[libc-commits] [libc] [libc] Implement temporary `printf` on the GPU (PR #85331)

[Michael Jones via libc-commits]

================
@@ -20,13 +26,139 @@
 #include <vector>
 
 using namespace LIBC_NAMESPACE;
+using namespace LIBC_NAMESPACE::printf_core;
 
 static_assert(sizeof(rpc_buffer_t) == sizeof(rpc::Buffer),
               "Buffer size mismatch");
 
 static_assert(RPC_MAXIMUM_PORT_COUNT == rpc::MAX_PORT_COUNT,
               "Incorrect maximum port count");
 
+template <uint32_t lane_size> void handle_printf(rpc::Server::Port &port) {
+  FILE *files[lane_size] = {nullptr};
+  // Get the appropriate output stream to use.
+  if (port.get_opcode() == RPC_PRINTF_TO_STREAM)
+    port.recv([&](rpc::Buffer *buffer, uint32_t id) {
+      files[id] = reinterpret_cast<FILE *>(buffer->data[0]);
+    });
+  else if (port.get_opcode() == RPC_PRINTF_TO_STDOUT)
+    std::fill(files, files + lane_size, stdout);
+  else
+    std::fill(files, files + lane_size, stderr);
+
+  uint64_t format_sizes[lane_size] = {0};
+  void *format[lane_size] = {nullptr};
+
+  uint64_t args_sizes[lane_size] = {0};
+  void *args[lane_size] = {nullptr};
+
+  // Recieve the format string and arguments from the client.
+  port.recv_n(format, format_sizes,
+              [&](uint64_t size) { return new char[size]; });
+  port.recv_n(args, args_sizes, [&](uint64_t size) { return new char[size]; });
+
+  // Identify any arguments that are actually pointers to strings on the client.
+  // Additionally we want to determine how much buffer space we need to print.
+  std::vector<void *> strs_to_copy[lane_size];
+  int buffer_size[lane_size] = {0};
+  for (uint32_t lane = 0; lane < lane_size; ++lane) {
+    if (!format[lane])
+      continue;
+
+    WriteBuffer wb(nullptr, 0);
+    Writer writer(&wb);
+
+    internal::StructArgList printf_args(args[lane]);
+    Parser<internal::StructArgList> parser(
+        reinterpret_cast<const char *>(format[lane]), printf_args);
+
+    for (FormatSection cur_section = parser.get_next_section();
+         !cur_section.raw_string.empty();
+         cur_section = parser.get_next_section()) {
+      if (cur_section.has_conv && cur_section.conv_name == 's') {
+        strs_to_copy[lane].emplace_back(cur_section.conv_val_ptr);
+      } else if (cur_section.has_conv) {
+        convert(&writer, cur_section);
----------------
michaelrj-google wrote:

If it returns a negative number then you should return that value immediately, if possible. I don't think you'll actually run into any errors (there's a list of error values I've defined at the bottom of `printf_core/core_structs.h`) but if you do then something has gone seriously wrong.

https://github.com/llvm/llvm-project/pull/85331