Reland "[compiler-rt] Simple crtbegin.o and crtend.o implementation"

Clang relies on existence of certain symbols that are normally
provided by crtbegin.o/crtend.o. However, LLVM does not currently
provide implementation of these files, instead relying on either
libgcc or implementations provided as part of the system.

This change provides an initial implementation of crtbegin.o/crtend.o
that can be used on system that don't provide crtbegin.o/crtend.o as
part of their C library.

Differential Revision: https://reviews.llvm.org/D28791

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@359591 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 209 insertions, 0 deletions

diff --git a/lib/crt/CMakeLists.txt b/lib/crt/CMakeLists.txt
new file mode 100644
index 000000000..f0e8118e9
--- /dev/null
+++ b/lib/crt/CMakeLists.txt
@@ -0,0 +1,90 @@
+add_compiler_rt_component(crt)
+
+function(check_cxx_section_exists section output)
+  cmake_parse_arguments(ARG "" "" "SOURCE;FLAGS" ${ARGN})
+  if(NOT ARG_SOURCE)
+    set(ARG_SOURCE "int main() { return 0; }\n")
+  endif()
+
+  string(RANDOM TARGET_NAME)
+  set(TARGET_NAME "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/cmTC_${TARGET_NAME}.dir")
+  file(MAKE_DIRECTORY ${TARGET_NAME})
+
+  file(WRITE "${TARGET_NAME}/CheckSectionExists.c" "${ARG_SOURCE}\n")
+
+  string(REGEX MATCHALL "<[A-Za-z0-9_]*>" substitutions
+         ${CMAKE_C_COMPILE_OBJECT})
+
+  set(try_compile_flags "${ARG_FLAGS}")
+  if(CMAKE_C_COMPILER_ID MATCHES Clang AND CMAKE_C_COMPILER_TARGET)
+    list(APPEND try_compile_flags "-target ${CMAKE_C_COMPILER_TARGET}")
+  endif()
+
+  string(REPLACE ";" " " extra_flags "${try_compile_flags}")
+
+  set(test_compile_command "${CMAKE_C_COMPILE_OBJECT}")
+  foreach(substitution ${substitutions})
+    if(substitution STREQUAL "<CMAKE_C_COMPILER>")
+      string(REPLACE "<CMAKE_C_COMPILER>"
+             "${CMAKE_C_COMPILER}" test_compile_command ${test_compile_command})
+    elseif(substitution STREQUAL "<OBJECT>")
+      string(REPLACE "<OBJECT>" "${TARGET_NAME}/CheckSectionExists.o"
+             test_compile_command ${test_compile_command})
+    elseif(substitution STREQUAL "<SOURCE>")
+      string(REPLACE "<SOURCE>" "${TARGET_NAME}/CheckSectionExists.c"
+             test_compile_command ${test_compile_command})
+    elseif(substitution STREQUAL "<FLAGS>")
+      string(REPLACE "<FLAGS>" "${CMAKE_C_FLAGS} ${extra_flags}"
+             test_compile_command ${test_compile_command})
+    else()
+      string(REPLACE "${substitution}" "" test_compile_command
+             ${test_compile_command})
+    endif()
+  endforeach()
+
+  string(REPLACE " " ";" test_compile_command "${test_compile_command}")
+
+  execute_process(
+    COMMAND ${test_compile_command}
+    RESULT_VARIABLE TEST_RESULT
+    OUTPUT_VARIABLE TEST_OUTPUT
+    ERROR_VARIABLE TEST_ERROR
+  )
+
+  execute_process(
+    COMMAND ${CMAKE_OBJDUMP} -h "${TARGET_NAME}/CheckSectionExists.o"
+    RESULT_VARIABLE CHECK_RESULT
+    OUTPUT_VARIABLE CHECK_OUTPUT
+    ERROR_VARIABLE CHECK_ERROR
+  )
+  string(FIND "${CHECK_OUTPUT}" "${section}" SECTION_FOUND)
+
+  if(NOT SECTION_FOUND EQUAL -1)
+    set(${output} TRUE PARENT_SCOPE)
+  else()
+    set(${output} FALSE PARENT_SCOPE)
+  endif()
+
+  file(REMOVE_RECURSE ${TARGET_NAME})
+endfunction()
+
+check_cxx_section_exists(".init_array" COMPILER_RT_HAS_INITFINI_ARRAY
+  SOURCE "__attribute__((constructor)) void f() {}\nint main() { return 0; }\n")
+
+append_list_if(COMPILER_RT_HAS_INITFINI_ARRAY -DCRT_HAS_INITFINI_ARRAY CRT_CFLAGS)
+append_list_if(COMPILER_RT_HAS_FPIC_FLAG -fPIC CRT_CFLAGS)
+
+foreach(arch ${CRT_SUPPORTED_ARCH})
+  add_compiler_rt_runtime(clang_rt.crtbegin
+    OBJECT
+    ARCHS ${arch}
+    SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/crtbegin.c
+    CFLAGS ${CRT_CFLAGS}
+    PARENT_TARGET crt)
+  add_compiler_rt_runtime(clang_rt.crtend
+    OBJECT
+    ARCHS ${arch}
+    SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/crtend.c
+    CFLAGS ${CRT_CFLAGS}
+    PARENT_TARGET crt)
+endforeach()
diff --git a/lib/crt/crtbegin.c b/lib/crt/crtbegin.c
new file mode 100644
index 000000000..796094f65
--- /dev/null
+++ b/lib/crt/crtbegin.c
@@ -0,0 +1,97 @@
+//===-- crtbegin.c - Start of constructors and destructors ----------------===//
+//
+// 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 <stddef.h>
+
+__attribute__((visibility("hidden"))) void *__dso_handle = &__dso_handle;
+
+static void *__EH_FRAME_LIST__[]
+    __attribute__((section(".eh_frame"), aligned(sizeof(void *)))) = {};
+
+extern void __register_frame_info(const void *, void *) __attribute__((weak));
+extern void *__deregister_frame_info(const void *) __attribute__((weak));
+
+#ifndef CRT_HAS_INITFINI_ARRAY
+typedef void (*fp)(void);
+
+static fp __CTOR_LIST__[]
+    __attribute__((section(".ctors"), aligned(sizeof(fp)))) = {(fp)-1};
+extern fp __CTOR_LIST_END__[];
+#endif
+
+extern void __cxa_finalize(void *) __attribute__((weak));
+
+static void __attribute__((used)) __do_init() {
+  static _Bool __initialized;
+  if (__builtin_expect(__initialized, 0))
+    return;
+  __initialized = 1;
+
+  static struct { void *p[8]; } __object;
+  if (__register_frame_info)
+    __register_frame_info(__EH_FRAME_LIST__, &__object);
+
+#ifndef CRT_HAS_INITFINI_ARRAY
+  const size_t n = __CTOR_LIST_END__ - __CTOR_LIST__ - 1;
+  for (size_t i = n; i >= 1; i--) __CTOR_LIST__[i]();
+#endif
+}
+
+#ifdef CRT_HAS_INITFINI_ARRAY
+__attribute__((section(".init_array"),
+               used)) static void (*__init)(void) = __do_init;
+#else  // CRT_HAS_INITFINI_ARRAY
+#if defined(__i386__) || defined(__x86_64__)
+asm(".pushsection .init,\"ax\",@progbits\n\t"
+    "call " __USER_LABEL_PREFIX__ "__do_init\n\t"
+    ".popsection");
+#elif defined(__arm__)
+asm(".pushsection .init,\"ax\",%progbits\n\t"
+    "bl " __USER_LABEL_PREFIX__ "__do_init\n\t"
+    ".popsection");
+#endif  // CRT_HAS_INITFINI_ARRAY
+#endif
+
+#ifndef CRT_HAS_INITFINI_ARRAY
+static fp __DTOR_LIST__[]
+    __attribute__((section(".dtors"), aligned(sizeof(fp)))) = {(fp)-1};
+extern fp __DTOR_LIST_END__[];
+#endif
+
+static void __attribute__((used)) __do_fini() {
+  static _Bool __finalized;
+  if (__builtin_expect(__finalized, 0))
+    return;
+  __finalized = 1;
+
+  if (__cxa_finalize)
+    __cxa_finalize(__dso_handle);
+
+#ifndef CRT_HAS_INITFINI_ARRAY
+  if (__deregister_frame_info)
+    __deregister_frame_info(__EH_FRAME_LIST__);
+
+  const size_t n = __DTOR_LIST_END__ - __DTOR_LIST__ - 1;
+  for (size_t i = 1; i < n; i++) __DTOR_LIST__[i]();
+#endif
+}
+
+#ifdef CRT_HAS_INITFINI_ARRAY
+__attribute__((section(".fini_array"),
+               used)) static void (*__fini)(void) = __do_fini;
+#else  // CRT_HAS_INITFINI_ARRAY
+#if defined(__i386__) || defined(__x86_64__)
+asm(".pushsection .fini,\"ax\",@progbits\n\t"
+    "call " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+    ".popsection");
+#elif defined(__arm__)
+asm(".pushsection .fini,\"ax\",%progbits\n\t"
+    "bl " __USER_LABEL_PREFIX__ "__do_fini\n\t"
+    ".popsection");
+#endif
+#endif  // CRT_HAS_INIT_FINI_ARRAY
diff --git a/lib/crt/crtend.c b/lib/crt/crtend.c
new file mode 100644
index 000000000..ebcc60b89
--- /dev/null
+++ b/lib/crt/crtend.c
@@ -0,0 +1,22 @@
+//===-- crtend.c - End of constructors and destructors --------------------===//
+//
+// 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 <stdint.h>
+
+// Put 4-byte zero which is the length field in FDE at the end as a terminator.
+const int32_t __EH_FRAME_LIST_END__[]
+    __attribute__((section(".eh_frame"), aligned(sizeof(int32_t)),
+                   visibility("hidden"), used)) = {0};
+
+#ifndef CRT_HAS_INITFINI_ARRAY
+typedef void (*fp)(void);
+fp __CTOR_LIST_END__[]
+    __attribute__((section(".ctors"), visibility("hidden"), used)) = {0};
+fp __DTOR_LIST_END__[]
+    __attribute__((section(".dtors"), visibility("hidden"), used)) = {0};
+#endif