llvmPackages.compiler-rt: drop libc-free patch (#380213)

From 5eaae2daff7722ee01eee239e131ee1f62643abe Mon Sep 17 00:00:00 2001

From: Peter Waller <peter.waller@arm.com>

Date: Wed, 5 Feb 2025 19:46:15 +0000

Subject: [PATCH] [compiler-rt][AArch64] Enable libc-free builtins Linux build

Without this change, libc++abi.so.1.0 fails to link with:

```

error: undefined sybol: __aarch64_sme_accessible

```

This symbol is provided by baremetal libc's such as newlib.

In order to compile a libc with compiler-rt, it is necessary first to

build a compiler-rt with no dependency on libc to acquire the builtins.

The intended linux test requires getauxval which is provided by libc.

To that end, there are examples in the wild of building a compiler-rt

without libc by specifying -DCOMPILER_RT_BAREMETAL_BUILD=ON.

On Linux, this gives a builtins build with (almost) no libc dependencies.

See for example:

https://github.com/NixOS/nixpkgs/blob/d7fe3bcaca37e79d8b3cbde4dd69edeafbd35313/pkgs/development/compilers/llvm/common/compiler-rt/default.nix#L116-L118

```

  ] ++ lib.optionals (!haveLibc || bareMetal) [

    "-DCMAKE_C_COMPILER_WORKS=ON"

    "-DCOMPILER_RT_BAREMETAL_BUILD=ON"

```

The above specifies that a !haveLibc build sets

`-DCOMPILER_RT_BAREMETAL_BUILD`, which is done for example in a `pkgsLLVM` build.

AIUI, acquiring such a builtins build of compiler-rt is necessary to build a

pure LLVM toolchain, since builtins are required to build libc (and

libcxx is required to build a full compiler-rt).

The effect of falling back to unimplemented is that this early-stage

builtins build is incapable of doing function multiversioning tests and

falls back to behaving as-if the feature is unavailable.

This behaviour changed in

https://github.com/llvm/llvm-project/pull/119414, which introduced a

subtle change in semantics in the removal of

compiler-rt/lib/builtins/aarch64/sme-abi-init.c (definition of getauxval

macro, which was bracketed by `#if defined(__linux__)`) vs the new

definition which does not test for linux.

The proposed change is reinstating things as they were before #119414.

---

 compiler-rt/lib/builtins/cpu_model/aarch64.c | 2 +-

 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/builtins/cpu_model/aarch64.c b/lib/builtins/cpu_model/aarch64.c

index 4082fd62ea11a25..50438bcc7ddd885 100644

--- a/lib/builtins/cpu_model/aarch64.c

+++ b/lib/builtins/cpu_model/aarch64.c

@@ -80,7 +80,7 @@ struct {

 #include "aarch64/fmv/getauxval.inc"

 #elif defined(_WIN32)

 #include "aarch64/fmv/windows.inc"

-#elif defined(ENABLE_BAREMETAL_AARCH64_FMV)

+#elif defined(ENABLE_BAREMETAL_AARCH64_FMV) && !defined(__linux__)

 #include "aarch64/fmv/baremetal.inc"

 #else

 #include "aarch64/fmv/unimplemented.inc"

          url = "https://github.com/llvm/llvm-project/pull/99837/commits/14ae0a660a38e1feb151928a14f35ff0f4487351.patch";

          hash = "sha256-JykABCaNNhYhZQxCvKiBn54DZ5ZguksgCHnpdwWF2no=";

          relative = "compiler-rt";

        })

        # Fixes baremetal

        # PR: https://github.com/llvm/llvm-project/pull/125922

        ++ lib.optional (lib.versionAtLeast metadata.release_version "20") (

          metadata.getVersionFile "compiler-rt/libc-free.patch"

        );

        });

    in

    (

      {