Cross compile from gnu to musl not working on Fedora 28

[dwaynebradley]

Here is what I'm seeing when trying to target x86_64-unknown-linux-musl on my Fedora 28 VM:

[dwayne@fedora-i3 openfmb-rust-sample-code]$ cargo build --target=x86_64-unknown-linux-musl
   Compiling openssl-sys v0.9.35
error: failed to run custom build command for `openssl-sys v0.9.35`
process didn't exit successfully: `/home/dwayne/git/openfmb-rust-sample-code/target/debug/build/openssl-sys-4d591416ba02a8e5/build-script-main` (exit code: 101)
--- stdout
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_LIB_DIR
cargo:rerun-if-env-changed=OPENSSL_LIB_DIR
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_INCLUDE_DIR
cargo:rerun-if-env-changed=OPENSSL_INCLUDE_DIR
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_DIR
cargo:rerun-if-env-changed=OPENSSL_DIR
run pkg_config fail: "Cross compilation detected. Use PKG_CONFIG_ALLOW_CROSS=1 to override"

--- stderr
thread 'main' panicked at '

Could not find directory of OpenSSL installation, and this `-sys` crate cannot
proceed without this knowledge. If OpenSSL is installed and this crate had
trouble finding it,  you can set the `OPENSSL_DIR` environment variable for the
compilation process.

Make sure you also have the development packages of openssl installed.
For example, `libssl-dev` on Ubuntu or `openssl-devel` on Fedora.

If you're in a situation where you think the directory *should* be found
automatically, please open a bug at https://github.com/sfackler/rust-openssl
and include information about your system as well as this message.

    $HOST = x86_64-unknown-linux-gnu
    $TARGET = x86_64-unknown-linux-musl
    openssl-sys = 0.9.35

', /home/dwayne/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/openssl-sys-0.9.35/build/main.rs:265:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.

I also tried to use the PKG_CONFIG_ALLOW_CROSS=1 option as well but then I get this:

[dwayne@fedora-i3 openfmb-rust-sample-code]$ PKG_CONFIG_ALLOW_CROSS=1 cargo build --target=x86_64-unknown-linux-musl
   Compiling openssl-sys v0.9.35
error: failed to run custom build command for `openssl-sys v0.9.35`
process didn't exit successfully: `/home/dwayne/git/openfmb-rust-sample-code/target/debug/build/openssl-sys-4d591416ba02a8e5/build-script-main` (exit code: 101)
--- stdout
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_LIB_DIR
cargo:rerun-if-env-changed=OPENSSL_LIB_DIR
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_INCLUDE_DIR
cargo:rerun-if-env-changed=OPENSSL_INCLUDE_DIR
cargo:rerun-if-env-changed=X86_64_UNKNOWN_LINUX_MUSL_OPENSSL_DIR
cargo:rerun-if-env-changed=OPENSSL_DIR
cargo:rustc-link-lib=ssl
cargo:rustc-link-lib=crypto
OPT_LEVEL = Some("0")
TARGET = Some("x86_64-unknown-linux-musl")
HOST = Some("x86_64-unknown-linux-gnu")
TARGET = Some("x86_64-unknown-linux-musl")
TARGET = Some("x86_64-unknown-linux-musl")
HOST = Some("x86_64-unknown-linux-gnu")
CC_x86_64-unknown-linux-musl = None
CC_x86_64_unknown_linux_musl = None
TARGET_CC = None
CC = None
HOST = Some("x86_64-unknown-linux-gnu")
CROSS_COMPILE = None
TARGET = Some("x86_64-unknown-linux-musl")
HOST = Some("x86_64-unknown-linux-gnu")
CFLAGS_x86_64-unknown-linux-musl = None
CFLAGS_x86_64_unknown_linux_musl = None
TARGET_CFLAGS = None
CFLAGS = None
DEBUG = Some("true")
running: "musl-gcc" "-O0" "-ffunction-sections" "-fdata-sections" "-fPIC" "-g" "-m64" "-static" "-Wall" "-Wextra" "-E" "/home/dwayne/git/openfmb-rust-sample-code/target/x86_64-unknown-linux-musl/debug/build/openssl-sys-8788530f8302f9f8/out/expando.c"
cargo:warning=/home/dwayne/git/openfmb-rust-sample-code/target/x86_64-unknown-linux-musl/debug/build/openssl-sys-8788530f8302f9f8/out/expando.c:1:10: fatal error: openssl/opensslv.h: No such file or directory
cargo:warning= #include <openssl/opensslv.h>
cargo:warning=          ^~~~~~~~~~~~~~~~~~~~
cargo:warning=compilation terminated.
exit code: 1

--- stderr
thread 'main' panicked at '
Header expansion error:
Error { kind: ToolExecError, message: "Command \"musl-gcc\" \"-O0\" \"-ffunction-sections\" \"-fdata-sections\" \"-fPIC\" \"-g\" \"-m64\" \"-static\" \"-Wall\" \"-Wextra\" \"-E\" \"/home/dwayne/git/openfmb-rust-sample-code/target/x86_64-unknown-linux-musl/debug/build/openssl-sys-8788530f8302f9f8/out/expando.c\" with args \"musl-gcc\" did not execute successfully (status code exit code: 1)." }

Failed to find OpenSSL development headers.

You can try fixing this setting the `OPENSSL_DIR` environment variable
pointing to your OpenSSL installation or installing OpenSSL headers package
specific to your distribution:

    # On Ubuntu
    sudo apt-get install libssl-dev
    # On Arch Linux
    sudo pacman -S openssl
    # On Fedora
    sudo dnf install openssl-devel

See rust-openssl README for more information:

    https://github.com/sfackler/rust-openssl#linux
', /home/dwayne/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/openssl-sys-0.9.35/build/main.rs:428:13
note: Run with `RUST_BACKTRACE=1` for a backtrace.

I have made sure that openssl-devel is installed:

[dwayne@fedora-i3 ~]$ sudo dnf install openssl-devel
Last metadata expiration check: 0:53:11 ago on Thu 23 Aug 2018 02:41:36 PM EDT.
Package openssl-devel-1:1.1.0h-3.fc28.x86_64 is already installed, skipping.
Dependencies resolved.
Nothing to do.
Complete!

pkg_config is installed as well:

[dwayne@fedora-i3 ~]$ pkg-config --list-package-names
mit-krb5-gssapi
mit-krb5
libxcrypt
jemalloc
krb5-gssapi
libpcre2-32
zlib
libselinux
openssl
kdb
libelf
fontutil
libpcre2-8
libsepol
libcrypt
kadm-server
libpcre2-16
kadm-client
libpcre2-posix
libpcap
com_err
libverto
krb5
libssl
libcrypto
gssrpc
shared-mime-info
gnome-keybindings
dracut
bash-completion
xbitmaps
libquvi-scripts-0.9
udev
systemd
[dwayne@fedora-i3 ~]$ pkg-config --list-all
mit-krb5-gssapi                mit-krb5-gssapi - Kerberos implementation of the GSSAPI
mit-krb5                       mit-krb5 - An implementation of Kerberos network authentication
libxcrypt                      libxcrypt - Extended crypt library for DES, MD5, Blowfish and others
jemalloc                       jemalloc - A general purpose malloc(3) implementation that emphasizes fragmentation avoidance and scalable concurrency support.
krb5-gssapi                    krb5-gssapi - Kerberos implementation of the GSSAPI
libpcre2-32                    libpcre2-32 - PCRE2 - Perl compatible regular expressions C library (2nd API) with 32 bit character support
zlib                           zlib - zlib compression library
libselinux                     libselinux - SELinux utility library
openssl                        OpenSSL - Secure Sockets Layer and cryptography libraries and tools
kdb                            kdb - Kerberos database access libraries
libelf                         libelf - elfutils libelf library to read and write ELF files
fontutil                       FontUtil - Font utilities dirs
libpcre2-8                     libpcre2-8 - PCRE2 - Perl compatible regular expressions C library (2nd API) with 8 bit character support
libsepol                       libsepol - SELinux policy library
libcrypt                       libxcrypt - Extended crypt library for DES, MD5, Blowfish and others
kadm-server                    kadm-server - Kerberos administration server library
libpcre2-16                    libpcre2-16 - PCRE2 - Perl compatible regular expressions C library (2nd API) with 16 bit character support
kadm-client                    kadm-client - Kerberos administration client library
libpcre2-posix                 libpcre2-posix - Posix compatible interface to libpcre2-8
libpcap                        libpcap - Platform-independent network traffic capture library
com_err                        com_err - Common error description library
libverto                       libverto - Event loop abstraction interface
krb5                           krb5 - An implementation of Kerberos network authentication
libssl                         OpenSSL-libssl - Secure Sockets Layer and cryptography libraries
libcrypto                      OpenSSL-libcrypto - OpenSSL cryptography library
gssrpc                         gssrpc - GSSAPI RPC implementation
shared-mime-info               shared-mime-info - Freedesktop common MIME database
gnome-keybindings              gnome-keybindings - Keybindings configuration for GNOME applications
dracut                         dracut - dracut
bash-completion                bash-completion - programmable completion for the bash shell
xbitmaps                       X bitmaps - Bitmaps that are shared between X applications
libquvi-scripts-0.9            libquvi-scripts - Scripts for libquvi
udev                           udev - udev
systemd                        systemd - systemd System and Service Manager

Anything else that I could try?

[sfackler]

You need to have a copy of OpenSSL that's cross compiled to MUSL as well, and point openssl-sys to it. Alternatively, you can use the vendored Cargo feature to have openssl-sys build a copy for you.

[dwaynebradley]

Thanks! That helped. I'm still learning my way around Rust. I had to add the following to my Cargo.toml file:

[dependencies]
nats = "*"
protobuf = { version = "~2.0" }
# Add openssl-sys as a direct dependency so it can be cross compiled to
# x86_64-unknown-linux-musl using the "vendored" feature below
openssl-sys = "*"

[features]
# Force openssl-sys to staticly link in the openssl library. Necessary when
# cross compiling to x86_64-unknown-linux-musl.
vendored = ["openssl-sys/vendored"]

This way I can compile to a single executable with no library dependencies using:

cargo build --target=x86_64-unknown-linux-musl --features vendored

[dwayne@fedora-i3 debug]$ ldd openfmb_rust_sample_code
	not a dynamic executable

If there is a better, more "rust" way, of doing this, I'm all ears!

[sfackler]

That's the way to do it!

[dwaynebradley]

Thanks!