internal/rosa: llvm bootstrap artifacts

This bootstraps the LLVM toolchain across multiple artifacts.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/llvm.go

@@ -1,6 +1,7 @@
 package rosa
 
 import (
+	"runtime"
 	"slices"
 	"strconv"
 	"strings"
@@ -189,3 +190,115 @@ cp -r /system/include /usr/include && rm -rf /system/include
 		ScriptEarly: scriptEarly, Script: script + attr.script,
 	})
 }
+
+// NewLLVM returns LLVM toolchain across multiple [pkg.Artifact].
+func (t Toolchain) NewLLVM() (musl, compilerRT, runtimes, clang pkg.Artifact) {
+	var target string
+	switch runtime.GOARCH {
+	case "386", "amd64":
+		target = "X86"
+
+	default:
+		panic("unsupported target " + runtime.GOARCH)
+	}
+
+	minimalDeps := [][2]string{
+		{"LLVM_ENABLE_ZLIB", "OFF"},
+		{"LLVM_ENABLE_ZSTD", "OFF"},
+		{"LLVM_ENABLE_LIBXML2", "OFF"},
+	}
+
+	compilerRT = t.newLLVM("compiler-rt", &llvmAttr{
+		env: []string{
+			ldflags(false),
+		},
+		cmake: [][2]string{
+			// libc++ not yet available
+			{"CMAKE_CXX_COMPILER_TARGET", ""},
+
+			{"COMPILER_RT_BUILD_BUILTINS", "ON"},
+			{"COMPILER_RT_DEFAULT_TARGET_ONLY", "ON"},
+			{"LLVM_ENABLE_PER_TARGET_RUNTIME_DIR", "ON"},
+
+			// does not work without libunwind
+			{"COMPILER_RT_BUILD_CTX_PROFILE", "OFF"},
+			{"COMPILER_RT_BUILD_LIBFUZZER", "OFF"},
+			{"COMPILER_RT_BUILD_MEMPROF", "OFF"},
+			{"COMPILER_RT_BUILD_PROFILE", "OFF"},
+			{"COMPILER_RT_BUILD_SANITIZERS", "OFF"},
+			{"COMPILER_RT_BUILD_XRAY", "OFF"},
+		},
+		append: []string{"compiler-rt"},
+		extra: []pkg.Artifact{t.NewMusl(&MuslAttr{
+			Headers: true,
+			Env: []string{
+				"CC=clang",
+			},
+		})},
+		script: `
+mkdir -p "${ROSA_INSTALL_PREFIX}/lib/clang/21/lib/"
+ln -s \
+	"../../../${ROSA_TRIPLE}" \
+	"${ROSA_INSTALL_PREFIX}/lib/clang/21/lib/"
+
+ln -s \
+	"clang_rt.crtbegin-$(uname -m).o" \
+	"${ROSA_INSTALL_PREFIX}/lib/${ROSA_TRIPLE}/crtbeginS.o"
+ln -s \
+	"clang_rt.crtend-$(uname -m).o" \
+	"${ROSA_INSTALL_PREFIX}/lib/${ROSA_TRIPLE}/crtendS.o"
+`,
+	})
+
+	musl = t.NewMusl(&MuslAttr{
+		Extra: []pkg.Artifact{compilerRT},
+		Env: []string{
+			ldflags(false),
+			"CC=clang",
+			"LIBCC=/system/lib/clang/21/lib/" +
+				triplet() + "/libclang_rt.builtins.a",
+			"AR=ar",
+			"RANLIB=ranlib",
+		},
+	})
+
+	runtimes = t.newLLVM("runtimes", &llvmAttr{
+		env: []string{
+			ldflags(false),
+		},
+		flags: llvmRuntimeLibunwind | llvmRuntimeLibcxx | llvmRuntimeLibcxxABI,
+		cmake: slices.Concat([][2]string{
+			// libc++ not yet available
+			{"CMAKE_CXX_COMPILER_WORKS", "ON"},
+
+			{"LIBCXX_HAS_ATOMIC_LIB", "OFF"},
+			{"LIBCXXABI_HAS_CXA_THREAD_ATEXIT_IMPL", "OFF"},
+		}, minimalDeps),
+		append: []string{"runtimes"},
+		extra: []pkg.Artifact{
+			compilerRT,
+			musl,
+		},
+	})
+
+	clang = t.newLLVM("clang", &llvmAttr{
+		flags: llvmProjectClang | llvmProjectLld,
+		env: []string{
+			"CFLAGS=" + cflags,
+			"CXXFLAGS=" + cxxflags(),
+			ldflags(false),
+		},
+		cmake: slices.Concat([][2]string{
+			{"LLVM_TARGETS_TO_BUILD", target},
+			{"CMAKE_CROSSCOMPILING", "OFF"},
+			{"CXX_SUPPORTS_CUSTOM_LINKER", "ON"},
+		}, minimalDeps),
+		extra: []pkg.Artifact{
+			musl,
+			compilerRT,
+			runtimes,
+		},
+	})
+
+	return
+}