets some environment variables. Slightly out-of-date version of build scripts is at https://android.googlesource.com/toolchain/android_rust/+/refs/heads/main

Expected behaviour

• We are able to specify a custom dlltool that is used to bootstrap the toolchain.

Actual behaviour

• The build fails at "Building tool cargo (stage1 -> stage2, x86_64-pc-windows-gnu)"
• The failing command is C:/src/main-rust-toolchain/prebuilts/rust/windows-x86/1.88.0/bin/cargo.exe build --target x86_64-pc-windows-gnu -Zbinary-dep-depinfo -j 64 -Zroot-dir=C:\src\main-rust-toolchain\out\rustc -v --frozen --release --manifest-path C:\src\main-rust-toolchain\out\rustc\src/tools/cargo\Cargo.toml --features all-static
• The failing crate is getrandom 0.3.3, with the error "error: Error calling dlltool 'dlltool.exe': program not found"

We are specifying a custom dlltool in RUSTFLAGS with "-Cdlltool=XXXX". In practice, this doesn't actually work. There seem to be a number of things going on:

• Cargo ignores RUSTFLAGS when --target is set. This means that ALL of the rust flags, set by our build script and by the bootstrap process, are ignored, not just -Cdlltool=XXX
• When bootstrapping the new version of cargo, the bootstrap process uses the old (stage0) version of cargo, with the new version of rustc.
• But the bootstrap process needs to be able to pass some flags to rustc, such as telling rustc about the linker. It can't use RUSTFLAGS, so there is a special rustc wrapper (src/bootstrap/src/bin/rustc.rs) that, among other things, allows additional flags to be passed via RUSTC_HOST_FLAGS, which the bootstrap process sets before invoking cargo.
• In our case, RUSTC_HOST_FLAGS = "--check-cfg=cfg(bootstrap) -Ctarget-feature=-crt-static -Clinker=C:/src/main-rust-toolchain/out/wrappers/linker-x86_64-pc-windows-gnu.cmd"

This does not appear to be a new issue; it's probably been latent for awhile. It looks like what changed between rust 1.88 and 1.89 is the Cargo.lock file for cargo (src/tools/cargo/Cargo.lock) bumped the version of getrandom from 0.3.1 to 0.3.3, which changes the dependencies and compilation behavior on windows (see rust-random/getrandom#627 and rust-random/getrandom#723).

Bootstrap configuration (bootstrap.toml)

change-id = 131075

[llvm]
download-ci-llvm = false
ninja = true
targets = "AArch64;ARM;X86;RISCV"
link-shared = false
cflags = ""
cxxflags = ""
ldflags = "-Wl,-mllvm,--relocation-model=pic"
use-libcxx = true
static-libstdcpp = false
thin-lto = false
version-suffix = ""
libzstd = false


[llvm.build-config]
CMAKE_BUILD_RPATH = "C:/src/main-rust-toolchain/prebuilts/clang/host/windows-x86/clang-r574158/lib"


[build]
build = "x86_64-pc-windows-gnu"
host = ["x86_64-pc-windows-gnu"]
target = ["x86_64-pc-windows-gnu"]
cargo = "C:/src/main-rust-toolchain/prebuilts/rust/windows-x86/1.88.0/bin/cargo.exe"
rustc = "C:/src/main-rust-toolchain/prebuilts/rust/windows-x86/1.88.0/bin/rustc.exe"
python = "C:/src/main-rust-toolchain/prebuilts/python/windows-x86/python.exe"
verbose = 1
docs = false
submodules = false
vendor = true
full-bootstrap = true
extended = true
tools = ["cargo", "clippy", "rustdoc", "rustfmt", "rust-analyzer"]
cargo-native-static = true

[dist]
compression-formats = ["gz"]
include-mingw-linker = false

[install]
prefix = "/"
sysconfdir = "etc"

[rust]
channel = "dev"
description = "Android Rust Toolchain version windows"
download-rustc = false
remap-debuginfo = true
deny-warnings = false
new-symbol-mangling = true
lld = false
lto = "thin-local"


[target.x86_64-pc-windows-gnu]
cc = "C:/src/main-rust-toolchain/out/wrappers/clang-x86_64-pc-windows-gnu.cmd"
cxx = "C:/src/main-rust-toolchain/out/wrappers/clang++-x86_64-pc-windows-gnu.cmd"
linker = "C:/src/main-rust-toolchain/out/wrappers/linker-x86_64-pc-windows-gnu.cmd"
ar = "C:/src/main-rust-toolchain/prebuilts/clang/host/windows-x86/clang-r574158/bin/llvm-ar.exe"
ranlib = "C:/src/main-rust-toolchain/prebuilts/clang/host/windows-x86/clang-r574158/bin/llvm-ranlib.exe"
crt-static = false
llvm-libunwind = "in-tree"
profiler = false

Operating system

Windows 11

HEAD

2948388

With some patches: https://android.googlesource.com/toolchain/android_rust/+/refs/heads/main/patches/ (somewhat out-of-date due to AOSP turndown)

Additional context

Full set of environment variables used when invoking std::process::Command:

"AR_x86_64_pc_windows_gnu", Some("C:/src/main-rust-toolchain/prebuilts/clang/host/windows-x86/clang-r574158/bin/llvm-ar.exe")
"CARGO_INCREMENTAL", Some("0")
"CARGO_PROFILE_RELEASE_DEBUG", Some("0")
"CARGO_PROFILE_RELEASE_DEBUG_ASSERTIONS", Some("false")
"CARGO_PROFILE_RELEASE_OVERFLOW_CHECKS", Some("false")
"CARGO_PROFILE_RELEASE_STRIP", Some("false")
"CARGO_TARGET_DIR", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1-tools")
"CARGO_TARGET_X86_64_PC_WINDOWS_GNU_LINKER", Some("C:/src/main-rust-toolchain/out/wrappers/linker-x86_64-pc-windows-gnu.cmd")
"CC_x86_64_pc_windows_gnu", Some("C:/src/main-rust-toolchain/out/wrappers/clang-x86_64-pc-windows-gnu.cmd")
"CFG_COMMIT_DATE", Some("2025-06-23")
"CFG_COMMIT_HASH", Some("c24e1064277fe51ab72011e2612e556ac56addf7")
"CFG_COMPILER_BUILD_TRIPLE", Some("x86_64-pc-windows-gnu")
"CFG_COMPILER_HOST_TRIPLE", Some("x86_64-pc-windows-gnu")
"CFG_RELEASE", Some("1.89.0-dev")
"CFG_RELEASE_CHANNEL", Some("dev")
"CFG_RELEASE_NUM", Some("1.89.0")
"CFG_SHORT_COMMIT_HASH", Some("c24e10642")
"CFG_VERSION", Some("1.89.0-dev (29483883e 2025-08-04) (Android Rust Toolchain version windows)")
"CFG_VER_DATE", Some("2025-08-04")
"CFG_VER_DESCRIPTION", Some("Android Rust Toolchain version windows")
"CFG_VER_HASH", Some("29483883eed69d5fb4db01964cdf2af4d86e9cb2")
"CFLAGS_x86_64_pc_windows_gnu", Some("")
"CXXFLAGS_x86_64_pc_windows_gnu", Some("")
"CXX_x86_64_pc_windows_gnu", Some("C:/src/main-rust-toolchain/out/wrappers/clang++-x86_64-pc-windows-gnu.cmd")
"DOC_RUST_LANG_ORG_CHANNEL", Some("https://doc.rust-lang.org/nightly")
"LIBC_CHECK_CFG", Some("1")
"LIBZ_SYS_STATIC", Some("1")
"LZMA_API_STATIC", Some("1")
"MAKEFLAGS", None
"MFLAGS", None
"RANLIB_x86_64_pc_windows_gnu", Some("C:/src/main-rust-toolchain/prebuilts/clang/host/windows-x86/clang-r574158/bin/llvm-ar.exe s")
"REAL_LIBRARY_PATH", Some("C:\\src\\main-rust-toolchain\\prebuilts\\python\\windows-x86;C:\\src\\main-rust-toolchain\\prebuilts\\rust\\windows-x86\\1.88.0\\bin;C:\\src\\main-rust-toolchain\\prebuilts\\cmake\\windows-x86\\bin;C:\\src\\main-rust-toolchain\\prebuilts\\ninja\\windows-x86;C:\\src\\main-rust-toolchain\\prebuilts\\build-tools\\path\\windows-x86;C:\\src\\main-rust-toolchain\\prebuilts\\build-tools\\windows-x86\\bin;C:\\src\\main-rust-toolchain\\out\\rust-toolchain\\bin;C:\\program files\\git\\usr\\bin;C:\\src\\main-rust-toolchain\\prebuilts\\gcc\\linux-x86\\host\\x86_64-w64-mingw32-4.8\\x86_64-w64-mingw32\\bin;C:\\src\\main-rust-toolchain\\prebuilts\\gcc\\linux-x86\\host\\x86_64-w64-mingw32-4.8\\x86_64-w64-mingw32\\lib")
"REAL_LIBRARY_PATH_VAR", Some("PATH")
"RUSTBUILD_NATIVE_DIR", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\native")
"RUSTC", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\bootstrap\\debug\\rustc")
"RUSTC_BOOTSTRAP", Some("1")
"RUSTC_BREAK_ON_ICE", Some("1")
"RUSTC_CARGO_REGISTRY_SRC_TO_REMAP", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\vendor=/rust/deps")
"RUSTC_DEBUGINFO_MAP", Some("C:\\src\\main-rust-toolchain\\out\\rustc=/rustc/29483883eed69d5fb4db01964cdf2af4d86e9cb2")
"RUSTC_ERROR_METADATA_DST", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\tmp/extended-error-metadata")
"RUSTC_HOST_FLAGS", Some("--check-cfg=cfg(bootstrap) -Ctarget-feature=-crt-static -Clinker=C:/src/main-rust-toolchain/out/wrappers/linker-x86_64-pc-windows-gnu.cmd")
"RUSTC_INSTALL_BINDIR", Some("bin")
"RUSTC_LIBDIR", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1\\bin")
"RUSTC_LINK_STD_INTO_RUSTC_DRIVER", Some("0")
"RUSTC_LINT_FLAGS", Some("")
"RUSTC_REAL", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1\\bin\\rustc.exe")
"RUSTC_SNAPSHOT", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1\\bin\\rustc.exe")
"RUSTC_SNAPSHOT_LIBDIR", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1\\bin")
"RUSTC_STAGE", Some("1")
"RUSTC_SYSROOT", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1")
"RUSTC_TLS_MODEL_INITIAL_EXEC", Some("1")
"RUSTC_VERBOSE", Some("1")
"RUSTC_WRAPPER", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\bootstrap\\debug\\rustc")
"RUSTDOC", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\bootstrap\\debug\\rustdoc")
"RUSTDOCFLAGS", Some("-Crelocation-model=pic -Csave-temps -Cdlltool=C:\\src\\main-rust-toolchain\\prebuilts\\clang\\host\\windows-x86\\clang-r574158\\bin\\llvm-dlltool.exe --cfg=windows_raw_dylib -Csymbol-mangling-version=v0 -Zunstable-options --check-cfg=cfg(bootstrap) --check-cfg=cfg(llvm_enzyme) --check-cfg=cfg(rust_analyzer) -Clinker=C:\\src\\main-rust-toolchain\\out\\wrappers\\linker-x86_64-pc-windows-gnu.cmd --crate-version 1.89.0-dev\t(29483883e\t2025-08-04)\t(Android\tRust\tToolchain\tversion\twindows) -Clinker=C:/src/main-rust-toolchain/out/wrappers/linker-x86_64-pc-windows-gnu.cmd")
"RUSTDOC_REAL", Some("/path/to/nowhere/rustdoc/not/required")
"RUSTFLAGS", Some("-Crelocation-model=pic -Csave-temps -Cdlltool=C:\\src\\main-rust-toolchain\\prebuilts\\clang\\host\\windows-x86\\clang-r574158\\bin\\llvm-dlltool.exe --cfg=windows_raw_dylib -Csymbol-mangling-version=v0 -Zunstable-options --check-cfg=cfg(bootstrap) --check-cfg=cfg(llvm_enzyme) --check-cfg=cfg(rust_analyzer) -Zmacro-backtrace -Csplit-debuginfo=packed -Ctarget-feature=-crt-static -Clink-arg=-LC:/src/main-rust-toolchain/out/rustc/build/x86_64-pc-windows-gnu/llvm/lib -Alinker-messages -Zunstable-options")
"RUST_TEST_THREADS", Some("64")
"SYSROOT", Some("C:\\src\\main-rust-toolchain\\out\\rustc\\build\\x86_64-pc-windows-gnu\\stage1")
"__CARGO_DEFAULT_LIB_METADATA", Some("devtool-rustc1.89.0")

[jfgoog]

It looks like MAGIC_EXTRA_RUSTFLAGS might do the trick.

[Urgau]

We may want to add proper support for setting -Cdlltool from bootstrap.toml, similar to what we did for windows-rc in #146663 with a [build] dlltool = "/path/to/dlltool".

[jfgoog]

I agree that it would be nice to be able to set this in bootstrap.toml.

[jieyouxu]

cc #103939

[mati865]

We may want to add proper support for setting -Cdlltool from bootstrap.toml, similar to what we did for windows-rc in #146663 with a [build] dlltool = "/path/to/dlltool".

Or getting rid of dlltool entirely.

[jfgoog]

I can probably figure out how to add dlltool to bootstrap.toml, using the windows-rc code as an example.

I don't know how to eliminate use of dlltool completely, but I'm definitely willing to try, if I can get some guidance.

Let me know if you'd like me to pursue either of these options.

(In the meantime, MAGIC_EXTRA_RUSTFLAGS did the trick.)

[mati865]

I don't know how to eliminate use of dlltool completely, but I'm definitely willing to try, if I can get some guidance.

The change itself is super-easy, basically delete

rust/compiler/rustc_codegen_ssa/src/back/archive.rs

Line 85 in 4b9c62b

if common::is_mingw_gnu_toolchain(&sess.target) {

and all the now dead code.
The hard part is assessing whether it's find to do that change. Binutils <2.40 breaks when it has to link library with embedded short import lib (like the one made by LLVM), the versions that Rust supports are not declared or even decided. So, somebody needs to work out the supported external tools versions first.

[jfgoog]

We build the Android toolchain with Clang/LLVM, and that's where our dlltool comes from.

Are you fairly certain that newer versions of binutils (>= 2.40) will work, or just that older versions don't? It looks like binutils 2.40 was released in 2023, which is fairly recent.

Is it documented anywhere which external tools are supported?

What would be required to test the change? Build a toolchain with various versions of binutils and llvm? That seems like it would be fairly labor-intensive.

[mati865]

We build the Android toolchain with Clang/LLVM, and that's where our dlltool comes from.

You might have more luck with windows-gnullvm host, then. Full disclosure: I maintain windows-gnullvm targets.

Are you fairly certain that newer versions of binutils (>= 2.40) will work, or just that older versions don't?

Good question!
There were/are multiple bugs regarding import libs in Binutils, at least one or two significant ones were fixed in 2.40. I take no responsibility for declaring which versions are fully fixed (if any).

It looks like binutils 2.40 was released in 2023, which is fairly recent.

Yeah, for example, Ubuntu 22.04 ships 2.38.

Is it documented anywhere which external tools are supported?

That's one part of the hard task, there is no documentation in this matter whatsoever.

What would be required to test the change? Build a toolchain with various versions of binutils and llvm? That seems like it would be fairly labor-intensive.

TBH I am not certain, but probably building the toolchain with the change and test creating cdylib type crates using various popular mingw-w64 based toolchains.