[libcxx-commits] [libcxx] [libc++] Simplify the conditions for generating a linker script (PR #73151)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne created https://github.com/llvm/llvm-project/pull/73151

We really shouldn't be depending on far away configuration options like LLVM_HAVE_LINK_VERSION_SCRIPT here. This patch simplifies the enablement of the linker scripts and as a result gets rid of an undesirable dependency on HandleLLVMOptions.cmake.

As a drive-by, the patch also stops taking into account whether Python3 is available. This should have no bearing on whether we generate a linker script or not, which is required for correctness. If someone tries to build libc++ and generate a linker script but Python3 is not available, they should get an error instead of silently getting an incorrect installation of the library.

>From 8f6473e920026df0c9236979ecf7ad2629e92e14 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Wed, 22 Nov 2023 12:54:10 -0500
Subject: [PATCH] [libc++] Simplify the conditions for generating a linker
 script

We really shouldn't be depending on far away configuration options
like LLVM_HAVE_LINK_VERSION_SCRIPT here. This patch simplifies the
enablement of the linker scripts and as a result gets rid of an
undesirable dependency on HandleLLVMOptions.cmake.

As a drive-by, the patch also stops taking into account whether Python3
is available. This should have no bearing on whether we generate a linker
script or not, which is required for correctness. If someone tries to
build libc++ and generate a linker script but Python3 is not available,
they should get an error instead of silently getting an incorrect
installation of the library.
---
 libcxx/CMakeLists.txt | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
index cb708baacd91dec..843ccbd0ed92edb 100644
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -251,17 +251,18 @@ option(LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY
 
 # Generate and install a linker script inplace of libc++.so. The linker script
 # will link libc++ to the correct ABI library. This option is on by default
-# on UNIX platforms other than Apple unless
-# 'LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY' is on. This option is also
-# disabled when the ABI library is not specified or is specified to be "none".
-set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
-if (LLVM_HAVE_LINK_VERSION_SCRIPT AND NOT LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY
-      AND NOT LIBCXX_CXX_ABI STREQUAL "none"
-      AND Python3_EXECUTABLE
-      AND LIBCXX_ENABLE_SHARED)
-    set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE ON)
+# on UNIX platforms other than Apple unless we statically link libc++abi
+# inside libc++.so, we don't build libc++.so at all or we don't have any
+# ABI library.
+if (LIBCXX_STATICALLY_LINK_ABI_IN_SHARED_LIBRARY
+    OR NOT LIBCXX_ENABLE_SHARED
+    OR LIBCXX_CXX_ABI STREQUAL "none")
+  set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
+elseif(UNIX AND NOT APPLE)
+  set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE ON)
+else()
+  set(ENABLE_LINKER_SCRIPT_DEFAULT_VALUE OFF)
 endif()
-
 option(LIBCXX_ENABLE_ABI_LINKER_SCRIPT
       "Use and install a linker script for the given ABI library"
       ${ENABLE_LINKER_SCRIPT_DEFAULT_VALUE})