Provide a way of linking libgcc statically

[taralx]

gcc et al provide "-static-libgcc" for platforms where a link to libgcc_s.so is undesirable. I need similar functionality in rustc because the cloud I'm deploying to doesn't have that in its runtime.

See issue #29482 for some background.

/cc @alexcrichton

[alexcrichton]

I'd personally be interested in just doing this unconditionally, I don't recall if there's a technical reason to link to the dynamic version beyond "just because", but there may be a good reason to!

[taralx]

I seem to remember that libgcc keeps some singleton state around, so there's questions of how dynlibs avoid getting their own state. I could be wrong.

[ianlancetaylor]

Once upon a time, it was necessary to use libgcc_s in order to throw a C++ exception from one shared library to another. That is no longer true on systems that use the GNU linker or gold. See http://www.airs.com/blog/archives/166 for background.

[steveklabnik]

Triage: no changes i'm aware of

[sanmai-NL]

@alexcrichton: Could you please assess how hard it would be to implement this / provide instructions if you prefer for others to pick it up? Thanks.

[alexcrichton]

Sorry I don't think I understand enough about how this change would be done in Rust to write up such instructions or evaluate it.

[nehaljwani]

After inspecting the output from ...

$ diff <(echo 'int main() {}' | g++ -static-libgcc --verbose -xc++ - 2>&1 | tr ' ' '\n') \
       <(echo 'int main() {}' | g++ --verbose -xc++ - 2>&1 | tr ' ' '\n')
...
269a270
> -lgcc_s
271d271
< -lgcc_eh
272a273
> -lgcc_s
274d274
< -lgcc_eh
277,278c277,278
...

... a plausible workaround for this issue (tested on Linux only) could be:

$ cat linkerdriver.wrap 
#!/bin/bash

for arg do
  shift
  case $arg in
    (-lgcc_s) : ;;
       (*) set -- "$@" "$arg" ;;
  esac
done

# replace 'cc' with the linker driver you actually want to invoke (most likely $CC)
exec cc "$@" -lgcc_eh -lc

$ # Change linker env var according to your target
$ CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER=$PWD/linkerdriver.wrap cargo build --verbose --package <my-package>

$ ldd target/debug/my-binary
	linux-vdso.so.1 (0x00007ffcd291f000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f81c9656000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f81c9507000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f81c9501000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f81c930f000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f81ca741000)