[llvm] [CMake] Fix static Z3 linking order with pthread (PR #178393)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-support

Author: puneeth_aditya_5656 (mugiwaraluffy56)

<details>
<summary>Changes</summary>

## Summary
Fixes the link order when building LLVM with a static z3 library, which was causing "undefined reference to pthread_atfork" errors.

## Problem
When linking with static libz3.a, the linker fails because:
- pthread was being linked **before** z3
- Static linkers process left-to-right and discard unused symbols
- By the time z3 needed `pthread_atfork`, pthread symbols were already processed

## Solution
Move Z3 linking to occur **before** pthread is added to `system_libs`, ensuring correct order:


---
Full diff: https://github.com/llvm/llvm-project/pull/178393.diff


1 Files Affected:

- (modified) llvm/lib/Support/CMakeLists.txt (+8-5) 


``````````diff
diff --git a/llvm/lib/Support/CMakeLists.txt b/llvm/lib/Support/CMakeLists.txt
index 099b0e55579be..b13923f0ffb54 100644
--- a/llvm/lib/Support/CMakeLists.txt
+++ b/llvm/lib/Support/CMakeLists.txt
@@ -37,6 +37,14 @@ if(LLVM_ENABLE_ZSTD)
   list(APPEND imported_libs ${zstd_target})
 endif()
 
+# Link Z3 if the user wants to build it.
+# Note: Z3 must be linked before pthread because static libz3 depends on
+# pthread symbols (e.g., pthread_atfork). With static linking, library
+# order matters - dependent libraries must come before their dependencies.
+if(LLVM_WITH_Z3)
+  set(system_libs ${system_libs} ${Z3_LIBRARIES})
+endif()
+
 if( WIN32 )
   # libuuid required for FOLDERID_Profile usage in lib/Support/Windows/Path.inc.
   # advapi32 required for CryptAcquireContextW in lib/Support/Windows/Path.inc.
@@ -92,11 +100,6 @@ if (MSVC)
   set (delayload_flags $<$<NOT:$<LINK_LANGUAGE:Swift>>:delayimp ${WL}-delayload:shell32.dll ${WL}-delayload:ole32.dll>)
 endif()
 
-# Link Z3 if the user wants to build it.
-if(LLVM_WITH_Z3)
-  set(system_libs ${system_libs} ${Z3_LIBRARIES})
-endif()
-
 # Override the C runtime allocator on Windows and embed it into LLVM tools & libraries
 if(LLVM_INTEGRATED_CRT_ALLOC)
   if (NOT CMAKE_MSVC_RUNTIME_LIBRARY OR CMAKE_MSVC_RUNTIME_LIBRARY MATCHES "DLL$")

``````````

</details>


https://github.com/llvm/llvm-project/pull/178393