[libc-commits] [libc] f88e9de - [libc] Generate a stub for libpthread.a (#200908)

[via libc-commits]

Author: Alexey Samsonov
Date: 2026-06-15T23:35:20-07:00
New Revision: f88e9de37a52abf9b269a7232bf4d4028bc4ace8

URL: https://github.com/llvm/llvm-project/commit/f88e9de37a52abf9b269a7232bf4d4028bc4ace8
DIFF: https://github.com/llvm/llvm-project/commit/f88e9de37a52abf9b269a7232bf4d4028bc4ace8.diff

LOG: [libc] Generate a stub for libpthread.a (#200908)

Several build systems / existing scripts assume that pthread functions
are exposed through separate library (`libpthread.so` / `libpthread.a`)
and thus use `-lpthread` flag explicitly. Since llvm-libc puts all the
pthread functions into the regular `libc`, teach the CMake build rules
to produce an empty static archive `libpthread.a` for compatibility
purposes.

Added: 
    

Modified: 
    libc/lib/CMakeLists.txt

Removed: 
    


################################################################################
diff  --git a/libc/lib/CMakeLists.txt b/libc/lib/CMakeLists.txt
index 08026e937be94..8ef0329471521 100644
--- a/libc/lib/CMakeLists.txt
+++ b/libc/lib/CMakeLists.txt
@@ -70,6 +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
+    )
+    install(
+      FILES ${empty_archive_path}
+      DESTINATION ${LIBC_INSTALL_LIBRARY_DIR}
+      COMPONENT libc
+    )
+    add_custom_target(empty-${archive} ALL DEPENDS ${empty_archive_path})
+    list(APPEND added_empty_archives empty-${archive})
+  endforeach()
+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
@@ -86,6 +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}"
@@ -94,6 +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}"