[libc-commits] [libc] [libc] Generate a stub for libpthread.a (PR #200908)

[Alexey Samsonov via libc-commits]

https://github.com/vonosmas updated https://github.com/llvm/llvm-project/pull/200908

>From 07aa5cb5596ee485fbc245226bbb25b6c1ec15a2 Mon Sep 17 00:00:00 2001
From: Alexey Samsonov <vonosmas at gmail.com>
Date: Mon, 1 Jun 2026 19:07:59 +0000
Subject: [PATCH 1/2] [libc] Generate a stub for libpthread.a

---
 libc/lib/CMakeLists.txt | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/libc/lib/CMakeLists.txt b/libc/lib/CMakeLists.txt
index 08026e937be94..3414a5dd99161 100644
--- a/libc/lib/CMakeLists.txt
+++ b/libc/lib/CMakeLists.txt
@@ -56,6 +56,29 @@ foreach(archive IN ZIP_LISTS
   endif()
 endforeach()
 
+# Add empty archive libraries for compatibility with systems expecting certain
+# bits of libc to be located in separate files (e.g. libpthread).
+if(LLVM_LIBC_FULL_BUILD)
+  set(dummy_source "${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp")
+  if(NOT EXISTS "${dummy_source}")
+    file(WRITE "${dummy_source}" "/* empty static library stub */\n")
+  endif()
+
+  list(APPEND libc_empty_archive_names pthread)
+  list(APPEND libc_empty_archive_targets libpthread)
+  foreach(archive IN ZIP_LISTS
+          libc_empty_archive_names libc_empty_archive_targets)
+    add_library(${archive_1} STATIC "${dummy_source}")
+    set_target_properties(
+      ${archive_1}
+      PROPERTIES
+        ARCHIVE_OUTPUT_NAME ${archive_0}
+        ARCHIVE_OUTPUT_DIRECTORY ${LIBC_LIBRARY_DIR}
+    )
+    list(APPEND added_archive_targets ${archive_1})
+  endforeach()  
+endif()
+
 install(
   TARGETS ${added_archive_targets}
   ARCHIVE DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}

>From 53712a7a486097586398d77f865a9128a6220ced Mon Sep 17 00:00:00 2001
From: Alexey Samsonov <vonosmas at gmail.com>
Date: Tue, 16 Jun 2026 06:01:31 +0000
Subject: [PATCH 2/2] Alternative direct ar cqs invocation.

---
 libc/lib/CMakeLists.txt | 48 +++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/libc/lib/CMakeLists.txt b/libc/lib/CMakeLists.txt
index 3414a5dd99161..cdffa00284677 100644
--- a/libc/lib/CMakeLists.txt
+++ b/libc/lib/CMakeLists.txt
@@ -56,29 +56,6 @@ foreach(archive IN ZIP_LISTS
   endif()
 endforeach()
 
-# Add empty archive libraries for compatibility with systems expecting certain
-# bits of libc to be located in separate files (e.g. libpthread).
-if(LLVM_LIBC_FULL_BUILD)
-  set(dummy_source "${CMAKE_CURRENT_BINARY_DIR}/dummy.cpp")
-  if(NOT EXISTS "${dummy_source}")
-    file(WRITE "${dummy_source}" "/* empty static library stub */\n")
-  endif()
-
-  list(APPEND libc_empty_archive_names pthread)
-  list(APPEND libc_empty_archive_targets libpthread)
-  foreach(archive IN ZIP_LISTS
-          libc_empty_archive_names libc_empty_archive_targets)
-    add_library(${archive_1} STATIC "${dummy_source}")
-    set_target_properties(
-      ${archive_1}
-      PROPERTIES
-        ARCHIVE_OUTPUT_NAME ${archive_0}
-        ARCHIVE_OUTPUT_DIRECTORY ${LIBC_LIBRARY_DIR}
-    )
-    list(APPEND added_archive_targets ${archive_1})
-  endforeach()  
-endif()
-
 install(
   TARGETS ${added_archive_targets}
   ARCHIVE DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
@@ -93,6 +70,29 @@ foreach(file ${added_bitcode_targets})
   )
 endforeach()
 
+# Add empty archive libraries for compatibility with systems expecting certain
+# bits of libc to be located in separate files (e.g. libpthread).
+set(added_empty_archives "")
+if(LLVM_LIBC_FULL_BUILD AND ${LIBC_TARGET_OS} STREQUAL "linux")
+  list(APPEND libc_empty_archive_names pthread)
+  foreach(archive ${libc_empty_archive_names})
+    set(empty_archive_path ${LIBC_LIBRARY_DIR}/lib${archive}.a)
+    add_custom_command(
+      OUTPUT ${empty_archive_path}
+      COMMAND ${CMAKE_AR} cqs ${empty_archive_path}
+      COMMENT "Creating empty archive ${empty_archive_path}"
+      VERBATIM
+    )
+    list(APPEND added_empty_archives ${empty_archive_path})
+  endforeach()
+
+  install(
+    FILES ${added_empty_archives}
+    DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
+    COMPONENT libc
+  )
+endif()
+
 set(startup_target "")
 if(LLVM_LIBC_FULL_BUILD AND NOT LIBC_TARGET_OS_IS_BAREMETAL)
   # For now we will disable libc-startup installation for baremetal. The
@@ -109,6 +109,7 @@ endif()
 add_custom_target(install-libc
                   DEPENDS ${added_archive_targets}
                           ${added_bitcode_targets}
+                          ${added_empty_archives}
                           ${startup_target}
                           ${header_install_target}
                   COMMAND "${CMAKE_COMMAND}"
@@ -117,6 +118,7 @@ add_custom_target(install-libc
 add_custom_target(install-libc-stripped
                   DEPENDS ${added_archive_targets}
                           ${added_bitcode_targets}
+                          ${added_empty_archives}
                           ${startup_target}
                           ${header_install_target}
                   COMMAND "${CMAKE_COMMAND}"