libc/src/__support/arg_list.h

//===-- Holder Class for manipulating va_lists ------------------*- 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_ARG_LIST_H
#define LLVM_LIBC_SRC___SUPPORT_ARG_LIST_H

#include "src/__support/common.h"
#include "src/__support/macros/config.h"

#include <stdarg.h>
#include <stddef.h>
#include <stdint.h>

namespace LIBC_NAMESPACE_DECL {
namespace internal {

template <typename V, typename A>
LIBC_INLINE constexpr V align_up(V val, A align) {
  return ((val + V(align) - 1) / V(align)) * V(align);
}

class ArgList {
  va_list vlist;

public:
  LIBC_INLINE ArgList(va_list vlist) { va_copy(this->vlist, vlist); }
  LIBC_INLINE ArgList(ArgList &other) { va_copy(this->vlist, other.vlist); }
  LIBC_INLINE ~ArgList() { va_end(this->vlist); }

  LIBC_INLINE ArgList &operator=(ArgList &rhs) {
    va_copy(vlist, rhs.vlist);
    return *this;
  }

  template <class T> LIBC_INLINE T next_var() { return va_arg(vlist, T); }
};

// Used for testing things that use an ArgList when it's impossible to know what
// the arguments should be ahead of time. An example of this would be fuzzing,
// since a function passed a random input could request unpredictable arguments.
class MockArgList {
  size_t arg_counter = 0;

public:
  LIBC_INLINE MockArgList() = default;
  LIBC_INLINE MockArgList(va_list) { ; }
  LIBC_INLINE MockArgList(MockArgList &other) {
    arg_counter = other.arg_counter;
  }
  LIBC_INLINE ~MockArgList() = default;

  LIBC_INLINE MockArgList &operator=(MockArgList &rhs) {
    arg_counter = rhs.arg_counter;
    return *this;
  }

  template <class T> LIBC_INLINE T next_var() {
    arg_counter++;
    return T(arg_counter);
  }

  size_t read_count() const { return arg_counter; }
};

// Used by the GPU implementation to parse how many bytes need to be read from
// the variadic argument buffer.
template <bool packed> class DummyArgList {
  size_t arg_counter = 0;

public:
  LIBC_INLINE DummyArgList() = default;
  LIBC_INLINE DummyArgList(va_list) { ; }
  LIBC_INLINE DummyArgList(DummyArgList &other) {
    arg_counter = other.arg_counter;
  }
  LIBC_INLINE ~DummyArgList() = default;

  LIBC_INLINE DummyArgList &operator=(DummyArgList &rhs) {
    arg_counter = rhs.arg_counter;
    return *this;
  }

  template <class T> LIBC_INLINE T next_var() {
    arg_counter = packed ? arg_counter + sizeof(T)
                         : align_up(arg_counter, alignof(T)) + sizeof(T);
    return T(arg_counter);
  }

  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.
template <bool packed> 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() {
    if (!packed)
      ptr = reinterpret_cast<void *>(
          align_up(reinterpret_cast<uintptr_t>(ptr), alignof(T)));
    if (ptr >= end)
      return T(-1);

    // Memcpy because pointer alignment may be illegal given a packed struct.
    T val;
    __builtin_memcpy(&val, ptr, sizeof(T));

    ptr =
        reinterpret_cast<void *>(reinterpret_cast<uintptr_t>(ptr) + sizeof(T));
    return val;
  }
};

} // namespace internal
} // namespace LIBC_NAMESPACE_DECL

#endif // LLVM_LIBC_SRC___SUPPORT_ARG_LIST_H