[libc] Implement temporary printf on the GPU

libc/config/gpu/entrypoints.txt

@@ -211,6 +211,7 @@ set(TARGET_LIBC_ENTRYPOINTS
 
     # gpu/rpc.h entrypoints
     libc.src.gpu.rpc_host_call
+    libc.src.gpu.rpc_fprintf
 )
 
 set(TARGET_LIBM_ENTRYPOINTS

libc/include/llvm-libc-types/rpc_opcodes_t.h

@@ -31,6 +31,9 @@ typedef enum {
   RPC_FTELL,
   RPC_FFLUSH,
   RPC_UNGETC,
+  RPC_PRINTF_TO_STDOUT,
+  RPC_PRINTF_TO_STDERR,
+  RPC_PRINTF_TO_STREAM,
   RPC_LAST = 0xFFFF,
 } rpc_opcode_t;
 

libc/spec/gpu_ext.td

@@ -10,6 +10,14 @@ def GPUExtensions : StandardSpec<"GPUExtensions"> {
             RetValSpec<VoidType>,
             [ArgSpec<VoidPtr>, ArgSpec<VoidPtr>, ArgSpec<SizeTType>]
         >,
+        FunctionSpec<
+            "rpc_fprintf",
+            RetValSpec<IntType>,
+            [ArgSpec<FILERestrictedPtr>,
+             ArgSpec<ConstCharRestrictedPtr>,
+             ArgSpec<VoidPtr>,
+             ArgSpec<SizeTType>]
+        >,
     ]
   >;
   let Headers = [

libc/src/__support/arg_list.h

@@ -13,6 +13,7 @@
 
 #include <stdarg.h>
 #include <stddef.h>
+#include <stdint.h>
 
 namespace LIBC_NAMESPACE {
 namespace internal {
@@ -60,6 +61,43 @@ class MockArgList {
   size_t read_count() const { return arg_counter; }
 };
 
+// Used for the GPU implementation of `printf`. This models a variadic list as a
+// simple array of pointers that are built manually by the implementation.
+class StructArgList {
+  void *ptr;
+  void *end;
+
+public:
+  LIBC_INLINE StructArgList(void *ptr, size_t size)
+      : ptr(ptr), end(reinterpret_cast<unsigned char *>(ptr) + size) {}
+  LIBC_INLINE StructArgList(const StructArgList &other) {
+    ptr = other.ptr;
+    end = other.end;
+  }
+  LIBC_INLINE StructArgList() = default;
+  LIBC_INLINE ~StructArgList() = default;
+
+  LIBC_INLINE StructArgList &operator=(const StructArgList &rhs) {
+    ptr = rhs.ptr;
+    return *this;
+  }
+
+  LIBC_INLINE void *get_ptr() const { return ptr; }
+
+  template <class T> LIBC_INLINE T next_var() {
+    ptr = reinterpret_cast<void *>(
+        ((reinterpret_cast<uintptr_t>(ptr) + alignof(T) - 1) / alignof(T)) *
+        alignof(T));
+
+    if (ptr >= end)
+      return T(-1);
+
+    T val = *reinterpret_cast<T *>(ptr);
+    ptr = reinterpret_cast<unsigned char *>(ptr) + sizeof(T);
+    return val;
+  }
+};
+
 } // namespace internal
 } // namespace LIBC_NAMESPACE
 

libc/src/gpu/CMakeLists.txt

@@ -8,3 +8,15 @@ add_entrypoint_object(
     libc.src.__support.RPC.rpc_client
     libc.src.__support.GPU.utils
 )
+
+add_entrypoint_object(
+  rpc_fprintf
+  SRCS
+    rpc_fprintf.cpp
+  HDRS
+    rpc_fprintf.h
+  DEPENDS
+    libc.src.stdio.gpu.gpu_file
+    libc.src.__support.RPC.rpc_client
+    libc.src.__support.GPU.utils
+)

libc/src/gpu/rpc_fprintf.cpp

@@ -0,0 +1,71 @@
+//===-- GPU implementation of fprintf -------------------------------------===//
+//
+// 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 "rpc_fprintf.h"
+
+#include "src/__support/CPP/string_view.h"
+#include "src/__support/GPU/utils.h"
+#include "src/__support/RPC/rpc_client.h"
+#include "src/__support/common.h"
+#include "src/stdio/gpu/file.h"
+
+namespace LIBC_NAMESPACE {
+
+template <uint16_t opcode>
+int fprintf_impl(::FILE *__restrict file, const char *__restrict format,
+                 size_t format_size, void *args, size_t args_size) {
+  uint64_t mask = gpu::get_lane_mask();
+  rpc::Client::Port port = rpc::client.open<opcode>();
+
+  if constexpr (opcode == RPC_PRINTF_TO_STREAM) {
+    port.send([&](rpc::Buffer *buffer) {
+      buffer->data[0] = reinterpret_cast<uintptr_t>(file);
+    });
+  }
+
+  port.send_n(format, format_size);
+  port.send_n(args, args_size);
+
+  uint32_t ret = 0;
+  for (;;) {
+    const char *str = nullptr;
+    port.recv([&](rpc::Buffer *buffer) {
+      ret = static_cast<uint32_t>(buffer->data[0]);
+      str = reinterpret_cast<const char *>(buffer->data[1]);
+    });
+    // If any lanes have a string argument it needs to be copied back.
+    if (!gpu::ballot(mask, str))
+      break;
+
+    uint64_t size = str ? internal::string_length(str) + 1 : 0;
+    port.send_n(str, size);
+  }
+
+  port.close();
+  return ret;
+}
+
+// TODO: This is a stand-in function that uses a struct pointer and size in
+// place of varargs. Once varargs support is added we will use that to
+// implement the real version.
+LLVM_LIBC_FUNCTION(int, rpc_fprintf,
+                   (::FILE *__restrict stream, const char *__restrict format,
+                    void *args, size_t size)) {
+  cpp::string_view str(format);
+  if (stream == stdout)
+    return fprintf_impl<RPC_PRINTF_TO_STDOUT>(stream, format, str.size() + 1,
+                                              args, size);
+  else if (stream == stderr)
+    return fprintf_impl<RPC_PRINTF_TO_STDERR>(stream, format, str.size() + 1,
+                                              args, size);
+  else
+    return fprintf_impl<RPC_PRINTF_TO_STREAM>(stream, format, str.size() + 1,
+                                              args, size);
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/gpu/rpc_fprintf.h

@@ -0,0 +1,22 @@
+//===-- Implementation header for RPC functions -----------------*- 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_GPU_RPC_HOST_CALL_H
+#define LLVM_LIBC_SRC_GPU_RPC_HOST_CALL_H
+
+#include <stddef.h>
+#include <stdio.h>
+
+namespace LIBC_NAMESPACE {
+
+int rpc_fprintf(::FILE *__restrict stream, const char *__restrict format,
+                void *argc, size_t size);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_GPU_RPC_HOST_CALL_H

libc/test/integration/src/stdio/CMakeLists.txt

@@ -1,3 +1,6 @@
+if(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${LIBC_TARGET_OS})
+  add_subdirectory(${LIBC_TARGET_OS})
+endif()
 add_custom_target(stdio-integration-tests)
 add_dependencies(libc-integration-tests stdio-integration-tests)
 

libc/test/integration/src/stdio/gpu/CMakeLists.txt

@@ -0,0 +1,21 @@
+add_custom_target(stdio-gpu-integration-tests)
+add_dependencies(libc-integration-tests stdio-gpu-integration-tests)
+
+# Create an output directory for any temporary test files.
+file(MAKE_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/testdata)
+
+# These tests are not for correctness testing, but are instead a convenient way
+# to generate hermetic binaries for comparitive binary size testing.
+add_integration_test(
+  printf_test
+  SUITE
+    stdio-gpu-integration-tests
+  SRCS
+    printf.cpp
+  DEPENDS
+    libc.src.gpu.rpc_fprintf
+    libc.src.stdio.fopen
+  LOADER_ARGS
+    --threads 32
+    --blocks 4
+)

libc/test/integration/src/stdio/gpu/printf.cpp

@@ -0,0 +1,88 @@
+//===-- RPC test to check args to printf ----------------------------------===//
+//
+// 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 "test/IntegrationTest/test.h"
+
+#include "src/__support/GPU/utils.h"
+#include "src/gpu/rpc_fprintf.h"
+#include "src/stdio/fopen.h"
+
+using namespace LIBC_NAMESPACE;
+
+FILE *file = LIBC_NAMESPACE::fopen("testdata/test_data.txt", "w");
+
+TEST_MAIN(int argc, char **argv, char **envp) {
+  ASSERT_TRUE(file && "failed to open file");
+  // Check basic printing.
+  int written = 0;
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "A simple string\n", nullptr, 0);
+  ASSERT_EQ(written, 16);
+
+  const char *str = "A simple string\n";
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%s", &str, sizeof(void *));
+  ASSERT_EQ(written, 16);
+
+  // Check printing a different value with each thread.
+  uint64_t thread_id = gpu::get_thread_id();
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%8ld\n", &thread_id,
+                                        sizeof(thread_id));
+  ASSERT_EQ(written, 9);
+
+  struct {
+    uint32_t x = 1;
+    char c = 'c';
+    double f = 1.0;
+  } args1;
+  written =
+      LIBC_NAMESPACE::rpc_fprintf(file, "%d%c%.1f\n", &args1, sizeof(args1));
+  ASSERT_EQ(written, 6);
+
+  struct {
+    uint32_t x = 1;
+    const char *str = "A simple string\n";
+  } args2;
+  written =
+      LIBC_NAMESPACE::rpc_fprintf(file, "%032b%s\n", &args2, sizeof(args2));
+  ASSERT_EQ(written, 49);
+
+  // Check that the server correctly handles divergent numbers of arguments.
+  const char *format = gpu::get_thread_id() % 2 ? "%s" : "%20ld\n";
+  written = LIBC_NAMESPACE::rpc_fprintf(file, format, &str, sizeof(void *));
+  ASSERT_EQ(written, gpu::get_thread_id() % 2 ? 16 : 21);
+
+  format = gpu::get_thread_id() % 2 ? "%s" : str;
+  written = LIBC_NAMESPACE::rpc_fprintf(file, format, &str, sizeof(void *));
+  ASSERT_EQ(written, 16);
+
+  // Check that we handle null arguments correctly.
+  struct {
+    void *null = nullptr;
+  } args3;
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%p", &args3, sizeof(args3));
+  ASSERT_EQ(written, 9);
+
+#ifndef LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%s", &args3, sizeof(args3));
+  ASSERT_EQ(written, 6);
+#endif // LIBC_COPT_PRINTF_NO_NULLPTR_CHECKS
+
+  // Check for extremely abused variable width arguments
+  struct {
+    uint32_t x = 1;
+    uint32_t y = 2;
+    double f = 1.0;
+  } args4;
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%**d", &args4, sizeof(args4));
+  ASSERT_EQ(written, 4);
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%**d%6d", &args4, sizeof(args4));
+  ASSERT_EQ(written, 10);
+  written = LIBC_NAMESPACE::rpc_fprintf(file, "%**.**f", &args4, sizeof(args4));
+  ASSERT_EQ(written, 7);
+
+  return 0;
+}

libc/utils/gpu/server/CMakeLists.txt

@@ -1,4 +1,8 @@
-add_library(llvmlibc_rpc_server STATIC rpc_server.cpp)
+add_library(llvmlibc_rpc_server STATIC
+  ${LIBC_SOURCE_DIR}/src/stdio/printf_core/writer.cpp
+  ${LIBC_SOURCE_DIR}/src/stdio/printf_core/converter.cpp
+  rpc_server.cpp
+)
 
 # Include the RPC implemenation from libc.
 target_include_directories(llvmlibc_rpc_server PRIVATE ${LIBC_SOURCE_DIR})
@@ -9,6 +13,10 @@ target_include_directories(llvmlibc_rpc_server PUBLIC ${CMAKE_CURRENT_SOURCE_DIR
 target_compile_options(llvmlibc_rpc_server PUBLIC
                        $<$<CXX_COMPILER_ID:GNU>:-Wno-attributes>)
 target_compile_definitions(llvmlibc_rpc_server PUBLIC
+                           LIBC_COPT_USE_C_ASSERT
+                           LIBC_COPT_ARRAY_ARG_LIST
+                           LIBC_COPT_PRINTF_DISABLE_WRITE_INT
+                           LIBC_COPT_PRINTF_DISABLE_INDEX_MODE
                            LIBC_NAMESPACE=${LIBC_NAMESPACE})
 
 # Install the server and associated header.