[libc-commits] [libc] [libc] major refactor of startup library (PR #76092)

[via libc-commits]

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@@ -0,0 +1,141 @@
+//===-- Implementation file of do_start -----------------------------------===//
+//
+// 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 "startup/linux/do_start.h"
+#include "src/__support/OSUtil/syscall.h"
+#include "src/__support/threads/thread.h"
+#include "src/stdlib/atexit.h"
+#include "src/stdlib/exit.h"
+#include "src/unistd/environ.h"
+
+#include <linux/auxvec.h>
+#include <linux/elf.h>
+#include <stdint.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+
+namespace LIBC_NAMESPACE {
+
+// TODO: this symbol will be moved to config.linux.app
+AppProperties app;
+
+using InitCallback = void(int, char **, char **);
+using FiniCallback = void(void);
+
+extern "C" int main(int argc, char **argv, char **envp);
+
+extern "C" {
+// These arrays are present in the .init_array and .fini_array sections.
+// The symbols are inserted by linker when it sees references to them.
+extern uintptr_t __preinit_array_start[];
+extern uintptr_t __preinit_array_end[];
+extern uintptr_t __init_array_start[];
+extern uintptr_t __init_array_end[];
+extern uintptr_t __fini_array_start[];
+extern uintptr_t __fini_array_end[];
+}
+
+static void call_init_array_callbacks(int argc, char **argv, char **env) {
+  size_t preinit_array_size = __preinit_array_end - __preinit_array_start;
+  for (size_t i = 0; i < preinit_array_size; ++i)
+    reinterpret_cast<InitCallback *>(__preinit_array_start[i])(argc, argv, env);
+  size_t init_array_size = __init_array_end - __init_array_start;
+  for (size_t i = 0; i < init_array_size; ++i)
+    reinterpret_cast<InitCallback *>(__init_array_start[i])(argc, argv, env);
+}
+
+static void call_fini_array_callbacks() {
+  size_t fini_array_size = __fini_array_end - __fini_array_start;
+  for (size_t i = fini_array_size; i > 0; --i)
+    reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
+}
+
+static ThreadAttributes main_thread_attrib;
+
+[[noreturn]] void do_start() {
+  auto tid = syscall_impl<long>(SYS_gettid);
+  if (tid <= 0)
+    syscall_impl<long>(SYS_exit, 1);
+  main_thread_attrib.tid = static_cast<int>(tid);
+
+  // After the argv array, is a 8-byte long NULL value before the array of env
+  // values. The end of the env values is marked by another 8-byte long NULL
+  // value. We step over it (the "+ 1" below) to get to the env values.
+  uint64_t *env_ptr = app.args->argv + app.args->argc + 1;
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michaelrj-google wrote:

this should probably still be `ArgVEntryType` (and same for end_marker)

https://github.com/llvm/llvm-project/pull/76092