rust-native & rust-cross: "error: multiple dylib candidates for `std` found"

[codyps]

Need to be more careful about how we tell rustc's build process to search for libraries to link against, in particular we need to convince it not to search ${libdir} when doing the initial builds.

The problem there is the search of ${libdir} is:

• necessary to find rust-llvm
• is also part of our generated target.json (so invocations of the final rustc to build other things look in ${libdir}).

[codyps]

CFG_LLVM_LINKAGE_FILE=/home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/build/x86_64-linux/rt/llvmdeps.rs LD_LIBRARY_PATH=/home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi:$LD_LIBRARY_PATH   x86_64-linux/stage0/bin/rustc --cfg stage0  -O --cfg rtopt --cfg ndebug -g -C rpath -C prefer-dynamic -Z no-landing-pads --target=x86_64-linux --sysroot "x86_64-linux/stage0" -L "x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib"  -W warnings -L "x86_64-linux/rt" -L "/home/buildbot_slave/buildbot/yocto-basic/obj/tmp/sysroots/x86_64-linux/usr/lib"   --out-dir x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib -C extra-filename=-e9599659 /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/librustc_llvm/lib.rs
| info: now are following matches for libstd-*.so libraries:
| x86_64-linux/stage1/lib/arm-poky-linux-gnueabi/libstd-e9599659.so
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                            ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1:1: 1:1 note: candidate #1: /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-e9599659.so
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                            ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1:1: 1:1 note: candidate #2: /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-e9599659.so
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                            ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                          ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1:1: 1:1 note: candidate #1: /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-e9599659.so
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                          ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1:1: 1:1 note: candidate #2: /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-e9599659.so
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                          ^
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1:1: 1:1 error: found possibly newer version of crate `core` which `std` depends on
| /home/buildbot_slave/buildbot/yocto-basic/obj/tmp/work/x86_64-poky-linux-gnueabi/rust-cross-arm/1.1.0-r0/rustc-1.1.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                                                          ^
| 

[codyps]

Unclear if this is solvable with current rustc behavior due to the need to link against our external llvm.

ie: we want dylibs, but we want to ignore the dylibs that aren't llvm. Rustc's command line doesn't let us do that.

Easy solution would be to ignore lib conflicts by selecting the first lib.

[codyps]

It's also possible that we might be able to adjust the hash rustc appends to libraries to include bitbake's PV + PR, which might aleviate our issues.

https://github.com/Heather/gentoo-rust/blob/master/dev-lang/rust/rust-1.2.0.ebuild#L50

[codyps]

Right now my workaround for this (error: multiple dylib candidates for std found) has been to cleansstate of the rust packages (native and cross) and retry.

[codyps]

rust-lang/rust#14650 might be adaptable to resolve this in rustc directly.

[codyps]

| CFG_LLVM_LINKAGE_FILE=/home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/rt/llvmdeps.rs LD_LIBRARY_PATH=/home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi:$LD_LIBRARY_PATH   x86_64-linux/stage0/bin/rustc --cfg stage0  -O --cfg rtopt -g -C rpath -C prefer-dynamic -Z no-landing-pads --target=x86_64-linux --sysroot "x86_64-linux/stage0" -L "x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib"  -W warnings -L "x86_64-linux/rt" -L "/home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib"    --out-dir x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib -C extra-filename=-d8ace771 /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/librustc_llvm/lib.rs
| info: now are following matches for libstd-*.so libraries:
| x86_64-linux/stage1/lib/arm-poky-linux-gnueabi/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 error: found possibly newer version of crate `core` which `std` depends on
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 note: perhaps this crate needs to be recompiled?
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 note: crate `core` path #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libcore-d8ace771.rlib
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libarena/lib.rs:1:1: 1:1 note: crate `std` path #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.rlib
| error: aborting due to 2 previous errors
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/mk/target.mk:171: recipe for target 'x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.arena' failed
| make: *** [x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.arena] Error 101
| make: *** Waiting for unfinished jobs....
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 error: found possibly newer version of crate `core` which `std` depends on
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 note: perhaps this crate needs to be recompiled?
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|                                                                                                  ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 note: crate `core` path #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libcore-d8ace771.rlib
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libflate/lib.rs:1:1: 1:1 note: crate `std` path #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.rlib
| error: aborting due to 2 previous errors
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                    ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                    ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgetopts/lib.rs:1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                    ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/mk/target.mk:171: recipe for target 'x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.flate' failed
| make: *** [x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.flate] Error 101
| error: aborting due to previous error
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/mk/target.mk:171: recipe for target 'x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.getopts' failed
| make: *** [x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.getopts] Error 101
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/liblog/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                ^
| error: aborting due to previous error
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                     ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                     ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libgraphviz/lib.rs:1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
|                                                                                                     ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1:1: 1:1 error: multiple dylib candidates for `std` found
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
|                                                                                                       ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1:1: 1:1 note: candidate #1: /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/build/x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
|                                                                                                       ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1:1: 1:1 note: candidate #2: /home/cody/obj/y/tmp/sysroots/x86_64-linux/usr/lib/rustlib/x86_64-linux/lib/libstd-d8ace771.so
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/src/libfmt_macros/lib.rs:1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
|                                                                                                       ^
| /home/cody/obj/y/tmp/work/x86_64-linux/rust-cross-arm/1.2.0-r0/rustc-1.2.0/mk/target.mk:171: recipe for target 'x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.log' failed
| make: *** [x86_64-linux/stage0/lib/arm-poky-linux-gnueabi/rustlib/x86_64-linux/lib/stamp.log] Error 101
| error: aborting due to previous error
| error: aborting due to previous error

[codyps]

It appears to reproduce easily by doing

# this one should complete, if not, clean both and retry
bitbake image-using-rust-native-and-rust-cross

# clean one out to force a rebuild
bitbake -c cleansstate rust-cross-arm

# this one fails with the error seen in this issue.
bitbake image-using-rust-native-and-rust-cross

A really bad work-around (that would only fix things for clean sysroots) might be to configure task dependencies to cause both rust variants to wait for the other before installing.

[codyps]

Alternately, a direct reproduction with bitbake:

mkdir src/llvm/b
cd src/llvm/b
../configure --prefix=$HOME/rust-prefix --enable-targets=x86,x86_64,arm,aarch64,mips,powerpc --enable-optimized --disable-assertions --disable-docs --enable-bindings=none --enable-keep-symbols
make -j10 && make install
cd ../../
mkdir b
../configure --llvm-root=$HOME/rust-prefix --prefix=$HOME/rust-prefix --disable-manage-submodules

# succeeds
make -j10 && make install

# force a rebuild
make clean

# fails due to  'error: multiple dylib candidates for `std` found'
make -j10 && make install

Because this error is being emitted by the rustc snapshot building stage0, we can't resolve this in meta-rust by patching the compiler itself, instead we need to look at adjusting the flags passed to the rustc snapshot to avoid it.