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 #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
  45 using namespace std;
  46
  47 namespace
  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  */
  55 class PrimaryFiber : public Fiber
  56 {
  57   public:
  58     PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
  59     void main() { panic("PrimaryFiber main executed.\n"); }
  60 };
  61
  62 PrimaryFiber _primaryFiber;
  63
  64 // A pointer to whatever the currently executing Fiber is.
  65 Fiber *_currentFiber = &_primaryFiber;
  66
  67 // A pointer to the Fiber which is currently being started/initialized.
  68 Fiber *startingFiber = nullptr;
  69
  70 } // anonymous namespace
  71
  72 void
  73 Fiber::entryTrampoline()
  74 {
  75     startingFiber->start();
  76 }
  77
  78 Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
  79 {}
  80
  81 Fiber::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
 105 Fiber::~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
 115 void
 116 Fiber::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
 134 void
 135 Fiber::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
 156 void
 157 Fiber::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
 175 Fiber *Fiber::currentFiber() { return _currentFiber; }
 176 Fiber *Fiber::primaryFiber() { return &_primaryFiber; }