fiber.cc revision 13435 
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#include <sys/mman.h>
37#include <unistd.h>
38
39#include <cerrno>
40#include <cstdio>
41#include <cstring>
42
43#include "base/logging.hh"
44
45using namespace std;
46
47namespace
48{
49
50/*
51 * The PrimaryFiber class is a special case that attaches to the currently
52 * executing context. That makes handling the "primary" fiber, aka the one
53 * which most of gem5 is running under, no different than other Fibers.
54 */
55class PrimaryFiber : public Fiber
56{
57  public:
58    PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
59    void main() { panic("PrimaryFiber main executed.\n"); }
60};
61
62PrimaryFiber _primaryFiber;
63
64// A pointer to whatever the currently executing Fiber is.
65Fiber *_currentFiber = &_primaryFiber;
66
67// A pointer to the Fiber which is currently being started/initialized.
68Fiber *startingFiber = nullptr;
69
70} // anonymous namespace
71
72void
73Fiber::entryTrampoline()
74{
75    startingFiber->start();
76}
77
78Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
79{}
80
81Fiber::Fiber(Fiber *link, size_t stack_size) :
82    link(link), stack(nullptr), stackSize(stack_size), guardPage(nullptr),
83    guardPageSize(sysconf(_SC_PAGE_SIZE)), started(false), _finished(false)
84{
85    if (stack_size) {
86        guardPage = mmap(nullptr, guardPageSize + stack_size,
87                         PROT_READ | PROT_WRITE,
88                         MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
89        if (guardPage == (void *)MAP_FAILED) {
90            perror("mmap");
91            fatal("Could not mmap %d byte fiber stack.\n", stack_size);
92        }
93        stack = (void *)((uint8_t *)guardPage + guardPageSize);
94        if (mprotect(guardPage, guardPageSize, PROT_NONE)) {
95            perror("mprotect");
96            fatal("Could not forbid access to fiber stack guard page.");
97        }
98    }
99#if HAVE_VALGRIND
100    valgrindStackId = VALGRIND_STACK_REGISTER(
101            stack, (uint8_t *)stack + stack_size);
102#endif
103}
104
105Fiber::~Fiber()
106{
107    panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
108#if HAVE_VALGRIND
109    VALGRIND_STACK_DEREGISTER(valgrindStackId);
110#endif
111    if (guardPage)
112        munmap(guardPage, guardPageSize + stackSize);
113}
114
115void
116Fiber::createContext()
117{
118    // Set up a context for the new fiber, starting it in the trampoline.
119    getcontext(&ctx);
120    ctx.uc_stack.ss_sp = stack;
121    ctx.uc_stack.ss_size = stackSize;
122    ctx.uc_link = nullptr;
123    makecontext(&ctx, &entryTrampoline, 0);
124
125    // Swap to the new context so it can enter its start() function. It
126    // will then swap itself back out and return here.
127    startingFiber = this;
128    panic_if(!_currentFiber, "No active Fiber object.");
129    swapcontext(&_currentFiber->ctx, &ctx);
130
131    // The new context is now ready and about to call main().
132}
133
134void
135Fiber::start()
136{
137    // Avoid a dangling pointer.
138    startingFiber = nullptr;
139
140    setStarted();
141
142    // Swap back to the parent context which is still considered "current",
143    // now that we're ready to go.
144    int ret M5_VAR_USED = swapcontext(&ctx, &_currentFiber->ctx);
145    panic_if(ret == -1, strerror(errno));
146
147    // Call main() when we're been reactivated for the first time.
148    main();
149
150    // main has returned, so this Fiber has finished. Switch to the "link"
151    // Fiber.
152    _finished = true;
153    link->run();
154}
155
156void
157Fiber::run()
158{
159    panic_if(_finished, "Fiber has already run to completion.");
160
161    // If we're already running this fiber, we're done.
162    if (_currentFiber == this)
163        return;
164
165    if (!started)
166        createContext();
167
168    // Switch out of the current Fiber's context and this one's in.
169    Fiber *prev = _currentFiber;
170    Fiber *next = this;
171    _currentFiber = next;
172    swapcontext(&prev->ctx, &next->ctx);
173}
174
175Fiber *Fiber::currentFiber() { return _currentFiber; }
176Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
177