[libcxx-commits] [libcxx] [libcxx] [docs] Update the MinGW build example (PR #68790)

[Martin Storsjö via libcxx-commits]

https://github.com/mstorsjo created https://github.com/llvm/llvm-project/pull/68790

The previous example wasn't a configuration that we actually test, but was a simplistic configuration with libstdc++ as ABI library.

The previous example configuration has bitrotted and broken in a couple different ways since it was added:

- In b0fd9497af6d2efd305e9eecfa0c1e265f1b2192, libcxx added uses of weak symbols that can be overridden by the user. GNU ld fails to export such weak symbols on MinGW, resulting in errors like: C:/msys64/mingw64/bin/ld: cannot export _ZNSt3__126__libcpp_assertion_handlerEPKciS1_S1_: symbol wrong type (2 vs 3) By switching to using LLD, -DLLVM_ENABLE_LLD=ON, alternatively -DCMAKE_SHARED_LINKER_FLAGS=-fuse-ld=lld, linking still succeeds.

- In a80e65e00ada7a9c16acf17a5fd40b4f12ced3a8, building with -DLIBCXX_CXX_ABI=libstdc++ in this configuration started failing. Switch to showing how to build with libcxxabi instead, which is the tested configuration and also is the typical configuration in how it most usually would be used on Windows.

These updates allow removing the mentions of the old caveats with the build configuration.

>From f0f791edf05189120c739fa810dc51f7e512f725 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Storsj=C3=B6?= <martin at martin.st>
Date: Wed, 11 Oct 2023 13:59:12 +0300
Subject: [PATCH] [libcxx] [docs] Update the MinGW build example

The previous example wasn't a configuration that we actually
test, but was a simplistic configuration with libstdc++ as ABI
library.

The previous example configuration has bitrotted and broken in
a couple different ways since it was added:

- In b0fd9497af6d2efd305e9eecfa0c1e265f1b2192, libcxx added uses
  of weak symbols that can be overridden by the user. GNU ld
  fails to export such weak symbols on MinGW, resulting in errors
  like:
    C:/msys64/mingw64/bin/ld: cannot export _ZNSt3__126__libcpp_assertion_handlerEPKciS1_S1_: symbol wrong type (2 vs 3)
  By switching to using LLD, -DLLVM_ENABLE_LLD=ON, alternatively
  -DCMAKE_SHARED_LINKER_FLAGS=-fuse-ld=lld, linking still succeeds.

- In a80e65e00ada7a9c16acf17a5fd40b4f12ced3a8, building with
  -DLIBCXX_CXX_ABI=libstdc++ in this configuration started failing.
  Switch to showing how to build with libcxxabi instead, which is
  the tested configuration and also is the typical configuration in
  how it most usually would be used on Windows.
---
 libcxx/docs/BuildingLibcxx.rst | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/libcxx/docs/BuildingLibcxx.rst b/libcxx/docs/BuildingLibcxx.rst
index e919e1e6f32bfc3..e33d2dce288d098 100644
--- a/libcxx/docs/BuildingLibcxx.rst
+++ b/libcxx/docs/BuildingLibcxx.rst
@@ -160,19 +160,13 @@ e.g. the ``mingw-w64-x86_64-clang`` package), together with CMake and ninja.
   > cmake -G Ninja -S runtimes -B build                                               \
           -DCMAKE_C_COMPILER=clang                                                    \
           -DCMAKE_CXX_COMPILER=clang++                                                \
-          -DLLVM_ENABLE_RUNTIMES=libcxx                                               \
-          -DLIBCXX_CXX_ABI=libstdc++
+          -DLLVM_ENABLE_LLD=ON                                                        \
+          -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi"                                   \
+          -DLIBCXXABI_ENABLE_SHARED=OFF                                               \
+          -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=ON
   > ninja -C build cxx
-  > cp /mingw64/bin/{libstdc++-6,libgcc_s_seh-1,libwinpthread-1}.dll lib
   > ninja -C build check-cxx
 
-As this build configuration ends up depending on a couple other DLLs that
-aren't available in path while running tests, copy them into the same
-directory as the tested libc++ DLL.
-
-(Building a libc++ that depends on libstdc++ isn't necessarily a config one
-would want to deploy, but it simplifies the config for testing purposes.)
-
 .. _`libc++abi`: http://libcxxabi.llvm.org/