libc/src/__support/OSUtil/baremetal/io.cpp

   1 //===---------- Baremetal implementation of IO utils ------------*- C++ -*-===//
   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 "io.h"
  10
  11 #include "src/__support/CPP/string_view.h"
  12 #include "src/__support/macros/config.h"
  13
  14 namespace LIBC_NAMESPACE_DECL {
  15
  16 // These are intended to be provided by the vendor.
  17 //
  18 // The signature of these types and functions intentionally match `fopencookie`
  19 // which allows the following:
  20 //
  21 // ```
  22 // struct __llvm_libc_stdio_cookie { ... };
  23 // ...
  24 // struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
  25 // cookie_io_functions_t stdin_func = { .read = __llvm_libc_stdio_read };
  26 // FILE *stdin = fopencookie(&__llvm_libc_stdin_cookie, "r", stdin_func);
  27 // ...
  28 // struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
  29 // cookie_io_functions_t stdout_func = { .write = __llvm_libc_stdio_write };
  30 // FILE *stdout = fopencookie(&__llvm_libc_stdout_cookie, "w", stdout_func);
  31 // ...
  32 // struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
  33 // cookie_io_functions_t stderr_func = { .write = __llvm_libc_stdio_write };
  34 // FILE *stderr = fopencookie(&__llvm_libc_stderr_cookie, "w", stderr_func);
  35 // ```
  36 //
  37 // At the same time, implementation of functions like `printf` and `scanf` can
  38 // use `__llvm_libc_stdio_read` and `__llvm_libc_stdio_write` directly to avoid
  39 // the extra indirection.
  40 //
  41 // All three symbols `__llvm_libc_stdin_cookie`, `__llvm_libc_stdout_cookie`,
  42 // and `__llvm_libc_stderr_cookie` must be provided, even if they don't point
  43 // at anything.
  44
  45 struct __llvm_libc_stdio_cookie;
  46
  47 extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdin_cookie;
  48 extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stdout_cookie;
  49 extern "C" struct __llvm_libc_stdio_cookie __llvm_libc_stderr_cookie;
  50
  51 extern "C" ssize_t __llvm_libc_stdio_read(void *cookie, char *buf, size_t size);
  52 extern "C" ssize_t __llvm_libc_stdio_write(void *cookie, const char *buf,
  53                                            size_t size);
  54
  55 ssize_t read_from_stdin(char *buf, size_t size) {
  56   return __llvm_libc_stdio_read(static_cast<void *>(&__llvm_libc_stdin_cookie),
  57                                 buf, size);
  58 }
  59
  60 void write_to_stdout(cpp::string_view msg) {
  61   __llvm_libc_stdio_write(static_cast<void *>(&__llvm_libc_stdout_cookie),
  62                           msg.data(), msg.size());
  63 }
  64
  65 void write_to_stderr(cpp::string_view msg) {
  66   __llvm_libc_stdio_write(static_cast<void *>(&__llvm_libc_stderr_cookie),
  67                           msg.data(), msg.size());
  68 }
  69
  70 } // namespace LIBC_NAMESPACE_DECL