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/*
* Copyright 2018 Google, Inc.
*
* 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
*/
#include "base/fiber.hh"
#if HAVE_VALGRIND
#include <valgrind/valgrind.h>
#endif
// Mac OS requires _DARWIN_C_SOURCE if _POSIX_C_SOURCE is defined,
// otherwise it will mask the definition of MAP_ANONYMOUS.
// _POSIX_C_SOURCE is already defined by including <ucontext.h> in
// base/fiber.hh
#if defined(__APPLE__) && defined(__MACH__)
#define _DARWIN_C_SOURCE
#endif
#include <sys/mman.h>
#include <unistd.h>
#include <cerrno>
#include <cstdio>
#include <cstring>
#include "base/logging.hh"
using namespace std;
namespace
{
/*
* The PrimaryFiber class is a special case that attaches to the currently
* executing context. That makes handling the "primary" fiber, aka the one
* which most of gem5 is running under, no different than other Fibers.
*/
class PrimaryFiber : public Fiber
{
public:
PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
void main() { panic("PrimaryFiber main executed.\n"); }
};
PrimaryFiber _primaryFiber;
// A pointer to whatever the currently executing Fiber is.
Fiber *_currentFiber = &_primaryFiber;
// A pointer to the Fiber which is currently being started/initialized.
Fiber *startingFiber = nullptr;
} // anonymous namespace
void
Fiber::entryTrampoline()
{
startingFiber->start();
}
Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
{}
Fiber::Fiber(Fiber *link, size_t stack_size) :
link(link), stack(nullptr), stackSize(stack_size), guardPage(nullptr),
guardPageSize(sysconf(_SC_PAGE_SIZE)), _started(false), _finished(false)
{
if (stack_size) {
guardPage = mmap(nullptr, guardPageSize + stack_size,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (guardPage == (void *)MAP_FAILED) {
perror("mmap");
fatal("Could not mmap %d byte fiber stack.\n", stack_size);
}
stack = (void *)((uint8_t *)guardPage + guardPageSize);
if (mprotect(guardPage, guardPageSize, PROT_NONE)) {
perror("mprotect");
fatal("Could not forbid access to fiber stack guard page.");
}
}
#if HAVE_VALGRIND
valgrindStackId = VALGRIND_STACK_REGISTER(
stack, (uint8_t *)stack + stack_size);
#endif
}
Fiber::~Fiber()
{
panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
#if HAVE_VALGRIND
VALGRIND_STACK_DEREGISTER(valgrindStackId);
#endif
if (guardPage)
munmap(guardPage, guardPageSize + stackSize);
}
void
Fiber::createContext()
{
// Set up a context for the new fiber, starting it in the trampoline.
getcontext(&ctx);
ctx.uc_stack.ss_sp = stack;
ctx.uc_stack.ss_size = stackSize;
ctx.uc_link = nullptr;
makecontext(&ctx, &entryTrampoline, 0);
// Swap to the new context so it can enter its start() function. It
// will then swap itself back out and return here.
startingFiber = this;
panic_if(!_currentFiber, "No active Fiber object.");
swapcontext(&_currentFiber->ctx, &ctx);
// The new context is now ready and about to call main().
}
void
Fiber::start()
{
// Avoid a dangling pointer.
startingFiber = nullptr;
setStarted();
// Swap back to the parent context which is still considered "current",
// now that we're ready to go.
int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx);
panic_if(ret == -1, strerror(errno));
// Call main() when we're been reactivated for the first time.
main();
// main has returned, so this Fiber has finished. Switch to the "link"
// Fiber.
_finished = true;
link->run();
}
void
Fiber::run()
{
panic_if(_finished, "Fiber has already run to completion.");
// If we're already running this fiber, we're done.
if (_currentFiber == this)
return;
if (!_started)
createContext();
// Switch out of the current Fiber's context and this one's in.
Fiber *prev = _currentFiber;
Fiber *next = this;
_currentFiber = next;
swapcontext(&prev->ctx, &next->ctx);
}
Fiber *Fiber::currentFiber() { return _currentFiber; }
Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
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