.config

#
# Automatically generated file; DO NOT EDIT.
# Crosstool-NG Configuration
#
CT_CONFIGURE_has_make381=y
CT_MODULES=y

#
# Paths and misc options
#

#
# crosstool-NG behavior
#
# CT_OBSOLETE is not set
# CT_EXPERIMENTAL is not set
# CT_DEBUG_CT is not set

#
# Paths
#
CT_LOCAL_TARBALLS_DIR=""
CT_WORK_DIR="${CT_TOP_DIR}/.build"
CT_PREFIX_DIR="/x-tools/${CT_TARGET}"
CT_INSTALL_DIR="${CT_PREFIX_DIR}"
CT_RM_RF_PREFIX_DIR=y
CT_REMOVE_DOCS=y
CT_INSTALL_DIR_RO=y
CT_STRIP_HOST_TOOLCHAIN_EXECUTABLES=y
# CT_STRIP_TARGET_TOOLCHAIN_EXECUTABLES is not set

#
# Downloading
#
# CT_FORBID_DOWNLOAD is not set
# CT_FORCE_DOWNLOAD is not set
CT_CONNECT_TIMEOUT=10
# CT_ONLY_DOWNLOAD is not set
# CT_USE_MIRROR is not set

#
# Extracting
#
# CT_FORCE_EXTRACT is not set
CT_OVERIDE_CONFIG_GUESS_SUB=y
# CT_ONLY_EXTRACT is not set
CT_PATCH_BUNDLED=y
# CT_PATCH_LOCAL is not set
# CT_PATCH_BUNDLED_LOCAL is not set
# CT_PATCH_LOCAL_BUNDLED is not set
# CT_PATCH_BUNDLED_FALLBACK_LOCAL is not set
# CT_PATCH_LOCAL_FALLBACK_BUNDLED is not set
# CT_PATCH_NONE is not set
CT_PATCH_ORDER="bundled"

#
# Build behavior
#
CT_PARALLEL_JOBS=0
CT_LOAD=""
CT_USE_PIPES=y
CT_EXTRA_CFLAGS_FOR_BUILD=""
CT_EXTRA_LDFLAGS_FOR_BUILD=""
CT_EXTRA_CFLAGS_FOR_HOST=""
CT_EXTRA_LDFLAGS_FOR_HOST=""
# CT_CONFIG_SHELL_SH is not set
# CT_CONFIG_SHELL_ASH is not set
CT_CONFIG_SHELL_BASH=y
# CT_CONFIG_SHELL_CUSTOM is not set
CT_CONFIG_SHELL="${bash}"

#
# Logging
#
# CT_LOG_ERROR is not set
# CT_LOG_WARN is not set
CT_LOG_INFO=y
# CT_LOG_EXTRA is not set
# CT_LOG_ALL is not set
# CT_LOG_DEBUG is not set
CT_LOG_LEVEL_MAX="INFO"
# CT_LOG_SEE_TOOLS_WARN is not set
CT_LOG_PROGRESS_BAR=y
CT_LOG_TO_FILE=y
CT_LOG_FILE_COMPRESS=y

#
# Target options
#
CT_ARCH="x86"
CT_ARCH_SUPPORTS_32=y
CT_ARCH_SUPPORTS_64=y
CT_ARCH_SUPPORTS_WITH_ARCH=y
CT_ARCH_SUPPORTS_WITH_CPU=y
CT_ARCH_SUPPORTS_WITH_TUNE=y
CT_ARCH_DEFAULT_32=y
CT_ARCH_ARCH=""
CT_ARCH_CPU=""
CT_ARCH_TUNE=""
# CT_ARCH_32 is not set
CT_ARCH_64=y
CT_ARCH_BITNESS=64
CT_TARGET_CFLAGS=""
CT_TARGET_LDFLAGS=""
# CT_ARCH_alpha is not set
# CT_ARCH_arm is not set
# CT_ARCH_avr is not set
# CT_ARCH_m68k is not set
# CT_ARCH_mips is not set
# CT_ARCH_nios2 is not set
# CT_ARCH_powerpc is not set
# CT_ARCH_s390 is not set
# CT_ARCH_sh is not set
# CT_ARCH_sparc is not set
CT_ARCH_x86=y
# CT_ARCH_xtensa is not set
CT_ARCH_alpha_AVAILABLE=y
CT_ARCH_arm_AVAILABLE=y
CT_ARCH_avr_AVAILABLE=y
CT_ARCH_m68k_AVAILABLE=y
CT_ARCH_microblaze_AVAILABLE=y
CT_ARCH_mips_AVAILABLE=y
CT_ARCH_nios2_AVAILABLE=y
CT_ARCH_powerpc_AVAILABLE=y
CT_ARCH_s390_AVAILABLE=y
CT_ARCH_sh_AVAILABLE=y
CT_ARCH_sparc_AVAILABLE=y
CT_ARCH_x86_AVAILABLE=y
CT_ARCH_xtensa_AVAILABLE=y
CT_ARCH_SUFFIX=""

#
# Generic target options
#
# CT_MULTILIB is not set
CT_ARCH_USE_MMU=y

#
# Target optimisations
#
CT_ARCH_FLOAT=""
# CT_ARCH_ALPHA_EV4 is not set
# CT_ARCH_ALPHA_EV45 is not set
# CT_ARCH_ALPHA_EV5 is not set
# CT_ARCH_ALPHA_EV56 is not set
# CT_ARCH_ALPHA_EV6 is not set
# CT_ARCH_ALPHA_EV67 is not set

#
# Toolchain options
#

#
# General toolchain options
#
CT_FORCE_SYSROOT=y
CT_USE_SYSROOT=y
CT_SYSROOT_NAME="sysroot"
CT_SYSROOT_DIR_PREFIX=""
CT_WANTS_STATIC_LINK=y
# CT_STATIC_TOOLCHAIN is not set
CT_TOOLCHAIN_PKGVERSION=""
CT_TOOLCHAIN_BUGURL=""

#
# Tuple completion and aliasing
#
CT_TARGET_VENDOR="unknown"
CT_TARGET_ALIAS_SED_EXPR=""
CT_TARGET_ALIAS=""

#
# Toolchain type
#
CT_CROSS=y
# CT_CANADIAN is not set
CT_TOOLCHAIN_TYPE="cross"

#
# Build system
#
CT_BUILD=""
CT_BUILD_PREFIX=""
CT_BUILD_SUFFIX=""

#
# Misc options
#
# CT_TOOLCHAIN_ENABLE_NLS is not set

#
# Operating System
#
CT_KERNEL_SUPPORTS_SHARED_LIBS=y
CT_KERNEL="linux"
CT_KERNEL_VERSION="3.2.72"
# CT_KERNEL_bare_metal is not set
CT_KERNEL_linux=y
CT_KERNEL_bare_metal_AVAILABLE=y
CT_KERNEL_linux_AVAILABLE=y
# CT_KERNEL_V_4_3 is not set
# CT_KERNEL_V_4_2 is not set
# CT_KERNEL_V_4_1 is not set
# CT_KERNEL_V_3_18 is not set
# CT_KERNEL_V_3_14 is not set
# CT_KERNEL_V_3_12 is not set
# CT_KERNEL_V_3_10 is not set
# CT_KERNEL_V_3_4 is not set
CT_KERNEL_V_3_2=y
# CT_KERNEL_V_2_6_32 is not set
# CT_KERNEL_LINUX_CUSTOM is not set
CT_KERNEL_windows_AVAILABLE=y

#
# Common kernel options
#
CT_SHARED_LIBS=y

#
# linux other options
#
CT_KERNEL_LINUX_VERBOSITY_0=y
# CT_KERNEL_LINUX_VERBOSITY_1 is not set
# CT_KERNEL_LINUX_VERBOSITY_2 is not set
CT_KERNEL_LINUX_VERBOSE_LEVEL=0
CT_KERNEL_LINUX_INSTALL_CHECK=y

#
# Binary utilities
#
CT_ARCH_BINFMT_ELF=y
CT_BINUTILS="binutils"
CT_BINUTILS_binutils=y

#
# GNU binutils
#
# CT_CC_BINUTILS_SHOW_LINARO is not set
CT_BINUTILS_V_2_25_1=y
# CT_BINUTILS_V_2_25 is not set
# CT_BINUTILS_V_2_24 is not set
# CT_BINUTILS_V_2_23_2 is not set
# CT_BINUTILS_V_2_23_1 is not set
# CT_BINUTILS_V_2_22 is not set
# CT_BINUTILS_V_2_21_53 is not set
# CT_BINUTILS_V_2_21_1a is not set
# CT_BINUTILS_V_2_20_1a is not set
# CT_BINUTILS_V_2_19_1a is not set
# CT_BINUTILS_V_2_18a is not set
CT_BINUTILS_VERSION="2.25.1"
CT_BINUTILS_2_25_1_or_later=y
CT_BINUTILS_2_25_or_later=y
CT_BINUTILS_2_24_or_later=y
CT_BINUTILS_2_23_or_later=y
CT_BINUTILS_2_22_or_later=y
CT_BINUTILS_2_21_or_later=y
CT_BINUTILS_2_20_or_later=y
CT_BINUTILS_2_19_or_later=y
CT_BINUTILS_2_18_or_later=y
CT_BINUTILS_HAS_HASH_STYLE=y
CT_BINUTILS_HAS_GOLD=y
CT_BINUTILS_GOLD_SUPPORTS_ARCH=y
CT_BINUTILS_GOLD_SUPPORT=y
CT_BINUTILS_HAS_PLUGINS=y
CT_BINUTILS_HAS_PKGVERSION_BUGURL=y
CT_BINUTILS_LINKER_LD=y
# CT_BINUTILS_LINKER_GOLD is not set
# CT_BINUTILS_LINKER_LD_GOLD is not set
# CT_BINUTILS_LINKER_GOLD_LD is not set
CT_BINUTILS_LINKERS_LIST="ld"
CT_BINUTILS_LINKER_DEFAULT="bfd"
# CT_BINUTILS_PLUGINS is not set
CT_BINUTILS_EXTRA_CONFIG_ARRAY=""
# CT_BINUTILS_FOR_TARGET is not set

#
# binutils other options
#

#
# C-library
#
CT_LIBC="uClibc"
CT_LIBC_VERSION="1.0.9"
# CT_LIBC_glibc is not set
# CT_LIBC_musl is not set
# CT_LIBC_newlib is not set
# CT_LIBC_none is not set
CT_LIBC_uClibc=y
CT_LIBC_avr_libc_AVAILABLE=y
CT_LIBC_glibc_AVAILABLE=y
CT_THREADS="nptl"
# CT_LIBC_GLIBC_V_2_22 is not set
# CT_LIBC_GLIBC_V_2_21 is not set
# CT_LIBC_GLIBC_V_2_20 is not set
# CT_LIBC_GLIBC_V_2_19 is not set
# CT_LIBC_GLIBC_V_2_18 is not set
# CT_LIBC_GLIBC_V_2_17 is not set
# CT_LIBC_GLIBC_V_2_16_0 is not set
# CT_LIBC_GLIBC_V_2_15 is not set
# CT_LIBC_GLIBC_V_2_14_1 is not set
# CT_LIBC_GLIBC_V_2_14 is not set
# CT_LIBC_GLIBC_V_2_13 is not set
# CT_LIBC_GLIBC_V_2_12_2 is not set
# CT_LIBC_GLIBC_V_2_12_1 is not set
# CT_LIBC_GLIBC_V_2_11_1 is not set
# CT_LIBC_GLIBC_V_2_11 is not set
# CT_LIBC_GLIBC_V_2_10_1 is not set
# CT_LIBC_GLIBC_V_2_9 is not set
# CT_LIBC_GLIBC_V_2_8 is not set
CT_LIBC_mingw_AVAILABLE=y
CT_LIBC_musl_AVAILABLE=y
CT_LIBC_newlib_AVAILABLE=y
CT_LIBC_none_AVAILABLE=y
CT_LIBC_uClibc_AVAILABLE=y
CT_LIBC_UCLIBC_NG_V_1_0_9=y
# CT_LIBC_UCLIBC_V_0_9_33_2 is not set
CT_LIBC_UCLIBC_NG_1_0_9_or_later=y
CT_LIBC_UCLIBC_NG_1_0_0_or_later=y
CT_LIBC_UCLIBC_0_9_33_2_or_later=y
CT_LIBC_UCLIBC_PARALLEL=y
CT_LIBC_UCLIBC_NG=y
CT_LIBC_UCLIBC_VERBOSITY_0=y
# CT_LIBC_UCLIBC_VERBOSITY_1 is not set
# CT_LIBC_UCLIBC_VERBOSITY_2 is not set
CT_LIBC_UCLIBC_VERBOSITY=""
CT_LIBC_UCLIBC_DEBUG_LEVEL_0=y
# CT_LIBC_UCLIBC_DEBUG_LEVEL_1 is not set
# CT_LIBC_UCLIBC_DEBUG_LEVEL_2 is not set
# CT_LIBC_UCLIBC_DEBUG_LEVEL_3 is not set
CT_LIBC_UCLIBC_DEBUG_LEVEL=0
CT_LIBC_UCLIBC_CONFIG_FILE=""
CT_LIBC_SUPPORT_THREADS_ANY=y
CT_LIBC_SUPPORT_THREADS_NATIVE=y
CT_LIBC_SUPPORT_THREADS_LT=y
CT_LIBC_SUPPORT_THREADS_NONE=y

#
# Common C library options
#
CT_THREADS_NATIVE=y
# CT_THREADS_LT is not set
# CT_THREADS_NONE is not set
CT_LIBC_XLDD=y
# CT_LIBC_GLIBC_KERNEL_VERSION_NONE is not set
# CT_LIBC_GLIBC_KERNEL_VERSION_AS_HEADERS is not set
# CT_LIBC_GLIBC_KERNEL_VERSION_CHOSEN is not set

#
# uClibc other options
#
CT_LIBC_UCLIBC_LNXTHRD=""
# CT_LIBC_UCLIBC_LOCALES is not set
# CT_LIBC_UCLIBC_WCHAR is not set
CT_LIBC_UCLIBC_FENV=y

#
# C compiler
#
CT_CC="gcc"
CT_CC_CORE_PASSES_NEEDED=y
CT_CC_CORE_PASS_1_NEEDED=y
CT_CC_CORE_PASS_2_NEEDED=y
CT_CC_gcc=y
# CT_CC_GCC_SHOW_LINARO is not set
CT_CC_GCC_V_5_2_0=y
# CT_CC_GCC_V_4_9_3 is not set
# CT_CC_GCC_V_4_8_5 is not set
# CT_CC_GCC_V_4_7_4 is not set
# CT_CC_GCC_V_4_6_4 is not set
# CT_CC_GCC_V_4_5_4 is not set
# CT_CC_GCC_V_4_4_7 is not set
# CT_CC_GCC_V_4_3_6 is not set
# CT_CC_GCC_V_4_2_4 is not set
CT_CC_GCC_4_2_or_later=y
CT_CC_GCC_4_3_or_later=y
CT_CC_GCC_4_4_or_later=y
CT_CC_GCC_4_5_or_later=y
CT_CC_GCC_4_6_or_later=y
CT_CC_GCC_4_7_or_later=y
CT_CC_GCC_4_8_or_later=y
CT_CC_GCC_4_9_or_later=y
CT_CC_GCC_5=y
CT_CC_GCC_5_or_later=y
CT_CC_GCC_HAS_GRAPHITE=y
CT_CC_GCC_USE_GRAPHITE=y
CT_CC_GCC_HAS_LTO=y
CT_CC_GCC_USE_LTO=y
CT_CC_GCC_HAS_PKGVERSION_BUGURL=y
CT_CC_GCC_HAS_BUILD_ID=y
CT_CC_GCC_HAS_LNK_HASH_STYLE=y
CT_CC_GCC_USE_GMP_MPFR=y
CT_CC_GCC_USE_MPC=y
CT_CC_GCC_HAS_LIBQUADMATH=y
CT_CC_GCC_HAS_LIBSANITIZER=y
CT_CC_GCC_VERSION="5.2.0"
# CT_CC_LANG_FORTRAN is not set
CT_CC_GCC_ENABLE_CXX_FLAGS=""
CT_CC_GCC_CORE_EXTRA_CONFIG_ARRAY=""
CT_CC_GCC_EXTRA_CONFIG_ARRAY=""
CT_CC_GCC_EXTRA_ENV_ARRAY=""
CT_CC_GCC_STATIC_LIBSTDCXX=y
# CT_CC_GCC_SYSTEM_ZLIB is not set

#
# Optimisation features
#

#
# Settings for libraries running on target
#
CT_CC_GCC_ENABLE_TARGET_OPTSPACE=y
# CT_CC_GCC_LIBMUDFLAP is not set
# CT_CC_GCC_LIBGOMP is not set
# CT_CC_GCC_LIBSSP is not set
# CT_CC_GCC_LIBQUADMATH is not set

#
# Misc. obscure options.
#
CT_CC_CXA_ATEXIT=y
# CT_CC_GCC_DISABLE_PCH is not set
CT_CC_GCC_SJLJ_EXCEPTIONS=m
CT_CC_GCC_LDBL_128=m
# CT_CC_GCC_BUILD_ID is not set
CT_CC_GCC_LNK_HASH_STYLE_DEFAULT=y
# CT_CC_GCC_LNK_HASH_STYLE_SYSV is not set
# CT_CC_GCC_LNK_HASH_STYLE_GNU is not set
# CT_CC_GCC_LNK_HASH_STYLE_BOTH is not set
CT_CC_GCC_LNK_HASH_STYLE=""
CT_CC_GCC_DEC_FLOAT_AUTO=y
# CT_CC_GCC_DEC_FLOAT_BID is not set
# CT_CC_GCC_DEC_FLOAT_DPD is not set
# CT_CC_GCC_DEC_FLOATS_NO is not set
CT_CC_SUPPORT_CXX=y
CT_CC_SUPPORT_FORTRAN=y
CT_CC_SUPPORT_JAVA=y
CT_CC_SUPPORT_ADA=y
CT_CC_SUPPORT_OBJC=y
CT_CC_SUPPORT_OBJCXX=y
CT_CC_SUPPORT_GOLANG=y

#
# Additional supported languages:
#
CT_CC_LANG_CXX=y
# CT_CC_LANG_JAVA is not set

#
# Debug facilities
#
# CT_DEBUG_dmalloc is not set
# CT_DEBUG_duma is not set
# CT_DEBUG_gdb is not set
# CT_DEBUG_ltrace is not set
# CT_DEBUG_strace is not set

#
# Companion libraries
#
CT_COMPLIBS_NEEDED=y
CT_GMP_NEEDED=y
CT_MPFR_NEEDED=y
CT_ISL_NEEDED=y
CT_MPC_NEEDED=y
CT_COMPLIBS=y
CT_GMP=y
CT_MPFR=y
CT_ISL=y
CT_MPC=y
# CT_LIBICONV_V_1_14 is not set
CT_GMP_V_6_0_0=y
# CT_GMP_V_5_1_3 is not set
# CT_GMP_V_5_1_1 is not set
# CT_GMP_V_5_0_2 is not set
# CT_GMP_V_5_0_1 is not set
# CT_GMP_V_4_3_2 is not set
# CT_GMP_V_4_3_1 is not set
# CT_GMP_V_4_3_0 is not set
CT_GMP_5_0_2_or_later=y
CT_GMP_VERSION="6.0.0a"
CT_MPFR_V_3_1_3=y
# CT_MPFR_V_3_1_2 is not set
# CT_MPFR_V_3_1_0 is not set
# CT_MPFR_V_3_0_1 is not set
# CT_MPFR_V_3_0_0 is not set
# CT_MPFR_V_2_4_2 is not set
# CT_MPFR_V_2_4_1 is not set
# CT_MPFR_V_2_4_0 is not set
CT_MPFR_VERSION="3.1.3"
CT_ISL_V_0_14=y
# CT_ISL_V_0_12_2 is not set
CT_ISL_V_0_14_or_later=y
CT_ISL_V_0_12_or_later=y
CT_ISL_VERSION="0.14"
CT_MPC_V_1_0_3=y
# CT_MPC_V_1_0_2 is not set
# CT_MPC_V_1_0_1 is not set
# CT_MPC_V_1_0 is not set
# CT_MPC_V_0_9 is not set
# CT_MPC_V_0_8_2 is not set
# CT_MPC_V_0_8_1 is not set
# CT_MPC_V_0_7 is not set
CT_MPC_VERSION="1.0.3"

#
# Companion libraries common options
#
# CT_COMPLIBS_CHECK is not set

#
# Companion tools
#

#
# READ HELP before you say 'Y' below !!!
#
# CT_COMP_TOOLS is not set

rust-uclibc.md

Use a docker container to make this easy to replicate:

$ docker run -it ubuntu:16.04

Everything below this point must be executed inside the docker container

$ apt-get update

# stuff required to build Rust
$ apt-get install -y --no-install-recommends ca-certificates cmake curl file g++ gdb git libc6-dev make python

# build a uclibc cross toolchain from scratch using crosstool-ng
$ curl -sL https://raw.githubusercontent.com/rust-lang/rust-buildbot/a35c53e21a789cc782ec51f2fdefc1e3f8767c42/slaves/linux-cross/build_toolchain_root.sh | bash
# can't use crosstool-ng as root, so we create a new user
$ useradd -m rust
# and also create a folder for the toolchain
$ mkdir /x-tools
$ chown rust:rust /x-tools
$ su rust

# As `rust` user
$ mkdir ~/ct
$ cd ~/ct
# NOTE: Pick these options. Syntax: $MENU > $SUBMENU > $ITEM = $VALUE -- $COMMENT
# Path and misc options > Prefix directory = /x-tools/${CT_TARGET} 
# Target options > Target architecture = x86
# Target options > Bitness = 64
# Operating System > Linux kernel version = 3.2.72 -- Precise kernel
# Operating System > Target OS = linux
# C-library > C library = uClibc
# C compiler > C++ = ENABLE -- we'll need a C++ cross compiler for when cross compile rustc
$ ct-ng menuconfig
$ ct-ng build
$ exit

# Back as `root`
# Put some symlinks to the cross compiler in PATH
$ cd /usr/bin
$ ln -s /x-tools/x86_64-unknown-linux-uclibc/bin/x86_64-unknown-linux-uclibc-gcc x86_64-linux-uclibc-gcc
$ ln -s /x-tools/x86_64-unknown-linux-uclibc/bin/x86_64-unknown-linux-uclibc-g++ x86_64-linux-uclibc-g++
$ ln -s /x-tools/x86_64-unknown-linux-uclibc/bin/x86_64-unknown-linux-uclibc-ar x86_64-linux-uclibc-ar
# Test
$ x86_64-linux-uclibc-gcc -v
$ su rust

# Again as the `rust` user
# fetch the rust-lang/rust uclibc fork
# NOTE: I used the checkout of the commit "Resolve compile errors previously hidden under others"
$ git clone --depth 1 https://github.com/KennethAdamMiller/rust ~/rust

# tell gcc-rs which compiler to use
$ export CC_x86_64_unknown_linux_uclibc=x86_64-linux-uclibc-gcc
$ export CXX_x86_64_unknown_linux_uclibc=x86_64-linux-uclibc-g++
$ export AR_x86_64_unknown_linux_uclibc=x86_64-linux-uclibc-ar

# build it
$ mkdir ~/build
$ cd ~/build
$ ../rust/configure --enable-rustbuild --target=x86_64-unknown-linux-uclibc
# NOTE: fastest way to cross compile std -- this doesn't bootstrap (i.e. rebuild 3 times) the compiler
$ python ../rust/src/bootstrap/bootstrap.py --target x86_64-unknown-linux-uclibc --step libstd --stage 1

# test it
# use rustup to manage the new toolchain
$ curl https://sh.rustup.rs -sSf | sh -s -- -y
$ source ~/.cargo/env
$ rustup toolchain link stage1 build/x86_64-unknown-linux-gnu/stage1
$ rustup default stage1

# NOTE: output should say `-dev`
$ rustc -V
rustc 1.12.0-dev (5a8bb249f 2016-07-27)

$ echo 'fn main() { println!("Hello, world!") }' > hello.rs
$ rustc --target x86_64-unknown-linux-uclibc -C linker=x86_64-linux-uclibc-gcc hello.rs
$ file hello
hello: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib/ld64-uClibc.so.0, not stripped

Did yours complete successfully? Because I got an error that spat out:

unrecognized emulation mode: 64
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 i386linux elf_l1om elf_k1om

Also, I had to change the linker to be x86_64-linux-uclibc-ld, and add a new soft link, so I'll reply with an updated script when I'm done...

I think this may have been due tot the fact that in the source code, I added the line:
https://github.com/KennethAdamMiller/rust/blob/master/src/librustc_back/target/x86_64_unknown_linux_uclibc.rs#L7

So, I tried to manually enter in the command without the -m64 to see if that was the source of the error, but ultimately, I was subsequently was forced to remove every -Wl,XYZ option that the rust compiler emitted to the linker. It finally died with cannot find -lgcc_s, even when I added the location to the libgcc_s.so file within the built crosstool directory. So, I may have set something wrong in crosstool, but I have to investigate that further later on.

Did yours complete successfully?

I gotta admit I didn't test running all these commands again. Like I said before I wrote these down from what I remember (and my command line history), though I have done this procedure for other targets several times before.

Also, I had to change the linker to be x86_64-linux-uclibc-ld

Don't set ld as the linker, instead use x86_64-linux-uclibc-gcc as the linker. Rust only works correctly when gcc is the linker.

was forced to remove every -Wl,XYZ option

This is because you are using ld as the linker. If you use gcc as the linker, you won't see these errors.

It finally died with cannot find -lgcc_s

Same thing as above, use gcc instead of ld. ld doesn't know where the system libraries are installed; gcc does. gcc will call ld with the right arguments; it will tell ld where the system libraries are (via the -L flag iirc).

unrecognized emulation mode: 64

This sounds like the toolchain wasn't build with multillib enabled. crosstool-ng builds a toolchain with multilib disabled by default and iirc trying to build a toolchain with multilib enabled doesn't really/properly work. Also, you don't even need to pass -m64 in the first place; the toolchain is configured to generate 64-bit instructions by default and, in fact, it can't generate 32-bit instructions because multilib is disabled.

| I gotta admit I didn't test...

That's ok, I'm just really glad to have what I do, and I think I'm much further along that I otherwise would have been.

| Don't set ld...

Oh! ok, yeah the --linker= in the original part stopped without -gcc at the end, so I just thought that ld was of course the linker.

| You don't even need to pass -m64...

I removed it from the rust target and rebuilt it.

| sounds like the toolchain wasn't built with multilib enabled...

Ok, I'll build with that enabled and try again, although if multilib being enabled causes problems but is needed, I don't know what else I can do.

So far, just removing the -m64 part and changing the linker resulted in a different error, although I'm not sure how far along the compilation is to know which I was closer to being done with:

rust@aadce5e3f5cf:~/build$ rustc --target x86_64-unknown-linux-uclibc -C linker=x86_64-linux-uclibc-gcc hello.rs
error: linking with x86_64-linux-uclibc-gcc failed: exit code: 1
note: "x86_64-linux-uclibc-gcc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-L" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib" "hello.0.o" "-o" "hello" "-Wl,--gc-sections" "-pie" "-nodefaultlibs" "-L" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib" "-Wl,-Bstatic" "-Wl,-Bdynamic" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/libstd-ba34b5778cda2d40.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/libpanic_unwind-4468a2a640556f4f.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/libunwind-955053747c616610.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/librand-4a280e99d262760a.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/libcollections-8255c7ccacfdbe43.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/librustc_unicode-91a6a713af3719b4.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/liballoc-eeeed99c269728ee.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/liballoc_jemalloc-f2163600a65dc593.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/liblibc-f36fcda8a23729fd.rlib" "/home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/libcore-b0188cf7cfaaa310.rlib" "-l" "dl" "-l" "rt" "-l" "pthread" "-l" "gcc_s" "-l" "pthread" "-l" "c" "-l" "m" "-l" "rt" "-l" "util" "-l" "compiler-rt"
note: /home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/liballoc_jemalloc-f2163600a65dc593.rlib(jemalloc.pic.o): In function malloc_conf_init': /home/rust/rust/src/liballoc_jemalloc/../jemalloc/src/jemalloc.c:937: undefined reference tosecure_getenv'
/home/rust/x-tools/x86_64-unknown-linux-uclibc/lib/gcc/x86_64-unknown-linux-uclibc/5.2.0/../../../../x86_64-unknown-linux-uclibc/bin/ld: /home/rust/build/build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-uclibc/lib/liballoc_jemalloc-f2163600a65dc593.rlib(jemalloc.pic.o): unrecognized relocation (0x2a) in section `.text.malloc_conf_init'
/home/rust/x-tools/x86_64-unknown-linux-uclibc/lib/gcc/x86_64-unknown-linux-uclibc/5.2.0/../../../../x86_64-unknown-linux-uclibc/bin/ld: final link failed: Bad value

I think maybe the rust toolchain has it's own malloc implementation, and the ct-ng compiler toolchain has it's own malloc implementation, and they are fighting with one another.

So, searching around, I found this:

https://users.rust-lang.org/t/cross-compilation-not-working/4299/2

And so, after reading that just a little bit, I realize that that is probably right. I forked from the master branch of rust, and then in the script, we pulled from the rust buildbot. Do you think I should just rebase my commits onto the latest rust master, and re-perform the buildbot script step? I'm pretty sure, although I don't see the command myself, that at some point in the build process it pulled down a std version, and I was worrying to myself that the rust compiler version and the build std version were different.

Sorry about the delay. I don't get notified about these comments and I forget to check.

undefined reference tosecure_getenv
unrecognized relocation (0x2a) in section `.text.malloc_conf_init'

This sounds like you are using two different toolchains (which is bad): one to compile the C dependencies and one to link Rust crates. Did you export the CC_x86_64_unknown_linux_uclibc et al. variables before calling make? I think that you can confirm this if you look for the output files (these files contain the output of running e.g. alloc_jemalloc's build.rs) in the build directory ($ find -name output) and verify that x86_64-linux-uclibc-gcc appears in their contents. If instead you see cc being used to compile jemalloc, that means you didn't properly set the CC_* et al. variables.

Yeah, I did export that. I can ctrl+r for it and see that I have it set.

In any case, I will blow away my docker and start over.

Are you sure it's not that the particular rust standard library version was different from the rust I have forked? I'm seeing the downloads for rust beta from July 6th, and my fork occurred way after that... I may be over thinking it, my build is still running for the latest retry.

Are you sure it's not that the particular rust standard library version was different from the rust I have forked?

I don't think so, no. std is built from scratch; it doesn't depend on the snapshot's std.

I'm seeing the downloads for rust beta from July 6th

That's how the bootstrap process works; the initial compiler is the previous stable () release. () The bootstrap process just recently changed so we are not quite using stable releases yet; that's why a beta is used for now.

Ok, well I just reproduced my error with "undefined reference to secure_getenv", not sure what to do from here now.