From 2fe70d89d91e0079764fe19b9c1d5cce01ac4711 Mon Sep 17 00:00:00 2001
From: tannevaled <tannevaled@users.noreply.github.com>
Date: Fri, 10 Jul 2026 19:03:46 +0200
Subject: [PATCH] fix(llvm.org): ship libc++/libc++abi/libunwind on linux
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The linux bottle built only compiler-rt as a runtime, so it shipped clang
with NO libc++ at all — no libc++.so, no headers (include/c++/v1). Anything
that requires `-stdlib=libc++` therefore fails with "'iostream'/'string'
file not found". Notably this blocks envoyproxy.io, which dropped
gcc/libstdc++ support in 1.21+ and must be built with libc++.

Add libcxx;libcxxabi;libunwind to LLVM_ENABLE_RUNTIMES on linux. This is
additive: CLANG_DEFAULT_CXX_STDLIB=libstdc++ keeps gcc's libstdc++ as the
default, and libc++ is now available on request (`-stdlib=libc++`). Darwin
keeps getting libc++ from the SDK, so the extra runtimes are linux-only.

Verified on x86-64 (Debian bullseye): the built bottle now ships
include/c++/v1 + libc++.so/libc++abi.so/libunwind.so, and the freshly
built clang++ -stdlib=libc++ compiles, links and runs a program using
<iostream>/<vector>.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 projects/llvm.org/package.yml | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/projects/llvm.org/package.yml b/projects/llvm.org/package.yml
index 1363f32974..8f3630f87e 100644
--- a/projects/llvm.org/package.yml
+++ b/projects/llvm.org/package.yml
@@ -40,9 +40,20 @@ build:
   script:
     # Building compiler-rt on darwin+aarch64 fails for versions less than
     # 14 with the below configuration. FIXME if possible, of course.
+    #
+    # On linux we ALSO build libc++/libc++abi/libunwind as runtimes so the
+    # bottle ships a usable libc++ (headers under include/c++/v1 + the
+    # shared libs). Without it, clang has no libc++ at all on linux — only
+    # gcc's libstdc++ (which stays the default via CLANG_DEFAULT_CXX_STDLIB
+    # below) — so anything requiring `-stdlib=libc++` (e.g. envoyproxy.io,
+    # which dropped gcc/libstdc++ support in 1.21+) fails with
+    # "'iostream'/'string' file not found". This is additive: libstdc++
+    # remains the default; libc++ is now available on request. Darwin gets
+    # libc++ from the SDK, so we only add these on linux.
     - run: |
         RUNTIMES="-DLLVM_ENABLE_RUNTIMES='compiler-rt'"
         if test "{{hw.platform}}" = "linux"; then
+          RUNTIMES="-DLLVM_ENABLE_RUNTIMES='compiler-rt;libcxx;libcxxabi;libunwind'"
           ARGS="$ARGS $RUNTIMES"
         elif semverator satisfies '>=14' {{version}}; then
           ARGS="$ARGS $RUNTIMES"