How to use `RUSTFLAGS` environment variable to link to library?

help
1

Hey,

I'm trying to build a static binary on an Alpine docker container. I use the environment variable RUSTFLAGS to set -C target-feature=+crt-static and build by cargo build --release --no-default-features --features with-dns-sd --target x86_64-unknown-linux-musl but my build failed with

...

-Wl,--gc-sections" "-static-pie" "-Wl,-z,relro,-z,now" "-Wl,-O1" "-nodefaultlibs" "/usr/local/rustup/toolchains/stable-x86_64-unknown-linux-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crtendS.o" "/usr/local/rustup/toolchains/stable-x86_64-unknown-linux-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/self-contained/crtn.o"
#9 1223.3   = note: /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: /usr/lib/libdns_sd.a(libdns_sd_la-compat.o): in function `query_resolver_callback':
#9 1223.3           compat.c:(.text+0x24c): undefined reference to `avahi_client_errno'
#9 1223.3           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: /usr/lib/libdns_sd.a(libdns_sd_la-compat.o): in function `reg_create_service':
#9 1223.3           compat.c:(.text+0x3f6): undefined reference to `avahi_entry_group_add_service_strlst'
#9 1223.3           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: compat.c:(.text+0x43e): undefined reference to `avahi_entry_group_add_service_subtype'
#9 1223.3           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: compat.c:(.text+0x450): undefined reference to `avahi_entry_group_commit'
#9 1223.3           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: /usr/lib/libdns_sd.a(libdns_sd_la-compat.o): in function `thread_func':
#9 1223.3           compat.c:(.text+0x575): undefined reference to `avahi_simple_poll_run'

...

#9 1223.3           collect2: error: ld returned 1 exit status
#9 1223.3           
#9 1223.3   = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
#9 1223.3   = note: use the `-l` flag to specify native libraries to link
#9 1223.3   = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib)

I understand that the linker failed to use/locate /usr/lib/libdns_sd.a. I tried various combinations of

"-C target-feature=+crt-static -C default-linker-libraries=yes"
"-C target-feature=+crt-static -l /usr/lib/libdns_sd.a"
"-C target-feature=+crt-static -L /usr/lib/"
"-C target-feature=+crt-static -C link-args=-Wl,-rpath,/usr/lib/

But none worked.

Within the source, an extern crate dns_sd is used which uses pkg_config::find_library("avahi-compat-libdns_sd").unwrap(); to locate the library.

Any ideas how to get the build working?
Thanks.

2

Alpine only ships libavahi as dynamic library, so there is nothing to statically link against.

3

Where did you get /usr/lib/libdns_sd.a from? The avahi-compat-libdns_sd package also only contains a dynamic library.

4

It's part of avahi-dev

https://pkgs.alpinelinux.org/contents?file=libdns_sd.a&path=&name=&branch=v3.19

5

I think libdns_sd.a depends on libavahi-common.a and libavahi-client.a: avahi/avahi-compat-libdns_sd/Makefile.am at 219a9c2459ac4e2aa29291ff6712248d48234b57 · avahi/avahi · GitHub Try linking against those too.

6

I tried to include it, but I think my syntax is wrong.

RUSTFLAGS="-C target-feature=+crt-static -l /usr/lib/libdns_sd.a -l /usr/lib/libavahi-client.a -l /usr/lib/libavahi-common.a"

produced

649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libdns_sd.a: No such file or directory
649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libavahi-client.a: No such file or directory
649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libavahi-common.a: No such file or directory
649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libdns_sd.a: No such file or directory
649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libavahi-client.a: No such file or directory
649.0           /usr/lib/gcc/x86_64-alpine-linux-musl/13.2.1/../../../../x86_64-alpine-linux-musl/bin/ld: cannot find -l/usr/lib/libavahi-common.a: No such file or directory
649.0           collect2: error: ld returned 1 exit status
649.0           
649.0 
649.1 error: could not compile `librespot` (bin "librespot") due to 1 previous error
------
7

I got it working with

RUSTFLAGS="-C target-feature=+crt-static -C link-arg=-L/usr/lib/ -C link-arg=-l:libdns_sd.a -C link-arg=-l:libavahi-client.a -C link-arg=-l:libavahi-common.a -C link-arg=-l:libdbus-1.a -C link-arg=-l:libintl.a"

It now compiles with out issue, but running the binary causes a segmentation fault....