[libunwind] [libc][libunwind] support build libunwind with libc (PR #84509)

[Schrodinger ZHU Yifan via cfe-commits]

https://github.com/SchrodingerZhu updated https://github.com/llvm/llvm-project/pull/84509

>From c7aa9678d9d9df752490c635810428ae37766fd3 Mon Sep 17 00:00:00 2001
From: Schrodinger ZHU Yifan <yifanzhu at rochester.edu>
Date: Fri, 8 Mar 2024 11:14:39 -0500
Subject: [PATCH] [libc][libunwind] support build libunwind with libc

---
 libunwind/CMakeLists.txt     | 13 ++++++++++++-
 libunwind/src/CMakeLists.txt |  3 +++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/libunwind/CMakeLists.txt b/libunwind/CMakeLists.txt
index b22ade0a7d71e..386c69e4728ee 100644
--- a/libunwind/CMakeLists.txt
+++ b/libunwind/CMakeLists.txt
@@ -47,6 +47,7 @@ option(LIBUNWIND_ENABLE_ARM_WMMX "Enable unwinding support for ARM WMMX register
 option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 option(LIBUNWIND_WEAK_PTHREAD_LIB "Use weak references to refer to pthread functions." OFF)
 option(LIBUNWIND_USE_COMPILER_RT "Use compiler-rt instead of libgcc" OFF)
+option(LIBUNWIND_USE_LLVM_LIBC "Build libunwind with LLVM's libc headers" OFF)
 option(LIBUNWIND_INCLUDE_DOCS "Build the libunwind documentation." ${LLVM_INCLUDE_DOCS})
 option(LIBUNWIND_INCLUDE_TESTS "Build the libunwind tests." ${LLVM_INCLUDE_TESTS})
 option(LIBUNWIND_IS_BAREMETAL "Build libunwind for baremetal targets." OFF)
@@ -65,6 +66,10 @@ cmake_dependent_option(LIBUNWIND_INSTALL_SHARED_LIBRARY
   "Install the shared libunwind library." ON
   "LIBUNWIND_ENABLE_SHARED;LIBUNWIND_INSTALL_LIBRARY" OFF)
 
+if (LIBUNWIND_USE_LLVM_LIBC AND LIBUNWIND_ENABLE_SHARED)
+  message(FATAL_ERROR "Cannot build libunwind as a shared library with LLVM's libc headers.")
+endif()
+
 if(MINGW)
   set(LIBUNWIND_DEFAULT_TEST_CONFIG "llvm-libunwind-mingw.cfg.in")
 elseif (LIBUNWIND_ENABLE_SHARED)
@@ -175,6 +180,11 @@ if (LIBUNWIND_USE_COMPILER_RT AND NOT LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   list(APPEND LIBUNWIND_LINK_FLAGS "-rtlib=compiler-rt")
 endif()
 
+if (LIBUNWIND_USE_LLVM_LIBC)
+  include_directories(SYSTEM ${LIBUNWIND_BINARY_DIR}/../libc/include/)
+  add_compile_flags_if_supported(-ffreestanding)
+endif()
+
 add_compile_flags_if_supported(-Werror=return-type)
 
 if (LIBUNWIND_ENABLE_CET)
@@ -286,7 +296,8 @@ if (LIBUNWIND_ENABLE_ARM_WMMX)
   add_compile_flags(-D__ARM_WMMX)
 endif()
 
-if(LIBUNWIND_IS_BAREMETAL)
+# for now, libc does not have dlsym; enable baremetal mode to avoid using dlsym
+if(LIBUNWIND_IS_BAREMETAL OR LIBUNWIND_USE_LLVM_LIBC)
   add_compile_definitions(_LIBUNWIND_IS_BAREMETAL)
 endif()
 
diff --git a/libunwind/src/CMakeLists.txt b/libunwind/src/CMakeLists.txt
index 780430ba70ba6..fbec7d4b5296b 100644
--- a/libunwind/src/CMakeLists.txt
+++ b/libunwind/src/CMakeLists.txt
@@ -182,6 +182,9 @@ endif()
 
 # Build the static library.
 add_library(unwind_static_objects OBJECT EXCLUDE_FROM_ALL ${LIBUNWIND_SOURCES} ${LIBUNWIND_HEADERS})
+if (LIBUNWIND_USE_LLVM_LIBC)
+  add_dependencies(unwind_static_objects libc-headers)
+endif()
 cxx_add_warning_flags(unwind_static_objects ${LIBUNWIND_ENABLE_WERROR} ${LIBUNWIND_ENABLE_PEDANTIC})
 if(CMAKE_C_COMPILER_ID STREQUAL MSVC)
   target_compile_options(unwind_static_objects PRIVATE /GR-)