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 "config/gpu/app.h"
  10 #include "src/__support/GPU/utils.h"
  11 #include "src/__support/RPC/rpc_client.h"
  12 #include "src/__support/macros/config.h"
  13 #include "src/stdlib/atexit.h"
  14 #include "src/stdlib/exit.h"
  15
  16 extern "C" int main(int argc, char **argv, char **envp);
  17
  18 namespace LIBC_NAMESPACE_DECL {
  19
  20 DataEnvironment app;
  21
  22 // FIXME: Factor this out into common logic so we don't need to stub it here.
  23 void teardown_main_tls() {}
  24
  25 extern "C" {
  26 // Nvidia's 'nvlink' linker does not provide these symbols. We instead need
  27 // to manually create them and update the globals in the loader implememtation.
  28 uintptr_t *__init_array_start [[gnu::visibility("protected")]];
  29 uintptr_t *__init_array_end [[gnu::visibility("protected")]];
  30 uintptr_t *__fini_array_start [[gnu::visibility("protected")]];
  31 uintptr_t *__fini_array_end [[gnu::visibility("protected")]];
  32 }
  33
  34 // Nvidia requires that the signature of the function pointers match. This means
  35 // we cannot support the extended constructor arguments.
  36 using InitCallback = void(void);
  37 using FiniCallback = void(void);
  38
  39 static void call_init_array_callbacks(int, char **, char **) {
  40   size_t init_array_size = __init_array_end - __init_array_start;
  41   for (size_t i = 0; i < init_array_size; ++i)
  42     reinterpret_cast<InitCallback *>(__init_array_start[i])();
  43 }
  44
  45 static void call_fini_array_callbacks() {
  46   size_t fini_array_size = __fini_array_end - __fini_array_start;
  47   for (size_t i = fini_array_size; i > 0; --i)
  48     reinterpret_cast<FiniCallback *>(__fini_array_start[i - 1])();
  49 }
  50
  51 } // namespace LIBC_NAMESPACE_DECL
  52
  53 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  54 _begin(int argc, char **argv, char **env) {
  55   __atomic_store_n(&LIBC_NAMESPACE::app.env_ptr,
  56                    reinterpret_cast<uintptr_t *>(env), __ATOMIC_RELAXED);
  57
  58   // We want the fini array callbacks to be run after other atexit
  59   // callbacks are run. So, we register them before running the init
  60   // array callbacks as they can potentially register their own atexit
  61   // callbacks.
  62   LIBC_NAMESPACE::atexit(&LIBC_NAMESPACE::call_fini_array_callbacks);
  63   LIBC_NAMESPACE::call_init_array_callbacks(argc, argv, env);
  64 }
  65
  66 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  67 _start(int argc, char **argv, char **envp, int *ret) {
  68   // Invoke the 'main' function with every active thread that the user launched
  69   // the _start kernel with.
  70   __atomic_fetch_or(ret, main(argc, argv, envp), __ATOMIC_RELAXED);
  71 }
  72
  73 extern "C" [[gnu::visibility("protected"), clang::nvptx_kernel]] void
  74 _end(int retval) {
  75   // To finis the execution we invoke all the callbacks registered via 'atexit'
  76   // and then exit with the appropriate return value.
  77   LIBC_NAMESPACE::exit(retval);
  78 }