[libc] Use string_view for write_to_stderr

[gchatelet]

Summary

This patch makes use of cpp::string_view instead of const char* for write_to_stderr. This helps sending non null-terminated buffers such as a single character, cpp::string_view or cpp::string.
It also fizes the gpu version that had several bugs (See https://reviews.llvm.org/D145913#4236641).

[gchatelet]

• Always send null-terminated string so we can use fputs on the server side

[jhuber6]

Do we want to stop using const char *? We only use this internally currently, but it was easier for me to test when it was a C type. I'll let @sivachandra decide.

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

22

26

Does libc not use C++ style casts?

[gchatelet]

In D147375#4238339, @jhuber6 wrote:

Do we want to stop using const char *? We only use this internally currently, but it was easier for me to test when it was a C type. I'll let @sivachandra decide.

cpp::string_view is implicitly constructible from a const char* so the current code still works. Are you calling the function from C code?
Relevant discussion for this patch: https://reviews.llvm.org/D147231#inline-1423241

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

22

Thx for catching the typo!

[gchatelet]

• Address comments

[jhuber6]

In D147375#4238363, @gchatelet wrote:

In D147375#4238339, @jhuber6 wrote:

Do we want to stop using const char *? We only use this internally currently, but it was easier for me to test when it was a C type. I'll let @sivachandra decide.

cpp::string_view is implicitly constructible from a const char* so the current code still works. Are you calling the function from C code?
Relevant discussion for this patch: https://reviews.llvm.org/D147231#inline-1423241

I was just calling it using this function for a standalone test, but it's not a huge deal. Alternatively, we could keep the function interface the same and do the conversion internally.

namespace __llvm_libc {
void write_to_stderr(const char *msg);
void quick_exit(int);
} // namespace __llvm_libc

[sivachandra]

OK for linux/io.h.

[gchatelet]

• Keep "const char*" version for gpu/io.h

[gchatelet]

In D147375#4238384, @jhuber6 wrote:

In D147375#4238363, @gchatelet wrote:

In D147375#4238339, @jhuber6 wrote:

Do we want to stop using const char *? We only use this internally currently, but it was easier for me to test when it was a C type. I'll let @sivachandra decide.

cpp::string_view is implicitly constructible from a const char* so the current code still works. Are you calling the function from C code?
Relevant discussion for this patch: https://reviews.llvm.org/D147231#inline-1423241

I was just calling it using this function for a standalone test, but it's not a huge deal.

I can keep the const char* version in the gpu folder on top of the string_view version if that helps.

Alternatively, we could keep the function interface the same and do the conversion internally.

This wouldn't help for single char or non null-terminated strings.

[jhuber6]

That's fine, we can always change things later.

libc/src/__support/OSUtil/gpu/CMakeLists.txt

 add_object_library(
   gpu_util
   SRCS
     quick_exit.cpp
     io.cpp
   HDRS
     quick_exit.h
     io.h
   DEPENDS
     libc.src.__support.common
+    libc.src.__support.CPP.string_view
     libc.src.__support.RPC.rpc_client
+    libc.src.string.memory_utils.memcpy_implementation
 )

libc/src/__support/OSUtil/gpu/io.h

 //===-------------- GPU implementation of IO utils --------------*- C++ -*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_SUPPORT_OSUTIL_GPU_IO_H
 #define LLVM_LIBC_SRC_SUPPORT_OSUTIL_GPU_IO_H
 
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/macros/attributes.h" // LIBC_INLINE
+
 namespace __llvm_libc {
 
-void write_to_stderr(const char *msg);
+void write_to_stderr(cpp::string_view msg);
+
+LIBC_INLINE void write_to_stderr(const char *msg) {
+  write_to_stderr(cpp::string_view(msg));
+}
 
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SUPPORT_OSUTIL_LINUX_IO_H

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

 //===-------------- GPU implementation of IO utils --------------*- C++ -*-===//
 //
 // 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 "io.h"
 
+#include "src/__support/CPP/string_view.h"
 #include "src/__support/RPC/rpc_client.h"
-#include "src/string/string_utils.h"
+#include "src/string/memory_utils/memcpy_implementations.h"
 
 namespace __llvm_libc {
 
-void write_to_stderr(const char *msg) {
-  uint64_t length = internal::string_length(msg) + 1;
-  uint64_t buffer_len = sizeof(rpc::Buffer) - sizeof(uint64_t);
-  for (uint64_t i = 0; i < length; i += buffer_len) {
-    rpc::client.run(
-        [&](rpc::Buffer *buffer) {
-          buffer->data[0] = rpc::Opcode::PRINT_TO_STDERR;
-          inline_memcpy(reinterpret_cast<char *>(&buffer->data[1]), &msg[i],
-                        (length > buffer_len ? buffer_len : length));
-        },
-        [](rpc::Buffer *) { /* void */ });
-  }
+namespace internal {
+
+static constexpr size_t BUFFER_SIZE = sizeof(rpc::Buffer) - sizeof(uint64_t);
+static constexpr size_t MAX_STRING_SIZE = BUFFER_SIZE;
+
+LIBC_INLINE void send_null_terminated(cpp::string_view src) {
+        char *data = reinterpret_cast<char *>(&buffer->data[1]);
+        inline_memcpy(data, src.data(), src.size());
+        data[src.size()] = '\0';
+
+} // namespace internal
+
+void write_to_stderr(cpp::string_view msg) {
+  bool send_empty_string = true;
+  for (; !msg.empty();) {
+    const auto chunk = msg.substr(0, internal::MAX_STRING_SIZE);
+    internal::send_null_terminated(chunk);
+    msg.remove_prefix(chunk.size());
+    send_empty_string = false;
+  }
+  if (send_empty_string)
+    internal::send_null_terminated("");
 }
 
 } // namespace __llvm_libc

libc/src/__support/OSUtil/linux/CMakeLists.txt

 if(NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_ARCHITECTURE})
   return()
 endif()
 
 add_subdirectory(${LIBC_TARGET_ARCHITECTURE})
 
 add_header_library(
   linux_util
   HDRS
     io.h
     quick_exit.h
     syscall.h
   DEPENDS
     .${LIBC_TARGET_ARCHITECTURE}.linux_${LIBC_TARGET_ARCHITECTURE}_util
     libc.src.__support.common
+    libc.src.__support.CPP.string_view
 )

libc/src/__support/OSUtil/linux/io.h

 //===-------------- Linux implementation of IO utils ------------*- C++ -*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_SRC_SUPPORT_OSUTIL_LINUX_IO_H
 #define LLVM_LIBC_SRC_SUPPORT_OSUTIL_LINUX_IO_H
 
-#include "src/string/string_utils.h"
+#include "src/__support/CPP/string_view.h"
 #include "syscall.h" // For internal syscall function.
 
 #include <sys/syscall.h> // For syscall numbers.
 
 namespace __llvm_libc {
 
-LIBC_INLINE void write_to_stderr(const char *msg) {
-  __llvm_libc::syscall_impl(SYS_write, 2 /* stderr */, msg,
-                            internal::string_length(msg));
+LIBC_INLINE void write_to_stderr(cpp::string_view msg) {
+  __llvm_libc::syscall_impl(SYS_write, 2 /* stderr */, msg.data(), msg.size());
 }
 
 } // namespace __llvm_libc
 
 #endif // LLVM_LIBC_SRC_SUPPORT_OSUTIL_LINUX_IO_H