Issue #16455 has been reported by luizluca (Luiz Angelo Daros de Luca).

----------------------------------------
Bug #16455: coroutine ucontext uses deprecated POSIX getcontext/swapcontext/makecontext, absent in musl
https://bugs.ruby-lang.org/issues/16455

* Author: luizluca (Luiz Angelo Daros de Luca)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.7.0p0 (2019-12-25 revision 647ee6f091)
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
Hello,

While building ruby 2.7.0 for mips with musl, it fails:


```
linking miniruby                                                                                   /home/luizluca/prog-local/openwrt/trunk/staging_dir/toolchain-mips_24kc_gcc-8.3.0_musl/lib/gcc/mips-openwrt-linux-musl/8.3.0/../../../../mips-openwrt-linux-musl/bin/ld: cont.o: in function `coroutine_initialize_main':                                                                                cont.c:(.text+0x36c): undefined reference to `getcontext'                                          /home/luizluca/prog-local/openwrt/trunk/staging_dir/toolchain-mips_24kc_gcc-8.3.0_musl/lib/gcc/mips-openwrt-linux-musl/8.3.0/../../../../mips-openwrt-linux-musl/bin/ld: cont.o: in function `fiber_setcontext':                                                                                         cont.c:(.text+0xde6): undefined reference to `swapcontext'                                         /home/luizluca/prog-local/openwrt/trunk/staging_dir/toolchain-mips_24kc_gcc-8.3.0_musl/lib/gcc/mips-openwrt
 -linux-musl/8.3.0/../../../../mips-openwrt-linux-musl/bin/ld: cont.o: in function `fiber_switch':                                                                                             cont.c:(.text+0x16b8): undefined reference to `makecontext'                                        collect2: error: ld returned 1 exit status                                                         make[3]: *** [Makefile:271: miniruby] Error 1
```

It seems that now ruby either uses native ASM code or ucontext for coroutine.
Both are unavailable in my crossbuild. It was building and running with 2.6.x:

```
configure:25935: checking native coroutine implementation for mips-linux-gnu                       configure:25976: result: no
```

With 2.7.0:

```
configure:26536: checking native coroutine implementation for mips-linux-gnu                       configure:26601: result: ucontext
```

I tried to disable it with --without-coroutine, --with-out-coroutine and --with-coroutine=no, but it is innocuous or try to use a "no" implementation.

It looks like this introduced the change https://github.com/ruby/ruby/commit/7291fef55c90b9ab6b3c22018b16972861b98c9d

And musl might never fix it:
https://wiki.musl-libc.org/open-issues.html





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