Building statically for x86_64-unknown-linux-musl

[anti-social]

I struggled building for x86_64-unknown-linux-musl. I used cross tool for this. What I found out is:

• there is a bug in librdkafka which leads to an errors when compiling without curl support: WITH_CURL off still tries to include curl.h confluentinc/librdkafka#5204 . So I had to fork librdkafka and apply a patch (there are PRs linked from the issue on the way, hope it will be fixed soon)
• then I tried to activate libz-static feature and got a lot of errors like:

 ...
 /usr/local/bin/../lib/gcc/x86_64-linux-musl/9.2.0/../../../../x86_64-linux-musl/bin/ld: /usr/include/x86_64-linux-gnu/bits/stdio2.h:67: undefined reference to `__snprintf_chk'
          collect2: error: ld returned 1 exit status

It turned out I should use cmake to cross-compile the library

• after that I got another error:

  CMake Error at /usr/local/share/cmake-3.23/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
    Could NOT find ZLIB (missing: ZLIB_LIBRARY ZLIB_INCLUDE_DIR)
  Call Stack (most recent call first):
    /usr/local/share/cmake-3.23/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
    /usr/local/share/cmake-3.23/Modules/FindZLIB.cmake:120 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
    src/CMakeLists.txt:221 (find_package)

I fixed it with a following change to build.rs:

@@ -238,7 +238,8 @@ fn build_librdkafka() {
         config.define("WITH_ZLIB", "1");
         config.register_dep("z");
         if let Ok(z_root) = env::var("DEP_Z_ROOT") {
-            cmake_library_paths.push(format!("{}/lib", z_root));
+            config.define("ZLIB_LIBRARY", format!("{}/include/lib/libz.a", z_root));
+            config.define("ZLIB_INCLUDE_DIR", format!("{}/include", z_root));
         }
     } else {
         config.define("WITH_ZLIB", "0");

• then I activated zstd, it failed with an error:

  CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
  Please set them or make sure they are set and tested correctly in the CMake files:
  /home/alexk/projects/rust-rdkafka/rdkafka-sys/librdkafka/src/ZSTD_INCLUDE_DIR
     used as include directory in directory /home/alexk/projects/rust-rdkafka/rdkafka-sys/librdkafka/src
  ZSTD_LIBRARY (ADVANCED)
      linked by target "rdkafka" in directory /home/alexk/projects/rust-rdkafka/rdkafka-sys/librdkafka/src

Finally after patching I managed to statically cross-compile my program for musl with all the features I needed:

@@ -302,6 +303,10 @@ fn build_librdkafka() {
     if env::var("CARGO_FEATURE_ZSTD").is_ok() {
         config.define("WITH_ZSTD", "1");
         config.register_dep("zstd");
+        if let Ok(zstd_root) = env::var("DEP_ZSTD_ROOT") {
+            config.define("ZSTD_LIBRARY_RELEASE", format!("{}/libzstd.a", zstd_root));
+            config.define("ZSTD_INCLUDE_DIR", format!("{}/include", zstd_root));
+        }
     } else {
         config.define("WITH_ZSTD", "0");
     }

I could try to make a PR with patches and readme section how to cross compile the library.