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/coroutine_int.h"
  28
  29 #ifdef CONFIG_VALGRIND_H
  30 #include <valgrind/valgrind.h>
  31 #endif
  32
  33 #if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
  34 #ifdef CONFIG_ASAN_IFACE_FIBER
  35 #define CONFIG_ASAN 1
  36 #include <sanitizer/asan_interface.h>
  37 #endif
  38 #endif
  39
  40 typedef struct {
  41     Coroutine base;
  42     void *stack;
  43     size_t stack_size;
  44     sigjmp_buf env;
  45
  46 #ifdef CONFIG_VALGRIND_H
  47     unsigned int valgrind_stack_id;
  48 #endif
  49
  50 } CoroutineUContext;
  51
  52 /**
  53  * Per-thread coroutine bookkeeping
  54  */
  55 static __thread CoroutineUContext leader;
  56 static __thread Coroutine *current;
  57
  58 /*
  59  * va_args to makecontext() must be type 'int', so passing
  60  * the pointer we need may require several int args. This
  61  * union is a quick hack to let us do that
  62  */
  63 union cc_arg {
  64     void *p;
  65     int i[2];
  66 };
  67
  68 static void finish_switch_fiber(void *fake_stack_save)
  69 {
  70 #ifdef CONFIG_ASAN
  71     const void *bottom_old;
  72     size_t size_old;
  73
  74     __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
  75
  76     if (!leader.stack) {
  77         leader.stack = (void *)bottom_old;
  78         leader.stack_size = size_old;
  79     }
  80 #endif
  81 }
  82
  83 static void start_switch_fiber(void **fake_stack_save,
  84                                const void *bottom, size_t size)
  85 {
  86 #ifdef CONFIG_ASAN
  87     __sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
  88 #endif
  89 }
  90
  91 static void coroutine_trampoline(int i0, int i1)
  92 {
  93     union cc_arg arg;
  94     CoroutineUContext *self;
  95     Coroutine *co;
  96     void *fake_stack_save = NULL;
  97
  98     finish_switch_fiber(NULL);
  99
 100     arg.i[0] = i0;
 101     arg.i[1] = i1;
 102     self = arg.p;
 103     co = &self->base;
 104
 105     /* Initialize longjmp environment and switch back the caller */
 106     if (!sigsetjmp(self->env, 0)) {
 107         start_switch_fiber(&fake_stack_save,
 108                            leader.stack, leader.stack_size);
 109         siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
 110     }
 111
 112     finish_switch_fiber(fake_stack_save);
 113
 114     while (true) {
 115         co->entry(co->entry_arg);
 116         qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
 117     }
 118 }
 119
 120 Coroutine *qemu_coroutine_new(void)
 121 {
 122     CoroutineUContext *co;
 123     ucontext_t old_uc, uc;
 124     sigjmp_buf old_env;
 125     union cc_arg arg = {0};
 126     void *fake_stack_save = NULL;
 127
 128     /* The ucontext functions preserve signal masks which incurs a
 129      * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
 130      * preserve signal masks but only works on the current stack.
 131      * Since we need a way to create and switch to a new stack, use
 132      * the ucontext functions for that but sigsetjmp()/siglongjmp() for
 133      * everything else.
 134      */
 135
 136     if (getcontext(&uc) == -1) {
 137         abort();
 138     }
 139
 140     co = g_malloc0(sizeof(*co));
 141     co->stack_size = COROUTINE_STACK_SIZE;
 142     co->stack = qemu_alloc_stack(&co->stack_size);
 143     co->base.entry_arg = &old_env; /* stash away our jmp_buf */
 144
 145     uc.uc_link = &old_uc;
 146     uc.uc_stack.ss_sp = co->stack;
 147     uc.uc_stack.ss_size = co->stack_size;
 148     uc.uc_stack.ss_flags = 0;
 149
 150 #ifdef CONFIG_VALGRIND_H
 151     co->valgrind_stack_id =
 152         VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
 153 #endif
 154
 155     arg.p = co;
 156
 157     makecontext(&uc, (void (*)(void))coroutine_trampoline,
 158                 2, arg.i[0], arg.i[1]);
 159
 160     /* swapcontext() in, siglongjmp() back out */
 161     if (!sigsetjmp(old_env, 0)) {
 162         start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
 163         swapcontext(&old_uc, &uc);
 164     }
 165
 166     finish_switch_fiber(fake_stack_save);
 167
 168     return &co->base;
 169 }
 170
 171 #ifdef CONFIG_VALGRIND_H
 172 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 173 /* Work around an unused variable in the valgrind.h macro... */
 174 #pragma GCC diagnostic push
 175 #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
 176 #endif
 177 static inline void valgrind_stack_deregister(CoroutineUContext *co)
 178 {
 179     VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
 180 }
 181 #if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
 182 #pragma GCC diagnostic pop
 183 #endif
 184 #endif
 185
 186 void qemu_coroutine_delete(Coroutine *co_)
 187 {
 188     CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
 189
 190 #ifdef CONFIG_VALGRIND_H
 191     valgrind_stack_deregister(co);
 192 #endif
 193
 194     qemu_free_stack(co->stack, co->stack_size);
 195     g_free(co);
 196 }
 197
 198 /* This function is marked noinline to prevent GCC from inlining it
 199  * into coroutine_trampoline(). If we allow it to do that then it
 200  * hoists the code to get the address of the TLS variable "current"
 201  * out of the while() loop. This is an invalid transformation because
 202  * the sigsetjmp() call may be called when running thread A but
 203  * return in thread B, and so we might be in a different thread
 204  * context each time round the loop.
 205  */
 206 CoroutineAction __attribute__((noinline))
 207 qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
 208                       CoroutineAction action)
 209 {
 210     CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
 211     CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
 212     int ret;
 213     void *fake_stack_save = NULL;
 214
 215     current = to_;
 216
 217     ret = sigsetjmp(from->env, 0);
 218     if (ret == 0) {
 219         start_switch_fiber(action == COROUTINE_TERMINATE ?
 220                            NULL : &fake_stack_save, to->stack, to->stack_size);
 221         siglongjmp(to->env, action);
 222     }
 223
 224     finish_switch_fiber(fake_stack_save);
 225
 226     return ret;
 227 }
 228
 229 Coroutine *qemu_coroutine_self(void)
 230 {
 231     if (!current) {
 232         current = &leader.base;
 233     }
 234     return current;
 235 }
 236
 237 bool qemu_in_coroutine(void)
 238 {
 239     return current && current->caller;
 240 }