push sheeet

pkgs/development/compilers/llvm/common/compiler-rt/armv6-no-ldrexd-strexd.patch

@@ -0,0 +1,162 @@
+From 4fe3f21bf8b20c766877d2251d61118d0ff36688 Mon Sep 17 00:00:00 2001
+From: Ben Wolsieffer <benwolsieffer@gmail.com>
+Date: Wed, 7 Dec 2022 14:56:51 -0500
+Subject: [PATCH] [compiler-rt][builtins] Do not use ldrexd or strexd on ARMv6
+
+The ldrexd and strexd instructions are not available on base ARMv6, and were
+only added in ARMv6K (see [1]). This patch solves this problem once and for all
+using the __ARM_FEATURE_LDREX macro (see [2]) defined in the ARM C Language
+Extensions (ACLE). Although this macro is technically deprecated in the ACLE,
+it allows compiler-rt to reliably detect whether ldrexd and strexd are supported
+without complicated conditionals to detect different ARM architecture variants.
+
+[1] https://developer.arm.com/documentation/dht0008/a/ch01s02s01
+[2] https://arm-software.github.io/acle/main/acle.html#ldrexstrex
+
+Differential Revision: https://reviews.llvm.org/D139585
+---
+ compiler-rt/lib/builtins/arm/sync_fetch_and_add_8.S  | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_and_8.S  | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_max_8.S  | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_min_8.S  | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_nand_8.S | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_or_8.S   | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_sub_8.S  | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_umax_8.S | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_umin_8.S | 2 +-
+ compiler-rt/lib/builtins/arm/sync_fetch_and_xor_8.S  | 2 +-
+ 10 files changed, 10 insertions(+), 10 deletions(-)
+
+diff --git a/lib/builtins/arm/sync_fetch_and_add_8.S b/lib/builtins/arm/sync_fetch_and_add_8.S
+index 18bdd875b8b7..bee6f7ba0f34 100644
+--- a/lib/builtins/arm/sync_fetch_and_add_8.S
++++ b/lib/builtins/arm/sync_fetch_and_add_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define add_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     adds rD_LO, rN_LO, rM_LO ; \
+     adc rD_HI, rN_HI, rM_HI
+diff --git a/lib/builtins/arm/sync_fetch_and_and_8.S b/lib/builtins/arm/sync_fetch_and_and_8.S
+index 3716eff809d5..b4e77a54edf6 100644
+--- a/lib/builtins/arm/sync_fetch_and_and_8.S
++++ b/lib/builtins/arm/sync_fetch_and_and_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define and_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     and rD_LO, rN_LO, rM_LO ; \
+     and rD_HI, rN_HI, rM_HI
+diff --git a/lib/builtins/arm/sync_fetch_and_max_8.S b/lib/builtins/arm/sync_fetch_and_max_8.S
+index 06115ab55246..1813274cc649 100644
+--- a/lib/builtins/arm/sync_fetch_and_max_8.S
++++ b/lib/builtins/arm/sync_fetch_and_max_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define max_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI)         MINMAX_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI, gt)
+ 
+ SYNC_OP_8(max_8)
+diff --git a/lib/builtins/arm/sync_fetch_and_min_8.S b/lib/builtins/arm/sync_fetch_and_min_8.S
+index 4f3e299d95cc..fa8f3477757b 100644
+--- a/lib/builtins/arm/sync_fetch_and_min_8.S
++++ b/lib/builtins/arm/sync_fetch_and_min_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define min_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI)         MINMAX_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI, lt)
+ 
+ SYNC_OP_8(min_8)
+diff --git a/lib/builtins/arm/sync_fetch_and_nand_8.S b/lib/builtins/arm/sync_fetch_and_nand_8.S
+index 425c94474af7..fb27219ee200 100644
+--- a/lib/builtins/arm/sync_fetch_and_nand_8.S
++++ b/lib/builtins/arm/sync_fetch_and_nand_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define nand_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     bic rD_LO, rN_LO, rM_LO ; \
+     bic rD_HI, rN_HI, rM_HI
+diff --git a/lib/builtins/arm/sync_fetch_and_or_8.S b/lib/builtins/arm/sync_fetch_and_or_8.S
+index 4f18dcf84df9..3b077c8737b1 100644
+--- a/lib/builtins/arm/sync_fetch_and_or_8.S
++++ b/lib/builtins/arm/sync_fetch_and_or_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define or_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     orr rD_LO, rN_LO, rM_LO ; \
+     orr rD_HI, rN_HI, rM_HI
+diff --git a/lib/builtins/arm/sync_fetch_and_sub_8.S b/lib/builtins/arm/sync_fetch_and_sub_8.S
+index 25a4a1076555..c171607eabd8 100644
+--- a/lib/builtins/arm/sync_fetch_and_sub_8.S
++++ b/lib/builtins/arm/sync_fetch_and_sub_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define sub_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     subs rD_LO, rN_LO, rM_LO ; \
+     sbc rD_HI, rN_HI, rM_HI
+diff --git a/lib/builtins/arm/sync_fetch_and_umax_8.S b/lib/builtins/arm/sync_fetch_and_umax_8.S
+index aa5213ff1def..d1224f758049 100644
+--- a/lib/builtins/arm/sync_fetch_and_umax_8.S
++++ b/lib/builtins/arm/sync_fetch_and_umax_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define umax_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI)         MINMAX_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI, hi)
+ 
+ SYNC_OP_8(umax_8)
+diff --git a/lib/builtins/arm/sync_fetch_and_umin_8.S b/lib/builtins/arm/sync_fetch_and_umin_8.S
+index 8b40541ab47d..595444e6d053 100644
+--- a/lib/builtins/arm/sync_fetch_and_umin_8.S
++++ b/lib/builtins/arm/sync_fetch_and_umin_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define umin_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI)         MINMAX_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI, lo)
+ 
+ SYNC_OP_8(umin_8)
+diff --git a/lib/builtins/arm/sync_fetch_and_xor_8.S b/lib/builtins/arm/sync_fetch_and_xor_8.S
+index 7436eb1d4cae..9fc3d85cef75 100644
+--- a/lib/builtins/arm/sync_fetch_and_xor_8.S
++++ b/lib/builtins/arm/sync_fetch_and_xor_8.S
+@@ -13,7 +13,7 @@
+ 
+ #include "sync-ops.h"
+ 
+-#if __ARM_ARCH_PROFILE != 'M'
++#if __ARM_FEATURE_LDREX & 8
+ #define xor_8(rD_LO, rD_HI, rN_LO, rN_HI, rM_LO, rM_HI) \
+     eor rD_LO, rN_LO, rM_LO ; \
+     eor rD_HI, rN_HI, rM_HI
+-- 
+2.38.1
+

pkgs/development/compilers/llvm/common/compiler-rt/darwin-plistbuddy-workaround.patch

@@ -0,0 +1,25 @@
+CMake tries to read a list field from SDKSettings.plist, but the output of
+xcbuild PlistBuddy is incompatible with Apple's. (Plus we don't want it in our
+dependencies.)
+
+Simply assume ARM64 is supported by the SDK. We already limit the actual archs
+we build for by setting DARWIN_osx_BUILTIN_ARCHS explicitely.
+
+--- a/cmake/builtin-config-ix.cmake
++++ b/cmake/builtin-config-ix.cmake
+@@ -97,14 +97,7 @@ if(APPLE)
+   set(DARWIN_osx_BUILTIN_MIN_VER 10.5)
+   set(DARWIN_osx_BUILTIN_MIN_VER_FLAG
+       -mmacosx-version-min=${DARWIN_osx_BUILTIN_MIN_VER})
+-  set(DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
+-  # Add support for arm64 macOS if available in SDK.
+-  foreach(arch ${ARM64})
+-    sdk_has_arch_support(${DARWIN_osx_SYSROOT} macosx ${arch} MACOS_ARM_SUPPORT)
+-    if (MACOS_ARM_SUPPORT)
+-     list(APPEND DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${arch})
+-    endif()
+-  endforeach(arch)
++  set(DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64} ${ARM64})
+ 
+   if(COMPILER_RT_ENABLE_IOS)
+     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)

pkgs/development/compilers/llvm/common/compiler-rt/default.nix

@@ -0,0 +1,292 @@
+{
+  lib,
+  stdenv,
+  llvm_meta,
+  release_version,
+  version,
+  src ? null,
+  monorepoSrc ? null,
+  runCommand,
+  cmake,
+  ninja,
+  python3,
+  libllvm,
+  jq,
+  libcxx,
+  linuxHeaders,
+  freebsd,
+  libxcrypt,
+
+  # Some platforms have switched to using compiler-rt, but still want a
+  # libgcc.a for ABI compat purposes. The use case would be old code that
+  # expects to link `-lgcc` but doesn't care exactly what its contents
+  # are, so long as it provides some builtins.
+  doFakeLibgcc ? stdenv.hostPlatform.isFreeBSD,
+
+  # In recent releases, the compiler-rt build seems to produce
+  # many `libclang_rt*` libraries, but not a single unified
+  # `libcompiler_rt` library, at least under certain configurations. Some
+  # platforms still expect this, however, so we symlink one into place.
+  forceLinkCompilerRt ? stdenv.hostPlatform.isOpenBSD,
+  devExtraCmakeFlags ? [ ],
+  getVersionFile,
+  fetchpatch,
+}:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
+  # TODO: Make this account for GCC having libstdcxx, which will help
+  # use clean up the `cmakeFlags` rats nest below.
+  haveLibcxx = stdenv.cc.libcxx != null;
+  isDarwinStatic = stdenv.hostPlatform.isDarwin && stdenv.hostPlatform.isStatic;
+  inherit (stdenv.hostPlatform) isMusl isAarch64 isWindows;
+  noSanitizers = !haveLibc || bareMetal || isMusl || isDarwinStatic || isWindows;
+in
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "compiler-rt${lib.optionalString haveLibc "-libc"}";
+  inherit version;
+
+  src =
+    if monorepoSrc != null then
+      runCommand "compiler-rt-src-${version}" { inherit (monorepoSrc) passthru; } (
+        ''
+          mkdir -p "$out"
+          cp -r ${monorepoSrc}/cmake "$out"
+        ''
+        + lib.optionalString (lib.versionAtLeast release_version "21") ''
+          cp -r ${monorepoSrc}/third-party "$out"
+        ''
+        + ''
+          cp -r ${monorepoSrc}/compiler-rt "$out"
+        ''
+      )
+    else
+      src;
+
+  sourceRoot = "${finalAttrs.src.name}/compiler-rt";
+
+  patches = [
+    (getVersionFile "compiler-rt/X86-support-extension.patch") # Add support for i486 i586 i686 by reusing i386 config
+    # ld-wrapper dislikes `-rpath-link //nix/store`, so we normalize away the
+    # extra `/`.
+    (getVersionFile "compiler-rt/normalize-var.patch")
+    # Fix build on armv6l
+    ./armv6-no-ldrexd-strexd.patch
+    # See: https://github.com/NixOS/nixpkgs/pull/186575
+    ./darwin-plistbuddy-workaround.patch
+  ]
+  ++ [
+    (getVersionFile "compiler-rt/armv6-scudo-libatomic.patch")
+  ]
+  ++ lib.optional (lib.versions.major release_version == "19") (fetchpatch {
+    url = "https://github.com/llvm/llvm-project/pull/99837/commits/14ae0a660a38e1feb151928a14f35ff0f4487351.patch";
+    hash = "sha256-JykABCaNNhYhZQxCvKiBn54DZ5ZguksgCHnpdwWF2no=";
+    relative = "compiler-rt";
+  });
+
+  nativeBuildInputs = [
+    cmake
+    python3
+    libllvm.dev
+    ninja
+  ]
+  ++ lib.optionals stdenv.hostPlatform.isDarwin [ jq ];
+  buildInputs =
+    lib.optional (stdenv.hostPlatform.isLinux && stdenv.hostPlatform.isRiscV) linuxHeaders
+    ++ lib.optional (stdenv.hostPlatform.isFreeBSD) freebsd.include;
+
+  env = {
+    NIX_CFLAGS_COMPILE = toString (
+      [
+        "-DSCUDO_DEFAULT_OPTIONS=delete_size_mismatch=false:dealloc_type_mismatch=false"
+      ]
+      ++ lib.optionals (!haveLibc) [
+        # The compiler got stricter about this, and there is a usellvm patch below
+        # which patches out the assert include causing an implicit definition of
+        # assert. It would be nicer to understand why compiler-rt thinks it should
+        # be able to #include <assert.h> in the first place; perhaps it's in the
+        # wrong, or perhaps there is a way to provide an assert.h.
+        "-Wno-error=implicit-function-declaration"
+      ]
+    );
+
+    # Work around clang’s trying to invoke unprefixed-ld on Darwin when `-target` is passed.
+    NIX_CFLAGS_LINK = lib.optionalString (stdenv.hostPlatform.isDarwin) "--ld-path=${stdenv.cc.bintools}/bin/${stdenv.cc.targetPrefix}ld";
+  };
+
+  cmakeFlags = [
+    (lib.cmakeBool "COMPILER_RT_DEFAULT_TARGET_ONLY" true)
+    (lib.cmakeFeature "CMAKE_C_COMPILER_TARGET" stdenv.hostPlatform.config)
+    (lib.cmakeFeature "CMAKE_ASM_COMPILER_TARGET" stdenv.hostPlatform.config)
+  ]
+  ++ lib.optionals (haveLibc && stdenv.hostPlatform.libc == "glibc") [
+    (lib.cmakeFeature "SANITIZER_COMMON_CFLAGS" "-I${libxcrypt}/include")
+  ]
+  ++ lib.optionals (useLLVM && haveLibc && stdenv.cc.libcxx == libcxx) [
+    (lib.cmakeFeature "SANITIZER_CXX_ABI" "libcxxabi")
+    (lib.cmakeFeature "SANITIZER_CXX_ABI_LIBNAME" "libcxxabi")
+    (lib.cmakeBool "COMPILER_RT_USE_BUILTINS_LIBRARY" true)
+  ]
+  ++ lib.optionals (useLLVM && haveLibc) [
+    (lib.cmakeBool "COMPILER_RT_BUILD_SANITIZERS" true)
+    (lib.cmakeBool "COMPILER_RT_BUILD_PROFILE" true)
+  ]
+  ++ lib.optionals noSanitizers [
+    (lib.cmakeBool "COMPILER_RT_BUILD_SANITIZERS" false)
+  ]
+  ++ lib.optionals ((useLLVM && !haveLibcxx) || !haveLibc || bareMetal || isMusl || isDarwinStatic) [
+    (lib.cmakeBool "COMPILER_RT_BUILD_XRAY" false)
+    (lib.cmakeBool "COMPILER_RT_BUILD_LIBFUZZER" false)
+    (lib.cmakeBool "COMPILER_RT_BUILD_MEMPROF" false)
+    (lib.cmakeBool "COMPILER_RT_BUILD_ORC" false) # may be possible to build with musl if necessary
+  ]
+  ++ lib.optionals (!haveLibc || bareMetal) [
+    (lib.cmakeBool "COMPILER_RT_BUILD_PROFILE" false)
+    (lib.cmakeBool "CMAKE_C_COMPILER_WORKS" true)
+    (lib.cmakeBool "COMPILER_RT_BAREMETAL_BUILD" true)
+    (lib.cmakeFeature "CMAKE_SIZEOF_VOID_P" (toString (stdenv.hostPlatform.parsed.cpu.bits / 8)))
+  ]
+  ++ lib.optionals (!haveLibc || bareMetal || isDarwinStatic) [
+    (lib.cmakeBool "CMAKE_CXX_COMPILER_WORKS" true)
+  ]
+  ++ lib.optionals (!haveLibc) [
+    (lib.cmakeFeature "CMAKE_C_FLAGS" "-nodefaultlibs")
+  ]
+  ++ lib.optionals useLLVM [
+    (lib.cmakeBool "COMPILER_RT_BUILD_BUILTINS" true)
+    #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
+    (lib.cmakeFeature "CMAKE_TRY_COMPILE_TARGET_TYPE" "STATIC_LIBRARY")
+  ]
+  ++ lib.optionals bareMetal [
+    (lib.cmakeFeature "COMPILER_RT_OS_DIR" "baremetal")
+  ]
+  ++ lib.optionals (stdenv.hostPlatform.isDarwin) (
+    [
+      (lib.cmakeFeature "CMAKE_LIPO" "${lib.getBin stdenv.cc.bintools.bintools}/bin/${stdenv.cc.targetPrefix}lipo")
+    ]
+    ++ lib.optionals (!haveLibcxx) [
+      # Darwin fails to detect that the compiler supports the `-g` flag when there is no libc++ during the
+      # compiler-rt bootstrap, which prevents compiler-rt from building. The `-g` flag is required by the
+      # Darwin support, so force it to be enabled during the first stage of the compiler-rt bootstrap.
+      (lib.cmakeBool "COMPILER_RT_HAS_G_FLAG" true)
+    ]
+    ++ [
+      (lib.cmakeFeature "DARWIN_osx_ARCHS" stdenv.hostPlatform.darwinArch)
+      (lib.cmakeFeature "DARWIN_osx_BUILTIN_ARCHS" stdenv.hostPlatform.darwinArch)
+      (lib.cmakeFeature "SANITIZER_MIN_OSX_VERSION" stdenv.hostPlatform.darwinMinVersion)
+      # `COMPILER_RT_DEFAULT_TARGET_ONLY` does not apply to Darwin:
+      # https://github.com/llvm/llvm-project/blob/27ef42bec80b6c010b7b3729ed0528619521a690/compiler-rt/cmake/base-config-ix.cmake#L153
+      (lib.cmakeBool "COMPILER_RT_ENABLE_IOS" false)
+    ]
+  )
+  ++ lib.optionals (noSanitizers && lib.versionAtLeast release_version "19") [
+    (lib.cmakeBool "COMPILER_RT_BUILD_CTX_PROFILE" false)
+  ]
+  ++
+    lib.optional (stdenv.hostPlatform.isAarch64 && !haveLibc)
+      # Fixes https://github.com/NixOS/nixpkgs/issues/393603
+      (lib.cmakeBool "COMPILER_RT_DISABLE_AARCH64_FMV" true)
+  ++ devExtraCmakeFlags;
+
+  outputs = [
+    "out"
+    "dev"
+  ];
+
+  postPatch =
+    lib.optionalString (!stdenv.hostPlatform.isDarwin) ''
+      substituteInPlace cmake/builtin-config-ix.cmake \
+        --replace-fail 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+    ''
+    + lib.optionalString (!haveLibc) (
+      (lib.optionalString (lib.versions.major release_version == "18") ''
+        substituteInPlace lib/builtins/aarch64/sme-libc-routines.c \
+          --replace-fail "<stdlib.h>" "<stddef.h>"
+      '')
+      + ''
+        substituteInPlace lib/builtins/int_util.c \
+          --replace-fail "#include <stdlib.h>" ""
+      ''
+      + (lib.optionalString (!stdenv.hostPlatform.isFreeBSD)
+        # On FreeBSD, assert/static_assert are macros and allowing them to be implicitly declared causes link errors.
+        # see description above for why we're nuking assert.h normally but that doesn't work here.
+        # instead, we add the freebsd.include dependency explicitly
+        ''
+          substituteInPlace lib/builtins/clear_cache.c \
+            --replace-fail "#include <assert.h>" ""
+          substituteInPlace lib/builtins/cpu_model/x86.c \
+            --replace-fail "#include <assert.h>" ""
+        ''
+      )
+    )
+    +
+      lib.optionalString (lib.versionAtLeast release_version "19")
+        # codesign in sigtool doesn't support the various options used by the build
+        # and is present in the bootstrap-tools. Removing find_program prevents the
+        # build from trying to use it and failing.
+        ''
+          substituteInPlace cmake/Modules/AddCompilerRT.cmake \
+            --replace-fail 'find_program(CODESIGN codesign)' ""
+        '';
+
+  preConfigure = lib.optionalString stdenv.hostPlatform.isDarwin ''
+    cmakeFlagsArray+=(
+      "-DDARWIN_macosx_CACHED_SYSROOT=$SDKROOT"
+      "-DDARWIN_macosx_OVERRIDE_SDK_VERSION=$(jq -r .Version "$SDKROOT/SDKSettings.json")"
+    )
+  '';
+
+  # Hack around weird upstream RPATH bug
+  postInstall =
+    lib.optionalString (stdenv.hostPlatform.isDarwin) ''
+      ln -s "$out/lib"/*/* "$out/lib"
+    ''
+    + lib.optionalString (useLLVM && stdenv.hostPlatform.isLinux) ''
+      ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
+      ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
+      # Note the history of crt{begin,end}S in previous versions of llvm in nixpkg:
+      # The presence of crtbegin_shared has been added and removed; it's possible
+      # people have added/removed it to get it working on their platforms.
+      # Try each in turn for now.
+      ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbeginS.o
+      ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtendS.o
+      ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
+      ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
+    ''
+    + lib.optionalString doFakeLibgcc ''
+      ln -s $out/lib/*/libclang_rt.builtins-*.a $out/lib/libgcc.a
+    ''
+    + lib.optionalString forceLinkCompilerRt ''
+      ln -s $out/lib/*/libclang_rt.builtins-*.a $out/lib/libcompiler_rt.a
+    '';
+
+  meta = llvm_meta // {
+    homepage = "https://compiler-rt.llvm.org/";
+    description = "Compiler runtime libraries";
+    longDescription = ''
+      The compiler-rt project provides highly tuned implementations of the
+      low-level code generator support routines like "__fixunsdfdi" and other
+      calls generated when a target doesn't have a short sequence of native
+      instructions to implement a core IR operation. It also provides
+      implementations of run-time libraries for dynamic testing tools such as
+      AddressSanitizer, ThreadSanitizer, MemorySanitizer, and DataFlowSanitizer.
+    '';
+    # "All of the code in the compiler-rt project is dual licensed under the MIT
+    # license and the UIUC License (a BSD-like license)":
+    license = with lib.licenses; [
+      mit
+      ncsa
+    ];
+    broken =
+      # compiler-rt requires a Clang stdenv on 32-bit RISC-V:
+      # https://reviews.llvm.org/D43106#1019077
+      (stdenv.hostPlatform.isRiscV32 && !stdenv.cc.isClang)
+      # emutls wants `<pthread.h>` which isn't available (without experimental WASM threads proposal).
+      # `enable_execute_stack.c` Also doesn't sound like something WASM would support.
+      || (stdenv.hostPlatform.isWasm && haveLibc);
+  };
+})