summaryrefslogtreecommitdiffstats
path: root/util/coroutine-ucontext.c
blob: 090ba21a13ea03459b3e79aa82ec0262591a49ea (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
/*
 * ucontext coroutine initialization code
 *
 * Copyright (C) 2006  Anthony Liguori <anthony@codemonkey.ws>
 * Copyright (C) 2011  Kevin Wolf <kwolf@redhat.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.0 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
#ifdef _FORTIFY_SOURCE
#undef _FORTIFY_SOURCE
#endif
#include "qemu/osdep.h"
#include <ucontext.h>
#include "qemu-common.h"
#include "qemu/coroutine_int.h"

#ifdef CONFIG_VALGRIND_H
#include <valgrind/valgrind.h>
#endif

#if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
#ifdef CONFIG_ASAN_IFACE_FIBER
#define CONFIG_ASAN 1
#include <sanitizer/asan_interface.h>
#endif
#endif

typedef struct {
    Coroutine base;
    void *stack;
    size_t stack_size;
    sigjmp_buf env;

#ifdef CONFIG_VALGRIND_H
    unsigned int valgrind_stack_id;
#endif

} CoroutineUContext;

/**
 * Per-thread coroutine bookkeeping
 */
static __thread CoroutineUContext leader;
static __thread Coroutine *current;

/*
 * va_args to makecontext() must be type 'int', so passing
 * the pointer we need may require several int args. This
 * union is a quick hack to let us do that
 */
union cc_arg {
    void *p;
    int i[2];
};

static void finish_switch_fiber(void *fake_stack_save)
{
#ifdef CONFIG_ASAN
    const void *bottom_old;
    size_t size_old;

    __sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);

    if (!leader.stack) {
        leader.stack = (void *)bottom_old;
        leader.stack_size = size_old;
    }
#endif
}

static void start_switch_fiber(void **fake_stack_save,
                               const void *bottom, size_t size)
{
#ifdef CONFIG_ASAN
    __sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
#endif
}

static void coroutine_trampoline(int i0, int i1)
{
    union cc_arg arg;
    CoroutineUContext *self;
    Coroutine *co;
    void *fake_stack_save = NULL;

    finish_switch_fiber(NULL);

    arg.i[0] = i0;
    arg.i[1] = i1;
    self = arg.p;
    co = &self->base;

    /* Initialize longjmp environment and switch back the caller */
    if (!sigsetjmp(self->env, 0)) {
        start_switch_fiber(&fake_stack_save,
                           leader.stack, leader.stack_size);
        siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
    }

    finish_switch_fiber(fake_stack_save);

    while (true) {
        co->entry(co->entry_arg);
        qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
    }
}

Coroutine *qemu_coroutine_new(void)
{
    CoroutineUContext *co;
    ucontext_t old_uc, uc;
    sigjmp_buf old_env;
    union cc_arg arg = {0};
    void *fake_stack_save = NULL;

    /* The ucontext functions preserve signal masks which incurs a
     * system call overhead.  sigsetjmp(buf, 0)/siglongjmp() does not
     * preserve signal masks but only works on the current stack.
     * Since we need a way to create and switch to a new stack, use
     * the ucontext functions for that but sigsetjmp()/siglongjmp() for
     * everything else.
     */

    if (getcontext(&uc) == -1) {
        abort();
    }

    co = g_malloc0(sizeof(*co));
    co->stack_size = COROUTINE_STACK_SIZE;
    co->stack = qemu_alloc_stack(&co->stack_size);
    co->base.entry_arg = &old_env; /* stash away our jmp_buf */

    uc.uc_link = &old_uc;
    uc.uc_stack.ss_sp = co->stack;
    uc.uc_stack.ss_size = co->stack_size;
    uc.uc_stack.ss_flags = 0;

#ifdef CONFIG_VALGRIND_H
    co->valgrind_stack_id =
        VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
#endif

    arg.p = co;

    makecontext(&uc, (void (*)(void))coroutine_trampoline,
                2, arg.i[0], arg.i[1]);

    /* swapcontext() in, siglongjmp() back out */
    if (!sigsetjmp(old_env, 0)) {
        start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
        swapcontext(&old_uc, &uc);
    }

    finish_switch_fiber(fake_stack_save);

    return &co->base;
}

#ifdef CONFIG_VALGRIND_H
#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
/* Work around an unused variable in the valgrind.h macro... */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
#endif
static inline void valgrind_stack_deregister(CoroutineUContext *co)
{
    VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
}
#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
#endif

void qemu_coroutine_delete(Coroutine *co_)
{
    CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);

#ifdef CONFIG_VALGRIND_H
    valgrind_stack_deregister(co);
#endif

    qemu_free_stack(co->stack, co->stack_size);
    g_free(co);
}

/* This function is marked noinline to prevent GCC from inlining it
 * into coroutine_trampoline(). If we allow it to do that then it
 * hoists the code to get the address of the TLS variable "current"
 * out of the while() loop. This is an invalid transformation because
 * the sigsetjmp() call may be called when running thread A but
 * return in thread B, and so we might be in a different thread
 * context each time round the loop.
 */
CoroutineAction __attribute__((noinline))
qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
                      CoroutineAction action)
{
    CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
    CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
    int ret;
    void *fake_stack_save = NULL;

    current = to_;

    ret = sigsetjmp(from->env, 0);
    if (ret == 0) {
        start_switch_fiber(action == COROUTINE_TERMINATE ?
                           NULL : &fake_stack_save, to->stack, to->stack_size);
        siglongjmp(to->env, action);
    }

    finish_switch_fiber(fake_stack_save);

    return ret;
}

Coroutine *qemu_coroutine_self(void)
{
    if (!current) {
        current = &leader.base;
    }
    return current;
}

bool qemu_in_coroutine(void)
{
    return current && current->caller;
}