util/coroutine-ucontext.c

   1 /*
   2  * ucontext coroutine initialization code
   3  *
   4  * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>
   5  * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>
   6  *
   7  * This library is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.0 of the License, or (at your option) any later version.
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  19  */
  20
  21 /* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
  22 #ifdef _FORTIFY_SOURCE
  23 #undef _FORTIFY_SOURCE
  24 #endif
  25 #include "qemu/osdep.h"
  26 #include <ucontext.h>
  27 #include "qemu-common.h"
  28 #include "qemu/coroutine_int.h"
  29
  30 #ifdef CONFIG_VALGRIND_H
  31 #include <valgrind/valgrind.h>
  32 #endif
  33
  34 #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
  35 #ifdef CONFIG_ASAN_IFACE_FIBER
  36 #define CONFIG_ASAN 1
  37 #include <sanitizer/asan_interface.h>
  38 #endif
  39 #endif
  40
  41 typedef struct {
  42     Coroutine base;
  43     void *stack;
  44     size_t stack_size;
  45     sigjmp_buf env;
  46
  47 #ifdef CONFIG_VALGRIND_H
  48     unsigned int valgrind_stack_id;
  49 #endif
  50
  51 } CoroutineUContext;
  52
  53 /**
  54  * Per-thread coroutine bookkeeping
  55  */
  56 static __thread CoroutineUContext leader;
  57 static __thread Coroutine *current;
  58
  59 /*
  60  * va_args to makecontext() must be type 'int', so passing
  61  * the pointer we need may require several int args. This
  62  * union is a quick hack to let us do that
  63  */
  64 union cc_arg {
  65     void *p;
  66     int i[2];
  67 };
  68
  69 static void finish_switch_fiber(void *fake_stack_save)
  70 {
  71 #ifdef CONFIG_ASAN
  72     const void *bottom_old;
  73     size_t size_old;
  74
  75     __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
  76
  77     if (!leader.stack) {
  78         leader.stack = (void *)bottom_old;
  79         leader.stack_size = size_old;
  80     }
  81 #endif
  82 }
  83
  84 static void start_switch_fiber(void **fake_stack_save,
  85                                const void *bottom, size_t size)
  86 {
  87 #ifdef CONFIG_ASAN
  88     __sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
  89 #endif
  90 }
  91
  92 static void coroutine_trampoline(int i0, int i1)
  93 {
  94     union cc_arg arg;
  95     CoroutineUContext *self;
  96     Coroutine *co;
  97     void *fake_stack_save = NULL;
  98
  99     finish_switch_fiber(NULL);
 100
 101     arg.i[0] = i0;
 102     arg.i[1] = i1;
 103     self = arg.p;
 104     co = &self->base;
 105
 106     /* Initialize longjmp environment and switch back the caller */
 107     if (!sigsetjmp(self->env, 0)) {
 108         start_switch_fiber(&fake_stack_save,
 109                            leader.stack, leader.stack_size);
 110         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
 111     }
 112
 113     finish_switch_fiber(fake_stack_save);
 114
 115     while (true) {
 116         co->entry(co->entry_arg);
 117         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 118     }
 119 }
 120
 121 Coroutine *qemu_coroutine_new(void)
 122 {
 123     CoroutineUContext *co;
 124     ucontext_t old_uc, uc;
 125     sigjmp_buf old_env;
 126     union cc_arg arg = {0};
 127     void *fake_stack_save = NULL;
 128
 129     /* The ucontext functions preserve signal masks which incurs a
 130      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
 131      * preserve signal masks but only works on the current stack.
 132      * Since we need a way to create and switch to a new stack, use
 133      * the ucontext functions for that but sigsetjmp()/siglongjmp() for
 134      * everything else.
 135      */
 136
 137     if (getcontext(&uc) == -1) {
 138         abort();
 139     }
 140
 141     co = g_malloc0(sizeof(*co));
 142     co->stack_size = COROUTINE_STACK_SIZE;
 143     co->stack = qemu_alloc_stack(&co->stack_size);
 144     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 145
 146     uc.uc_link = &old_uc;
 147     uc.uc_stack.ss_sp = co->stack;
 148     uc.uc_stack.ss_size = co->stack_size;
 149     uc.uc_stack.ss_flags = 0;
 150
 151 #ifdef CONFIG_VALGRIND_H
 152     co->valgrind_stack_id =
 153         VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
 154 #endif
 155
 156     arg.p = co;
 157
 158     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 159                 2, arg.i[0], arg.i[1]);
 160
 161     /* swapcontext() in, siglongjmp() back out */
 162     if (!sigsetjmp(old_env, 0)) {
 163         start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
 164         swapcontext(&old_uc, &uc);
 165     }
 166
 167     finish_switch_fiber(fake_stack_save);
 168
 169     return &co->base;
 170 }
 171
 172 #ifdef CONFIG_VALGRIND_H
 173 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 174 /* Work around an unused variable in the valgrind.h macro... */
 175 #pragma GCC diagnostic push
 176 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 177 #endif
 178 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 179 {
 180     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 181 }
 182 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 183 #pragma GCC diagnostic pop
 184 #endif
 185 #endif
 186
 187 void qemu_coroutine_delete(Coroutine *co_)
 188 {
 189     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 190
 191 #ifdef CONFIG_VALGRIND_H
 192     valgrind_stack_deregister(co);
 193 #endif
 194
 195     qemu_free_stack(co->stack, co->stack_size);
 196     g_free(co);
 197 }
 198
 199 /* This function is marked noinline to prevent GCC from inlining it
 200  * into coroutine_trampoline(). If we allow it to do that then it
 201  * hoists the code to get the address of the TLS variable "current"
 202  * out of the while() loop. This is an invalid transformation because
 203  * the sigsetjmp() call may be called when running thread A but
 204  * return in thread B, and so we might be in a different thread
 205  * context each time round the loop.
 206  */
 207 CoroutineAction __attribute__((noinline))
 208 qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 209                       CoroutineAction action)
 210 {
 211     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 212     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 213     int ret;
 214     void *fake_stack_save = NULL;
 215
 216     current = to_;
 217
 218     ret = sigsetjmp(from->env, 0);
 219     if (ret == 0) {
 220         start_switch_fiber(action == COROUTINE_TERMINATE ?
 221                            NULL : &fake_stack_save, to->stack, to->stack_size);
 222         siglongjmp(to->env, action);
 223     }
 224
 225     finish_switch_fiber(fake_stack_save);
 226
 227     return ret;
 228 }
 229
 230 Coroutine *qemu_coroutine_self(void)
 231 {
 232     if (!current) {
 233         current = &leader.base;
 234     }
 235     return current;
 236 }
 237
 238 bool qemu_in_coroutine(void)
 239 {
 240     return current && current->caller;
 241 }