x.py build --stage 1 src/rustc --host=$HOST cross compiles rustc two times

[japaric]

(In this example BUILD = x86_64-unknown-linux-gnu and HOST=arm-unknown-linux-gnueabi)

$ x.py build --stage 1 src/rustc --host=$HOST
Building stage0 std artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
(..)
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
(..)
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
(..)
Building stage1 std artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage1 test artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage1 compiler artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)

This part:

Building stage0 std artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage0 test artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)
Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
(..)

seems unnecessary as that compiler won't be used in the bootstrap (in fact, it can be executed by the build machine due to the differences in architectures) and it's not the requested rustc either.

cc @alexcrichton

[japaric]

Also it seems the wrong rustc is being copied into the output directory:

$ diff -u \
    ./build/arm-unknown-linux-gnueabi/stage1/bin/rustc \
    ./build/x86_64-unknown-linux-gnu/stage0-rustc/arm-unknown-linux-gnueabi/release/rustc && \
    echo SAME
SAME

$ diff -u \
    ./build/arm-unknown-linux-gnueabi/stage1/bin/rustc \
    ./build/x86_64-unknown-linux-gnu/stage1-rustc/arm-unknown-linux-gnueabi/release/rustc && \
    echo SAME
Binary files ./build/arm-unknown-linux-gnueabi/stage1/bin/rustc and ./build/x86_64-unknown-linux-gnu/stage1-rustc/arm-unknown-linux-gnueabi/release/rustc differ

build/$HOST/stage1/bin/rustc should be build/$BUILD/stage1-rustc/$HOST/release/rustc not stage0-rustc, right?

[alexcrichton]

Hm ok some of this is expected, some of this isn't expected. I can't seem to quite make sense of your original logs, though. Are you sure that x.py build --stage 1 src/rustc --host=$HOST was executed exactly to produce that trace? I unfortunately can't seem to reconstruct the sequence of events on master that'd lead to that.

[japaric]

@alexcrichton repro as a shell script

# Ubuntu 16.04
# SRC_DIR is the rust-lang/rust source

main() {
    ARCH=armel
    BUILD=x86_64-unknown-linux-gnu
    HOST=arm-unknown-linux-gnueabi
    PREFIX=arm-linux-gnueabi

   sudo apt-get install -y --no-install-recommends \
        g++-$PREFIX libc6-dev-$ARCH-cross

   $SRC_DIR/configure \
       --enable-ccache \
       --enable-ninja \
       --enable-rustbuild \
       --host=$HOST

   # work around rust-lang/rust#38037
   nice $SRC_DIR/x.py build --stage 1 src/llvm --host=$BUILD

   # STDOUT
   # Building LLVM for x86_64-unknown-linux-gnu

   nice $SRC_DIR/x.py build --stage 1 src/rustc --host=$HOST

   # STDOUT
   # Building stage0 std artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
   # Building stage0 test artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
   # Building LLVM for arm-unknown-linux-gnueabi
   # Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
   # Building stage0 std artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   # Building stage0 test artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   # Building stage0 compiler artifacts (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
   # Building stage1 std artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
   # Building stage1 test artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
   # Building stage1 compiler artifacts (x86_64-unknown-linux-gnu -> arm-unknown-linux-gnueabi)
}

main

Meta

$ git rev-parse HEAD
0b399e5e99a44cf44d3860d353a8b7619d466410

[alexcrichton]

Ok addressed in #38076 (this path redirected to the wrong step) but it'll need #37817 as well to be maximally effective.