fiber.cc revision 14042 
1/*
2 * Copyright 2018 Google, Inc.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are
6 * met: redistributions of source code must retain the above copyright
7 * notice, this list of conditions and the following disclaimer;
8 * redistributions in binary form must reproduce the above copyright
9 * notice, this list of conditions and the following disclaimer in the
10 * documentation and/or other materials provided with the distribution;
11 * neither the name of the copyright holders nor the names of its
12 * contributors may be used to endorse or promote products derived from
13 * this software without specific prior written permission.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
18 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
19 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
21 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
25 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 *
27 * Authors: Gabe Black
28 */
29
30#include "base/fiber.hh"
31
32#if HAVE_VALGRIND
33#include <valgrind/valgrind.h>
34#endif
35
36// Mac OS requires _DARWIN_C_SOURCE if _POSIX_C_SOURCE is defined,
37// otherwise it will mask the definition of MAP_ANONYMOUS.
38// _POSIX_C_SOURCE is already defined by including <ucontext.h> in
39// base/fiber.hh
40#if defined(__APPLE__) && defined(__MACH__)
41#define _DARWIN_C_SOURCE
42#endif
43
44#include <sys/mman.h>
45#include <unistd.h>
46
47#include <cerrno>
48#include <cstdio>
49#include <cstring>
50
51#include "base/logging.hh"
52
53using namespace std;
54
55namespace
56{
57
58/*
59 * The PrimaryFiber class is a special case that attaches to the currently
60 * executing context. That makes handling the "primary" fiber, aka the one
61 * which most of gem5 is running under, no different than other Fibers.
62 */
63class PrimaryFiber : public Fiber
64{
65  public:
66    PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
67    void main() { panic("PrimaryFiber main executed.\n"); }
68};
69
70PrimaryFiber _primaryFiber;
71
72// A pointer to whatever the currently executing Fiber is.
73Fiber *_currentFiber = &_primaryFiber;
74
75// A pointer to the Fiber which is currently being started/initialized.
76Fiber *startingFiber = nullptr;
77
78} // anonymous namespace
79
80void
81Fiber::entryTrampoline()
82{
83    startingFiber->start();
84}
85
86Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
87{}
88
89Fiber::Fiber(Fiber *link, size_t stack_size) :
90    link(link), stack(nullptr), stackSize(stack_size), guardPage(nullptr),
91    guardPageSize(sysconf(_SC_PAGE_SIZE)), _started(false), _finished(false)
92{
93    if (stack_size) {
94        guardPage = mmap(nullptr, guardPageSize + stack_size,
95                         PROT_READ | PROT_WRITE,
96                         MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
97        if (guardPage == (void *)MAP_FAILED) {
98            perror("mmap");
99            fatal("Could not mmap %d byte fiber stack.\n", stack_size);
100        }
101        stack = (void *)((uint8_t *)guardPage + guardPageSize);
102        if (mprotect(guardPage, guardPageSize, PROT_NONE)) {
103            perror("mprotect");
104            fatal("Could not forbid access to fiber stack guard page.");
105        }
106    }
107#if HAVE_VALGRIND
108    valgrindStackId = VALGRIND_STACK_REGISTER(
109            stack, (uint8_t *)stack + stack_size);
110#endif
111}
112
113Fiber::~Fiber()
114{
115    panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
116#if HAVE_VALGRIND
117    VALGRIND_STACK_DEREGISTER(valgrindStackId);
118#endif
119    if (guardPage)
120        munmap(guardPage, guardPageSize + stackSize);
121}
122
123void
124Fiber::createContext()
125{
126    // Set up a context for the new fiber, starting it in the trampoline.
127    getcontext(&ctx);
128    ctx.uc_stack.ss_sp = stack;
129    ctx.uc_stack.ss_size = stackSize;
130    ctx.uc_link = nullptr;
131    makecontext(&ctx, &entryTrampoline, 0);
132
133    // Swap to the new context so it can enter its start() function. It
134    // will then swap itself back out and return here.
135    startingFiber = this;
136    panic_if(!_currentFiber, "No active Fiber object.");
137    swapcontext(&_currentFiber->ctx, &ctx);
138
139    // The new context is now ready and about to call main().
140}
141
142void
143Fiber::start()
144{
145    // Avoid a dangling pointer.
146    startingFiber = nullptr;
147
148    setStarted();
149
150    // Swap back to the parent context which is still considered "current",
151    // now that we're ready to go.
152    int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx);
153    panic_if(ret == -1, strerror(errno));
154
155    // Call main() when we're been reactivated for the first time.
156    main();
157
158    // main has returned, so this Fiber has finished. Switch to the "link"
159    // Fiber.
160    _finished = true;
161    link->run();
162}
163
164void
165Fiber::run()
166{
167    panic_if(_finished, "Fiber has already run to completion.");
168
169    // If we're already running this fiber, we're done.
170    if (_currentFiber == this)
171        return;
172
173    if (!_started)
174        createContext();
175
176    // Switch out of the current Fiber's context and this one's in.
177    Fiber *prev = _currentFiber;
178    Fiber *next = this;
179    _currentFiber = next;
180    swapcontext(&prev->ctx, &next->ctx);
181}
182
183Fiber *Fiber::currentFiber() { return _currentFiber; }
184Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
185