libc/startup/gpu/nvptx/start.cpp

   1 //===-- Implementation of crt for nvptx -----------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/__support/GPU/utils.h"
  10 #include "src/__support/RPC/rpc_client.h"
  11 #include "src/stdlib/atexit.h"
  12 #include "src/stdlib/exit.h"
  13
  14 extern "C" int main(int argc, char **argv, char **envp);
  15
  16 namespace LIBC_NAMESPACE {
  17
  18 extern "C" {
  19 // Nvidia's 'nvlink' linker does not provide these symbols. We instead need
  20 // to manually create them and update the globals in the loader implememtation.
  21 uintptr_t *__init_array_start [[gnu::visibility("protected")]];
  22 uintptr_t *__init_array_end [[gnu::visibility("protected")]];
  23 uintptr_t *__fini_array_start [[gnu::visibility("protected")]];
  24 uintptr_t *__fini_array_end [[gnu::visibility("protected")]];
  25 }
  26
  27 // Nvidia requires that the signature of the function pointers match. This means
  28 // we cannot support the extended constructor arguments.
  29 using InitCallback = void(void);
  30 using FiniCallback = void(void);
  31
  32 static void call_init_array_callbacks(int, char **, char **) {
  33   size_t init_array_size = __init_array_end - __init_array_start;
  34   for (size_t i = 0; i < init_array_size; ++i)
  35     reinterpret_cast<InitCallback *>(__init_array_start[i])();
  36 }
  37
  38 static void call_fini_array_callbacks() {
  39   size_t fini_array_size = __fini_array_end - __fini_array_start;
  40   for (size_t i = fini_array_size; i > 0; --i)
  41     reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
  42 }
  43
  44 } // namespace LIBC_NAMESPACE
  45
  46 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  47 _begin(int argc, char **argv, char **env) {
  48   // We want the fini array callbacks to be run after other atexit
  49   // callbacks are run. So, we register them before running the init
  50   // array callbacks as they can potentially register their own atexit
  51   // callbacks.
  52   LIBC_NAMESPACE::atexit(&LIBC_NAMESPACE::call_fini_array_callbacks);
  53   LIBC_NAMESPACE::call_init_array_callbacks(argc, argv, env);
  54 }
  55
  56 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  57 _start(int argc, char **argv, char **envp, int *ret) {
  58   // Invoke the 'main' function with every active thread that the user launched
  59   // the _start kernel with.
  60   __atomic_fetch_or(ret, main(argc, argv, envp), __ATOMIC_RELAXED);
  61 }
  62
  63 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  64 _end(int retval) {
  65   // To finis the execution we invoke all the callbacks registered via 'atexit'
  66   // and then exit with the appropriate return value.
  67   LIBC_NAMESPACE::exit(retval);
  68 }