src/rseq.c

   1 // SPDX-License-Identifier: LGPL-2.1-only
   2 /*
   3  * rseq.c
   4  *
   5  * Copyright (C) 2016 Mathieu Desnoyers <mathieu.desnoyers@efficios.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; only
  10  * version 2.1 of the License.
  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 #ifndef _GNU_SOURCE
  18 #define _GNU_SOURCE
  19 #endif
  20 #include <errno.h>
  21 #include <sched.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <unistd.h>
  26 #include <syscall.h>
  27 #include <assert.h>
  28 #include <signal.h>
  29 #include <limits.h>
  30
  31 #include <rseq/rseq.h>
  32
  33 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
  34
  35 __thread volatile struct rseq __rseq_abi = {
  36         .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
  37 };
  38
  39 /*
  40  * Shared with other libraries. This library may take rseq ownership if it is
  41  * still 0 when executing the library constructor. Set to 1 by library
  42  * constructor when handling rseq. Set to 0 in destructor if handling rseq.
  43  */
  44 int __rseq_handled;
  45
  46 /* Whether this library have ownership of rseq registration. */
  47 static int rseq_ownership;
  48
  49 static __thread volatile uint32_t __rseq_refcount;
  50
  51 static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
  52                     int flags, uint32_t sig)
  53 {
  54         return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
  55 }
  56
  57 int rseq_available(void)
  58 {
  59         int rc;
  60
  61         rc = sys_rseq(NULL, 0, 0, 0);
  62         if (rc != -1)
  63                 abort();
  64         switch (errno) {
  65         case ENOSYS:
  66                 return 0;
  67         case EINVAL:
  68                 return 1;
  69         default:
  70                 abort();
  71         }
  72 }
  73
  74 static void signal_off_save(sigset_t *oldset)
  75 {
  76         sigset_t set;
  77         int ret;
  78
  79         sigfillset(&set);
  80         ret = pthread_sigmask(SIG_BLOCK, &set, oldset);
  81         if (ret)
  82                 abort();
  83 }
  84
  85 static void signal_restore(sigset_t oldset)
  86 {
  87         int ret;
  88
  89         ret = pthread_sigmask(SIG_SETMASK, &oldset, NULL);
  90         if (ret)
  91                 abort();
  92 }
  93
  94 int rseq_register_current_thread(void)
  95 {
  96         int rc, ret = 0;
  97         sigset_t oldset;
  98
  99         if (!rseq_ownership)
 100                 return 0;
 101         signal_off_save(&oldset);
 102         if (__rseq_refcount == UINT_MAX) {
 103                 ret = -1;
 104                 goto end;
 105         }
 106         if (__rseq_refcount++)
 107                 goto end;
 108         rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
 109         if (!rc) {
 110                 assert(rseq_current_cpu_raw() >= 0);
 111                 goto end;
 112         }
 113         if (errno != EBUSY)
 114                 __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
 115         ret = -1;
 116         __rseq_refcount--;
 117 end:
 118         signal_restore(oldset);
 119         return ret;
 120 }
 121
 122 int rseq_unregister_current_thread(void)
 123 {
 124         int rc, ret = 0;
 125         sigset_t oldset;
 126
 127         if (!rseq_ownership)
 128                 return 0;
 129         signal_off_save(&oldset);
 130         if (!__rseq_refcount) {
 131                 ret = -1;
 132                 goto end;
 133         }
 134         if (--__rseq_refcount)
 135                 goto end;
 136         rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
 137                       RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
 138         if (!rc)
 139                 goto end;
 140         __rseq_refcount = 1;
 141         ret = -1;
 142 end:
 143         signal_restore(oldset);
 144         return ret;
 145 }
 146
 147 int32_t rseq_fallback_current_cpu(void)
 148 {
 149         int32_t cpu;
 150
 151         cpu = sched_getcpu();
 152         if (cpu < 0) {
 153                 perror("sched_getcpu()");
 154                 abort();
 155         }
 156         return cpu;
 157 }
 158
 159 void __attribute__((constructor)) rseq_init(void)
 160 {
 161         /* Check whether rseq is handled by another library. */
 162         if (__rseq_handled)
 163                 return;
 164         __rseq_handled = 1;
 165         rseq_ownership = 1;
 166 }
 167
 168 void __attribute__((destructor)) rseq_fini(void)
 169 {
 170         if (!rseq_ownership)
 171                 return;
 172         __rseq_handled = 0;
 173         rseq_ownership = 0;
 174 }