[libc] Fix printing on the GPU when given a `cpp::string_ref`

[jhuber6]

Summary

The implementation of the test printing currently expects a null
terminated C-string. However, the write_to_stderr interface uses a
string view, which doesn't need to be null terminated. This patch
changes the printing interface to directly use fwrite instead rather
than relying on a null terminator.

[sivachandra]

libc/utils/gpu/loader/Server.h

37

Why not new and delete?

[jhuber6]

libc/utils/gpu/loader/Server.h

37

Good point, just more used to using malloc and free. I'll change it before landing.

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

 #include "src/__support/CPP/string_view.h"
 #include "src/__support/RPC/rpc_client.h"
 #include "src/string/memory_utils/memcpy_implementations.h"
 
 namespace __llvm_libc {
 
 void write_to_stderr(cpp::string_view msg) {
   rpc::Port port = rpc::client.open(rpc::PRINT_TO_STDERR);
-  port.send_n(msg.data(), msg.size() + 1);
+  port.send_n(msg.data(), msg.size());
   port.close();
 }
 
 } // namespace __llvm_libc

libc/utils/gpu/loader/Server.h

 /// are any active requests.
 void handle_server() {
   auto port = server.try_open();
   if (!port)
     return;
 
   switch (port->get_opcode()) {
   case __llvm_libc::rpc::Opcode::PRINT_TO_STDERR: {
+    uint64_t str_size;
     void *str = nullptr;
-    port->recv_n([&](uint64_t size) { return str = malloc(size); });
-    fputs(reinterpret_cast<char *>(str), stderr);
+    port->recv_n([&](uint64_t size) {
+      str_size = size;
+      str = malloc(size);
+      return str;
+    });
+    fwrite(str, str_size, 1, stderr);
     free(str);
     break;
   }
   case __llvm_libc::rpc::Opcode::EXIT: {
     port->recv([](__llvm_libc::rpc::Buffer *buffer) {
       exit(reinterpret_cast<uint32_t *>(buffer->data)[0]);
     });
     break;