[libc] Rework the file handling for the GPU

The GPU has much tighter requirements for handling IO functions.
Previously we attempted to define the GPU as one of the platform files.
Using a common interface allowed us to easily define these functions
without much extra work. However, it became more clear that this was a
poor fit for the GPU. The file interface uses function pointers, which
prevented inlining and caused bad perfromance and resource usage on the
GPU. Further, using an actual `FILE` type rather than referring to it as
a host stub prevented us from usin files coming from the host on the GPU
device.

After talking with @sivachandra, the approach now is to simply define
GPU specific versions of the functions we intend to support. Also, we
are ignoring `errno` for the time being as it is unlikely we will ever
care about supporting it fully.

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D157427

1 files changed, 16 insertions, 0 deletions

diff --git a/libc/src/stdio/gpu/stdout.cpp b/libc/src/stdio/gpu/stdout.cpp
new file mode 100644
index 0000000..02425d3
--- /dev/null
+++ b/libc/src/stdio/gpu/stdout.cpp
@@ -0,0 +1,16 @@
+//===-- Definition of the global stdout object ----------------------------===//
+//
+// 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 <stdio.h>
+
+namespace __llvm_libc {
+static struct {
+} stub;
+FILE *stdout = reinterpret_cast<FILE *>(&stub);
+} // namespace __llvm_libc
+extern "C" FILE *stdout = reinterpret_cast<FILE *>(&__llvm_libc::stub);