Implement `sigsetjmp` and `siglongjmp` for darwin/aarch64 (#139555)

libc/config/darwin/aarch64/config.json

diff --git a/libc/config/darwin/aarch64/config.json b/libc/config/darwin/aarch64/config.json
new file mode 100644
index 0000000..c82f13e
--- /dev/null
+++ b/libc/config/darwin/aarch64/config.json
@@ -0,0 +1,8 @@
+{
+  "setjmp": {
+    "LIBC_CONF_SETJMP_AARCH64_RESTORE_PLATFORM_REGISTER": {
+      "value": false,
+      "doc": "Avoid setjmp saving the value of x18, and longjmp restoring it. The Apple AArch64 ABI specifies that this register is reserved and should not be used"
+    }
+  }
+}

libc/config/darwin/aarch64/entrypoints.txt

diff --git a/libc/config/darwin/aarch64/entrypoints.txt b/libc/config/darwin/aarch64/entrypoints.txt
index 308fc49..437eca7 100644
--- a/libc/config/darwin/aarch64/entrypoints.txt
+++ b/libc/config/darwin/aarch64/entrypoints.txt
@@ -101,6 +101,17 @@
     libc.src.stdlib.free
 )
 
+if(LLVM_LIBC_FULL_BUILD)
+  list(APPEND TARGET_LIBC_ENTRYPOINTS
+    # setjmp.h entrypoints
+    libc.src.setjmp.longjmp
+    libc.src.setjmp.setjmp
+    libc.src.setjmp.siglongjmp
+    libc.src.setjmp.sigsetjmp
+  )
+endif()
+
+
 set(TARGET_LIBM_ENTRYPOINTS
     # complex.h entrypoints
     libc.src.complex.creal

libc/config/darwin/aarch64/headers.txt

diff --git a/libc/config/darwin/aarch64/headers.txt b/libc/config/darwin/aarch64/headers.txt
index 86e7145..8f3d602 100644
--- a/libc/config/darwin/aarch64/headers.txt
+++ b/libc/config/darwin/aarch64/headers.txt
@@ -7,6 +7,7 @@
     libc.include.inttypes
     libc.include.limits
     libc.include.math
+    libc.include.setjmp
     libc.include.stdlib
     libc.include.string
     libc.include.strings

libc/src/setjmp/CMakeLists.txt

diff --git a/libc/src/setjmp/CMakeLists.txt b/libc/src/setjmp/CMakeLists.txt
index 239254f..50c8272 100644
--- a/libc/src/setjmp/CMakeLists.txt
+++ b/libc/src/setjmp/CMakeLists.txt
@@ -1,3 +1,9 @@
+# Process architecture-specific subdirectory FIRST to avoid missing targets.
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
+  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
+endif()
+
+# Then process OS-specific subdirectory
 if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
   add_object_library(
@@ -8,10 +14,6 @@
   )
 endif()
 
-if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
-  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
-endif()
-
 add_entrypoint_object(
   setjmp
   ALIAS

libc/src/setjmp/darwin/CMakeLists.txt

diff --git a/libc/src/setjmp/darwin/CMakeLists.txt b/libc/src/setjmp/darwin/CMakeLists.txt
new file mode 100644
index 0000000..b844c8c
--- /dev/null
+++ b/libc/src/setjmp/darwin/CMakeLists.txt
@@ -0,0 +1,12 @@
+add_object_library(
+  sigsetjmp_epilogue
+  HDRS
+    ../sigsetjmp_epilogue.h
+  SRCS
+    sigsetjmp_epilogue.cpp
+  DEPENDS
+    libc.src.__support.common
+    libc.src.__support.OSUtil.osutil
+    libc.hdr.types.jmp_buf
+    libc.hdr.types.sigset_t
+)

libc/src/setjmp/darwin/sigsetjmp_epilogue.cpp

diff --git a/libc/src/setjmp/darwin/sigsetjmp_epilogue.cpp b/libc/src/setjmp/darwin/sigsetjmp_epilogue.cpp
new file mode 100644
index 0000000..b2ca4d9
--- /dev/null
+++ b/libc/src/setjmp/darwin/sigsetjmp_epilogue.cpp
@@ -0,0 +1,21 @@
+//===-- Implementation of sigsetjmp_epilogue ------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/setjmp/sigsetjmp_epilogue.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/common.h"
+#include "src/signal/sigprocmask.h"
+
+namespace LIBC_NAMESPACE_DECL {
+[[gnu::returns_twice]] int sigsetjmp_epilogue(jmp_buf buffer, int retval) {
+  syscall_impl<long>(sigprocmask, SIG_SETMASK,
+                     /* set= */ retval ? &buffer->sigmask : nullptr,
+                     /* old_set= */ retval ? nullptr : &buffer->sigmask);
+  return retval;
+}
+} // namespace LIBC_NAMESPACE_DECL

libc/test/src/CMakeLists.txt

diff --git a/libc/test/src/CMakeLists.txt b/libc/test/src/CMakeLists.txt
index b7c1457..6dca47b 100644
--- a/libc/test/src/CMakeLists.txt
+++ b/libc/test/src/CMakeLists.txt
@@ -62,6 +62,7 @@
 add_subdirectory(fenv)
 add_subdirectory(math)
 add_subdirectory(search)
+add_subdirectory(setjmp)
 add_subdirectory(stdbit)
 add_subdirectory(stdfix)
 add_subdirectory(stdio)
@@ -92,7 +93,6 @@
 add_subdirectory(compiler)
 add_subdirectory(dirent)
 add_subdirectory(locale)
-add_subdirectory(setjmp)
 add_subdirectory(signal)
 add_subdirectory(spawn)