69 lines
2.9 KiB
C
69 lines
2.9 KiB
C
/* Initialize pid and tid fields of struct pthread. NaCl version.
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Copyright (C) 2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <pthreadP.h>
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/* NaCl has no concept of PID or TID, nor even any notion of an
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identifier for a thread within the process. But various places in
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the NPTL implementation rely on using the 'tid' field of the TCB
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(struct pthread) as an identifier that is unique at least among all
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live threads in the process. So we must synthesize some number to
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use. Conveniently, the 'pthread_t' value itself is already unique
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in exactly this way (because it's the 'struct pthread' pointer).
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The only wrinkle is that 'tid' is a (32-bit) 'int' and its high
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(sign) bit is used for special purposes, so we must be absolutely
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sure that we never use a pointer value with the high bit set. (It
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also cannot be zero, but zero is never a valid pointer anyway.)
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The NaCl sandbox models for 32-bit machines limit the address space
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to less than 3GB (in fact, to 1GB), so it's already impossible that
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a valid pointer will have its high bit set. But the NaCl x86-64
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sandbox model allows a full 4GB of address space, so we cannot
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assume that an arbitrary pointer value will not have the high bit
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set. Conveniently, there are always unused bits in the pointer
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value for a 'struct pthread', because it is always aligned to at
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least 32 bits and so the low bits are always zero. Hence, we can
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safely avoid the danger of a nonzero high bit just by shifting the
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pointer value right. */
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static inline int
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__nacl_get_tid (struct pthread *pd)
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{
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uintptr_t id = (uintptr_t) pd;
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int tid = id >> 1;
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assert ((id & 1) == 0);
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assert (sizeof id == sizeof tid);
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assert (tid > 0);
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/* This ensures that NACL_EXITING_TID (lowlevellock.h) can never
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be a valid TID value. */
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assert ((tid & 1) == 0);
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return tid;
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}
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/* Initialize PD->pid and PD->tid for the initial thread. If there is
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setup required to arrange that __exit_thread causes PD->tid to be
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cleared and futex-woken, then this function should do that as well. */
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static inline void
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__pthread_initialize_pids (struct pthread *pd)
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{
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pd->tid = __nacl_get_tid (pd);
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pd->pid = -1;
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}
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