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/*
* Copyright (c) 2003-2005 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Gabe Black
*/
#ifndef __SIM_SYSCALLRETURN_HH__
#define __SIM_SYSCALLRETURN_HH__
#include "base/types.hh"
/**
* This class represents the return value from an emulated system call,
* including any errno setting.
*
* On some platforms, the return value and errno are encoded in a
* single signed integer. A value less than zero but greater than
* -4096 indicates an error, and the value is the negation of the
* errno value. Otherwise, the call was successful and the integer is
* the return value. (Large negative numbers are considered
* successful to allow syscalls to return pointers to high memory,
* e.g., stack addresses.) See, for example, Appendix A of the AMD64
* ABI spec at http://www.x86-64.org/documentation/abi.pdf.
*
* Other platforms use a more complex interface, returning a value and
* an error code in separate registers.
*
* This class is designed to support both types of interfaces.
*/
class SyscallReturn
{
public:
/// For simplicity, allow the object to be initialized with a
/// single signed integer using the same positive=success,
/// negative=-errno convention described above.
///
/// Typically this constructor is used as a default type
/// conversion, so a bare integer is used where a SyscallReturn
/// value is expected, e.g., as the return value from a system
/// call emulation function ('return 0;' or 'return -EFAULT;').
SyscallReturn(int64_t v)
: value(v)
{}
~SyscallReturn() {}
/// Was the system call successful?
bool successful() const
{
return (value >= 0 || value <= -4096);
}
/// The return value
int64_t returnValue() const
{
assert(successful());
return value;
}
/// The errno value
int errnoValue() const
{
assert(!successful());
return -value;
}
/// The encoded value (as described above)
int64_t encodedValue() const
{
return value;
}
private:
int64_t value;
};
#endif
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