[clang] add llvm abi support

[RossComputerGuy]

This PR makes it possible to use the LLVM ABI which uses LLVM libc.

[llvmbot]

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-driver

Author: Tristan Ross (RossComputerGuy)

Changes

This PR makes it possible to use the LLVM ABI which uses LLVM libc.

---

Full diff: https://github.com/llvm/llvm-project/pull/121123.diff

2 Files Affected:

• (modified) clang/lib/Driver/Driver.cpp (+1-1)
• (modified) clang/lib/Driver/ToolChains/Gnu.cpp (+1-1)

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index dc84c1b9d1cc4e..98b8e6e97419c6 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1531,7 +1531,7 @@ Compilation *Driver::BuildCompilation(ArrayRef<const char *> ArgList) {
 
   // Check if the environment version is valid except wasm case.
   llvm::Triple Triple = TC.getTriple();
-  if (!Triple.isWasm()) {
+  if (!Triple.isWasm() && Triple.getEnvironment() != llvm::Triple::LLVM) {
     StringRef TripleVersionName = Triple.getEnvironmentVersionString();
     StringRef TripleObjectFormat =
         Triple.getObjectFormatTypeName(Triple.getObjectFormat());
diff --git a/clang/lib/Driver/ToolChains/Gnu.cpp b/clang/lib/Driver/ToolChains/Gnu.cpp
index 8397f1121ec2ce..2c9539ef56683c 100644
--- a/clang/lib/Driver/ToolChains/Gnu.cpp
+++ b/clang/lib/Driver/ToolChains/Gnu.cpp
@@ -464,7 +464,7 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
       if (!Args.hasArg(options::OPT_shared)) {
         if (Args.hasArg(options::OPT_pg))
           crt1 = "gcrt1.o";
-        else if (IsPIE)
+        else if (IsPIE && Triple.getEnvironment() != llvm::Triple::LLVM)
           crt1 = "Scrt1.o";
         else if (IsStaticPIE)
           crt1 = "rcrt1.o";

[carlocab]

Needs tests.

[llvm-beanz]

This seems wrong to me. Opting out of here makes me think there is something wrong with how the LLVM environment was implemented in the triple.

The Wasm case is special because (apparently) it is supported to pass arbitrary non-environment values in the triple (see discussion: #78655 (comment)).

[RossComputerGuy]

The problem I was running into was I'd get invalid version error. My assumption was that the LLVM ABI would not have a version because that would be the version of the entire LLVM stack. I didn't see any other ways when grepping the source that could disable the error.

[MaskRay]

NAK. While llvm libc can be used an overlay, it is not complete for standalone Linux server/desktop usage. Introducing a target triple has large ecosystem implication and should not be taken lightly.

[RossComputerGuy]

Why close? LLVM libc is maturing and one of the goals I had was to try using it in Nixpkgs to build whatever I can. LLVM libc doesn't work well in an overlay mode so we have to use full builds. It's true that a lot of functions are still missing or not implemented but by having the ability to properly specify it can make it easier to find what to do next. Also, from what I can tell Clang and LLVM itself have already gotten some support for the ABI. This PR simply unblocks 1 error which makes the ABI usable.

[jhuber6]

You can compile and run static C applications, I'm not sure what the threshold is before we can start adding support to make it usable in clang.

[carlocab]

Introducing a target triple has large ecosystem implication and should not be taken lightly.

To be fair this patch doesn't introduce a target triple, it only makes an existing one usable in Clang.

That said, I tend to agree with the review at #121123 (comment) that this doesn't seem like the right approach.

[RossComputerGuy]

That said, I tend to agree with the review at #121123 (comment) that this doesn't seem like the right approach.

Yeah I agree too, I'm not sure what the right approach is but that's one of the reasons why PR's get reviewed.