add mips/mips64 compiler-rt fallbacks so that libgcc is not required

[vfreex]

This adds compiler-rt fallbacks for mips and mips64 arches.

Solves linking issues like rust-lang/rust#57820.

Signed-off-by: Yuxiang Zhu vfreex@gmail.com

[vfreex]

It looks like compiler-rt builds for mips targets were never run before. There are some build failures like this:

cargo:warning=mips64el-linux-gnuabi64-gcc: error: ./compiler-rt/lib/builtins/fp_mode.c: No such file or directory

That is because fp_mode.c was introduced in llvm 9 (https://github.com/llvm-mirror/compiler-rt/commits/master/lib/builtins/arm/fp_mode.c) however the CI system uses llvm 8 fork https://github.com/rust-lang/llvm-project.

Really like to have mips arches rolling without linking to libgcc. Not sure how to proceed now. But let me try fixing the CI error first.

[nivkner]

I see this includes fall-backs for __addtf3, __multf3 and __subtf3,
which are also missing from aarch64-unknown-linux-musl, as seen in #201 .
can this PR include those symbols for aarch64 so that issue can also be fixed?

[vfreex]

@nivkner I haven't checked aarch64 build. Would like to have them in another PR.
I think ideally we should have rust implementations for those missing functions eventually. Not sure what the rust developers' plan about that.

Getting rid of libgcc/libgcc_s will make cross compiling much easier (closer to golang's cross compiling experience)

[Amanieu]

This list should probably contain all the tf (long double) builtins from compiler-rt:

set(GENERIC_TF_SOURCES
  comparetf2.c
  extenddftf2.c
  extendsftf2.c
  fixtfdi.c
  fixtfsi.c
  fixtfti.c
  fixunstfdi.c
  fixunstfsi.c
  fixunstfti.c
  floatditf.c
  floatsitf.c
  floattitf.c
  floatunditf.c
  floatunsitf.c
  floatuntitf.c
  multc3.c
  trunctfdf2.c
  trunctfsf2.c
)

We can't implement these in Rust since Rust doesn't have a long double type.

[Amanieu]

Since the author is inactive, I'll make the requested changes in another PR.

[messense]

I'm getting the following error in https://github.com/messense/rust-musl-cross/runs/2181084617?check_suite_focus=true

  = note: /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /root/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/mips64-unknown-linux-muslabi64/lib/liblibc-66e0d59b0ec4686b.rlib(vfscanf.lo): in function `vfscanf':
          /build/musl-1.1.24/src/stdio/vfscanf.c:306: undefined reference to `__trunctfsf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /build/musl-1.1.24/src/stdio/vfscanf.c:306: undefined reference to `__trunctfsf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /build/musl-1.1.24/src/stdio/vfscanf.c:309: undefined reference to `__trunctfdf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /build/musl-1.1.24/src/stdio/vfscanf.c:309: undefined reference to `__trunctfdf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /root/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/mips64-unknown-linux-muslabi64/lib/liblibc-66e0d59b0ec4686b.rlib(floatscan.lo): in function `decfloat':
          /build/musl-1.1.24/src/internal/floatscan.c:304: undefined reference to `__trunctfdf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /build/musl-1.1.24/src/internal/floatscan.c:304: undefined reference to `__trunctfdf2'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /build/musl-1.1.24/src/internal/floatscan.c:172: undefined reference to `__divtf3'
          /usr/local/musl/bin/../lib/gcc/mips64-unknown-linux-muslabi64/9.2.0/../../../../mips64-unknown-linux-muslabi64/bin/ld: /root/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/mips64-unknown-linux-muslabi64/lib/liblibc-66e0d59b0ec4686b.rlib(fmodl.lo): in function `fmodl':
          /build/musl-1.1.24/src/math/fmodl.c:17: undefined reference to `__divtf3'

Is it resolvable by adding the missing sources like this PR does?

Edit: Opened #408