src/sys/socket/linux/recvfrom.cpp

//===-- Linux implementation of recvfrom ----------------------------------===//
//
// 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 "src/sys/socket/recvfrom.h"

#include <linux/net.h>   // For SYS_SOCKET socketcall number.
#include <sys/syscall.h> // For syscall numbers.

#include "hdr/types/socklen_t.h"
#include "hdr/types/ssize_t.h"
#include "hdr/types/struct_sockaddr.h"
#include "src/__support/OSUtil/syscall.h" // For internal syscall function.
#include "src/__support/common.h"
#include "src/__support/libc_errno.h"
#include "src/__support/macros/sanitizer.h"

namespace LIBC_NAMESPACE_DECL {

LLVM_LIBC_FUNCTION(ssize_t, recvfrom,
                   (int sockfd, void *buf, size_t len, int flags,
                    sockaddr *__restrict src_addr,
                    socklen_t *__restrict addrlen)) {
  // addrlen is a value-result argument. If it's not null, it passes the max
  // size of the buffer src_addr to the syscall. After the syscall, it's updated
  // to the actual size of the source address. This may be larger than the
  // buffer, in which case the buffer contains a truncated result.
  size_t srcaddr_sz;
  if (src_addr)
    srcaddr_sz = *addrlen;
  (void)srcaddr_sz; // prevent "set but not used" warning

#ifdef SYS_recvfrom
  ssize_t ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(
      SYS_recvfrom, sockfd, buf, len, flags, src_addr, addrlen);
#elif defined(SYS_socketcall)
  unsigned long sockcall_args[6] = {static_cast<unsigned long>(sockfd),
                                    reinterpret_cast<unsigned long>(buf),
                                    static_cast<unsigned long>(len),
                                    static_cast<unsigned long>(flags),
                                    reinterpret_cast<unsigned long>(src_addr),
                                    static_cast<unsigned long>(addrlen)};
  ssize_t ret = LIBC_NAMESPACE::syscall_impl<ssize_t>(
      SYS_socketcall, SYS_RECVFROM, sockcall_args);
#else
#error "socket and socketcall syscalls unavailable for this platform."
#endif
  if (ret < 0) {
    libc_errno = static_cast<int>(-ret);
    return -1;
  }

  MSAN_UNPOISON(buf, ret);

  if (src_addr) {
    size_t min_src_addr_size = (*addrlen < srcaddr_sz) ? *addrlen : srcaddr_sz;
    (void)min_src_addr_size; // prevent "set but not used" warning

    MSAN_UNPOISON(src_addr, min_src_addr_size);
  }
  return ret;
}

} // namespace LIBC_NAMESPACE_DECL