[Mips] use correct ld.so for musl soft float

[joewholden]

Summary

This patch attempts to fix the dynamic linker path for mips64-sf, I'm not entirely familiar with the llvm structure so I am unsure if this is the best way but I'd appreciate some feedback if not

[atanasyan]

1. Please include as much context as possible with your diff. This instruction helps to do that.
2. Such patch needs test case(s). Maybe it's enough to update the linux-ld.c test case which is failed now. Update failed cases and check both "soft" and "hard" float cases in this test.

[joewholden]

This is actually wrong anyway

[MaskRay]

In D80421#2081794, @joewholden wrote:

This is actually wrong anyway

If it is wrong, it should be abandoned. If it is correct, can you add some tests under clang/test/Driver and test with ninja check-clang-driver?

[joewholden]

I think this is better (we've been using it for a while successfully), I haven't had time to understand the tests enough to add some yet, but I'll take a look as soon as I can

[MaskRay]

Such driver tests are in clang/test/Driver/. You may want to read a few existing mips driver tests and musl tests to figure out whether reusing an existing file or creating a new file makes more sense.

You can run a test with $build/bin/llvm-lit -vv test.c. check-clang-driver runs all test/Driver tests. Before uploading a patch, check-clang-driver or check-clang (the latter if you suspect other components can be affected). For driver, check-clang-driver is usually sufficient.

clang/lib/Driver/ToolChains/Linux.cpp

   if (Triple.isMusl()) {
     std::string ArchName;
     bool IsArm = false;
+    bool IsMips = false;
 
     switch (Arch) {
     case llvm::Triple::arm:

       ArchName = "armeb";
       IsArm = true;
       break;
+    case llvm::Triple::mips:
+    case llvm::Triple::mipsel:
+      ArchName = "mips";
+      IsMips = true;
+      break;
+    case llvm::Triple::mips64:
+    case llvm::Triple::mips64el:
+      ArchName = "mips64";
+      IsMips = true;
+      break;
     default:
       ArchName = Triple.getArchName().str();
     }

         (Triple.getEnvironment() == llvm::Triple::MuslEABIHF ||
          tools::arm::getARMFloatABI(*this, Args) == tools::arm::FloatABI::Hard))
       ArchName += "hf";
+    if (IsMips && tools::mips::getMipsFloatABI(getDriver(), Args, getTriple()) == tools::mips::FloatABI::Soft)
+      ArchName += "-sf";
 
     return "/lib/ld-musl-" + ArchName + ".so.1";
   }