std not found when trying to cross-compile tools

[infinity0]

We are adding rustfmt and clippy to the Debian package. Previously, with just rustc without these tools, cross-compiling works fine. When adding tools however, the cross-compile of these tools fails.

For example cross-compiling from x86_64 to armv5te:

[..]
        < Rustc { target: TargetSelection { triple: "armv5te-unknown-linux-gnueabi", file: None }, compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Libdir { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }, target: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } }
        c Sysroot { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Sysroot { compiler: Compiler { stage: 2, host: TargetSelection { triple: "x86_64-unknown-linux-gnu", file: None } } }
        c Llvm { target: TargetSelection { triple: "armv5te-unknown-linux-gnueabi", file: None } }
Building stage2 tool rustfmt (armv5te-unknown-linux-gnueabi)
running: "/usr/bin/cargo" "build" "--target" "armv5te-unknown-linux-gnueabi" "-Zdual-proc-macros" "-Zbinary-dep-depinfo" "-j" "4" "-v" "-v" "--release" "--manifest-path" "/<<PKGBUILDDIR>>/src/tools/rustfmt/Cargo.toml" "--message-format" "json-render-diagnostics"
   Compiling proc-macro2 v1.0.24
     Running `CARGO=/usr/bin/cargo CARGO_CRATE_NAME=build_script_build CARGO_MANIFEST_DIR=/<<PKGBUILDDIR>>/vendor/proc-macro2 CARGO_PKG_AUTHORS='Alex Crichton <alex@alexcrichton.com>:David Tolnay <dtolnay@gmail.com>' CARGO_PKG_DESCRIPTION='A substitute implementation of the compiler'\''s `proc_macro` API to decouple
token-based libraries from the procedural macro use case.
' CARGO_PKG_HOMEPAGE='' CARGO_PKG_LICENSE='MIT OR Apache-2.0' CARGO_PKG_LICENSE_FILE='' CARGO_PKG_NAME=proc-macro2 CARGO_PKG_REPOSITORY='https://github.com/alexcrichton/proc-macro2' CARGO_PKG_VERSION=1.0.24 CARGO_PKG_VERSION_MAJOR=1 CARGO_PKG_VERSION_MINOR=0 CARGO_PKG_VERSION_PATCH=24 CARGO_PKG_VERSION_PRE='' LD_LIBRARY_PATH='/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2-tools/release/deps:/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2/lib' /<<PKGBUILDDIR>>/build/bootstrap/debug/rustc --crate-name build_script_build --edition=2018 /<<PKGBUILDDIR>>/vendor/proc-macro2/build.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type bin --emit=dep-info,link -C opt-level=3 -Cembed-bitcode=no -C debuginfo=2 --cfg 'feature="default"' --cfg 'feature="proc-macro"' -C metadata=513cd11018457a4d -C extra-filename=-513cd11018457a4d --out-dir /<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2-tools/release/build/proc-macro2-513cd11018457a4d -L dependency=/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2-tools/release/deps --cap-lints warn -Zbinary-dep-depinfo`
[..]
error[E0463]: can't find crate for `std`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error[E0463]: can't find crate for `std`


Did not run successfully: exit code: 1
"/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--crate-name" "build_script_build" "--edition=2018" "/<<PKGBUILDDIR>>/vendor/proc-macro2/build.rs" "--error-format=json" "--json=diagnostic-rendered-ansi" "--crate-type" "bin" "--emit=dep-info,link" "-C" "opt-level=3" "-Cembed-bitcode=no" "-C" "debuginfo=2" "--cfg" "feature=\"default\"" "--cfg" "feature=\"proc-macro\"" "-C" "metadata=513cd11018457a4d" "-C" "extra-filename=-513cd11018457a4d" "--out-dir" "/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2-tools/release/build/proc-macro2-513cd11018457a4d" "-L" "dependency=/<<PKGBUILDDIR>>/build/x86_64-unknown-linux-gnu/stage2-tools/release/deps" "--cap-lints" "warn" "-Zbinary-dep-depinfo" "-Clinker=x86_64-linux-gnu-gcc" "--remap-path-prefix" "/<<PKGBUILDDIR>>=/usr/src/rustc-1.52.1"

[infinity0]

std is actually already built for the target architecture, the build still fails if i build it explicitly beforehand. It would seem that the correct paths are not being passed to the cross-compile of the tool.

[infinity0]

It's a bit weird that bootstrap says running: "/usr/bin/cargo" "build" "--target" "armv5te-unknown-linux-gnueabi" [..] but the cargo verbose output doesn't mention armv5te anywhere and only contains x86_64 paths.

[infinity0]

Oh, probably cargo is trying to build the dependencies of the build-scripts on the host platform, that's why --target is not being given. I am testing this diff:

diff --git a/src/bootstrap/tool.rs b/src/bootstrap/tool.rs
index 3fc3b68fd..2622b0785 100644
--- a/src/bootstrap/tool.rs
+++ b/src/bootstrap/tool.rs
@@ -52,7 +52,10 @@ impl Step for ToolBuild {
         let is_optional_tool = self.is_optional_tool;
 
         match self.mode {
-            Mode::ToolRustc => builder.ensure(compile::Rustc { compiler, target }),
+            Mode::ToolRustc => {
+                builder.ensure(compile::Std { compiler, target: compiler.host });
+                builder.ensure(compile::Rustc { compiler, target });
+            },
             Mode::ToolStd => builder.ensure(compile::Std { compiler, target }),
             Mode::ToolBootstrap => {} // uses downloaded stage0 compiler libs
             _ => panic!("unexpected Mode for tool build"),

to see if it fixes the problem.