src/base/fiber.cc

   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
  53 using namespace std;
  54
  55 namespace
  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  */
  63 class PrimaryFiber : public Fiber
  64 {
  65   public:
  66     PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
  67     void main() { panic("PrimaryFiber main executed.\n"); }
  68 };
  69
  70 PrimaryFiber _primaryFiber;
  71
  72 // A pointer to whatever the currently executing Fiber is.
  73 Fiber *_currentFiber = &_primaryFiber;
  74
  75 // A pointer to the Fiber which is currently being started/initialized.
  76 Fiber *startingFiber = nullptr;
  77
  78 } // anonymous namespace
  79
  80 void
  81 Fiber::entryTrampoline()
  82 {
  83     startingFiber->start();
  84 }
  85
  86 Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
  87 {}
  88
  89 Fiber::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
 113 Fiber::~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
 123 void
 124 Fiber::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
 142 void
 143 Fiber::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
 164 void
 165 Fiber::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
 183 Fiber *Fiber::currentFiber() { return _currentFiber; }
 184 Fiber *Fiber::primaryFiber() { return &_primaryFiber; }