gem5  v21.1.0.2
fiber.cc
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27 
28 #include "base/fiber.hh"
29 
30 #if HAVE_VALGRIND
31 #include <valgrind/valgrind.h>
32 #endif
33 
34 // Mac OS requires _DARWIN_C_SOURCE if _POSIX_C_SOURCE is defined,
35 // otherwise it will mask the definition of MAP_ANONYMOUS.
36 // _POSIX_C_SOURCE is already defined by including <ucontext.h> in
37 // base/fiber.hh
38 #if defined(__APPLE__) && defined(__MACH__)
39 #define _DARWIN_C_SOURCE
40 #endif
41 
42 #include <sys/mman.h>
43 #include <unistd.h>
44 
45 #include <cerrno>
46 #include <cstdio>
47 #include <cstring>
48 
49 #include "base/logging.hh"
50 
51 namespace gem5
52 {
53 
54 namespace
55 {
56 
57 /*
58  * The PrimaryFiber class is a special case that attaches to the currently
59  * executing context. That makes handling the "primary" fiber, aka the one
60  * which most of gem5 is running under, no different than other Fibers.
61  */
62 class PrimaryFiber : public Fiber
63 {
64  public:
65  PrimaryFiber() : Fiber(nullptr, 0) { setStarted(); }
66  void main() { panic("PrimaryFiber main executed.\n"); }
67 };
68 
69 PrimaryFiber _primaryFiber;
70 
71 // A pointer to whatever the currently executing Fiber is.
72 Fiber *_currentFiber = &_primaryFiber;
73 
74 // A pointer to the Fiber which is currently being started/initialized.
75 Fiber *startingFiber = nullptr;
76 
77 } // anonymous namespace
78 
79 void
81 {
82  startingFiber->start();
83 }
84 
85 Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
86 {}
87 
88 Fiber::Fiber(Fiber *link, size_t stack_size) :
89  link(link), stack(nullptr), stackSize(stack_size), guardPage(nullptr),
90  guardPageSize(sysconf(_SC_PAGE_SIZE)), _started(false), _finished(false)
91 {
92  if (stack_size) {
93  guardPage = mmap(nullptr, guardPageSize + stack_size,
94  PROT_READ | PROT_WRITE,
95  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
96  if (guardPage == (void *)MAP_FAILED) {
97  perror("mmap");
98  fatal("Could not mmap %d byte fiber stack.\n", stack_size);
99  }
100  stack = (void *)((uint8_t *)guardPage + guardPageSize);
101  if (mprotect(guardPage, guardPageSize, PROT_NONE)) {
102  perror("mprotect");
103  fatal("Could not forbid access to fiber stack guard page.");
104  }
105  }
106 #if HAVE_VALGRIND
107  valgrindStackId = VALGRIND_STACK_REGISTER(
108  stack, (uint8_t *)stack + stack_size);
109 #endif
110 }
111 
113 {
114  panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
115 #if HAVE_VALGRIND
116  VALGRIND_STACK_DEREGISTER(valgrindStackId);
117 #endif
118  if (guardPage)
119  munmap(guardPage, guardPageSize + stackSize);
120 }
121 
122 void
124 {
125  // Set up a context for the new fiber, starting it in the trampoline.
126  getcontext(&ctx);
127  ctx.uc_stack.ss_sp = stack;
128  ctx.uc_stack.ss_size = stackSize;
129  ctx.uc_link = nullptr;
130  makecontext(&ctx, &entryTrampoline, 0);
131 
132  // Swap to the new context so it can enter its start() function. It
133  // will then swap itself back out and return here.
134  startingFiber = this;
135  panic_if(!_currentFiber, "No active Fiber object.");
136  swapcontext(&_currentFiber->ctx, &ctx);
137 
138  // The new context is now ready and about to call main().
139 }
140 
141 void
143 {
144  // Avoid a dangling pointer.
145  startingFiber = nullptr;
146 
147  setStarted();
148 
149  if (_setjmp(jmp) == 0) {
150  // Swap back to the parent context which is still considered "current",
151  // now that we're ready to go.
152  int ret = swapcontext(&ctx, &_currentFiber->ctx);
153  panic_if(ret == -1, strerror(errno));
154  }
155 
156  // Call main() when we're been reactivated for the first time.
157  main();
158 
159  // main has returned, so this Fiber has finished. Switch to the "link"
160  // Fiber.
161  _finished = true;
162  link->run();
163 }
164 
165 void
167 {
168  panic_if(_finished, "Fiber has already run to completion.");
169 
170  // If we're already running this fiber, we're done.
171  if (_currentFiber == this)
172  return;
173 
174  if (!_started)
175  createContext();
176 
177  // Switch out of the current Fiber's context and this one's in.
178  Fiber *prev = _currentFiber;
179  Fiber *next = this;
180  _currentFiber = next;
181  if (_setjmp(prev->jmp) == 0)
182  _longjmp(next->jmp, 1);
183 }
184 
185 Fiber *Fiber::currentFiber() { return _currentFiber; }
186 Fiber *Fiber::primaryFiber() { return &_primaryFiber; }
187 
188 } // namespace gem5
fatal
#define fatal(...)
This implements a cprintf based fatal() function.
Definition: logging.hh:189
gem5::Fiber::guardPage
void * guardPage
Definition: fiber.hh:158
gem5::Fiber::run
void run()
Start executing the fiber represented by this object.
Definition: fiber.cc:166
gem5::Fiber::ctx
ucontext_t ctx
Definition: fiber.hh:148
gem5::Fiber::guardPageSize
size_t guardPageSize
Definition: fiber.hh:159
gem5::Fiber::setStarted
void setStarted()
Definition: fiber.hh:142
gem5::Fiber::createContext
void createContext()
Definition: fiber.cc:123
gem5::Fiber::~Fiber
virtual ~Fiber()
Definition: fiber.cc:112
gem5::Fiber::currentFiber
static Fiber * currentFiber()
Get a pointer to the current running Fiber.
Definition: fiber.cc:185
gem5::Fiber::main
virtual void main()=0
This method is called when this fiber is first run.
gem5::Fiber::start
void start()
Definition: fiber.cc:142
gem5::Fiber::primaryFiber
static Fiber * primaryFiber()
Get a pointer to the primary Fiber.
Definition: fiber.cc:186
gem5::Fiber::jmp
jmp_buf jmp
Definition: fiber.hh:151
gem5::Fiber::_finished
bool _finished
Definition: fiber.hh:165
gem5::X86ISA::stack
Bitfield< 17, 16 > stack
Definition: misc.hh:593
gem5::Fiber::_started
bool _started
Definition: fiber.hh:164
gem5::Fiber
This class represents a fiber, which is a light weight sort of thread which is cooperatively schedule...
Definition: fiber.hh:71
gem5::Fiber::stackSize
size_t stackSize
Definition: fiber.hh:157
gem5::Fiber::entryTrampoline
static void entryTrampoline()
Definition: fiber.cc:80
gem5::main
int main()
Definition: cprintftime.cc:58
panic_if
#define panic_if(cond,...)
Conditional panic macro that checks the supplied condition and only panics if the condition is true a...
Definition: logging.hh:203
logging.hh
gem5::Fiber::Fiber
Fiber(size_t stack_size=DefaultStackSize)
Definition: fiber.cc:85
gem5::Fiber::stack
void * stack
Definition: fiber.hh:156
gem5
Reference material can be found at the JEDEC website: UFS standard http://www.jedec....
Definition: decoder.cc:40
fiber.hh
gem5::Fiber::link
Fiber * link
Definition: fiber.hh:153
panic
#define panic(...)
This implements a cprintf based panic() function.
Definition: logging.hh:177

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