mirror of
https://github.com/fluencelabs/musl
synced 2025-06-24 20:21:59 +00:00
e803829e6b
if a multithreaded program became non-multithreaded (i.e. all other threads exited) while one thread held an internal lock, the remaining thread would fail to release the lock. the the program then became multithreaded again at a later time, any further attempts to obtain the lock would deadlock permanently. the underlying cause is that the value of libc.threads_minus_1 at unlock time might not match the value at lock time. one solution would be returning a flag to the caller indicating whether the lock was taken and needs to be unlocked, but there is a simpler solution: using the lock itself as such a flag. note that this flag is not needed anyway for correctness; if the lock is not held, the unlock code is harmless. however, the memory synchronization properties associated with a_store are costly on some archs, so it's best to avoid executing the unlock code when it is unnecessary.
75 lines
1.5 KiB
C
75 lines
1.5 KiB
C
#ifndef LIBC_H
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#define LIBC_H
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#include <stdlib.h>
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#include <stdio.h>
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#include <limits.h>
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struct __libc {
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void *main_thread;
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int threaded;
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int secure;
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size_t *auxv;
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volatile int threads_minus_1;
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int canceldisable;
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FILE *ofl_head;
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int ofl_lock[2];
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size_t tls_size;
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size_t page_size;
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};
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extern size_t __hwcap;
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#ifndef PAGE_SIZE
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#define PAGE_SIZE libc.page_size
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#endif
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#if !defined(__PIC__) || (100*__GNUC__+__GNUC_MINOR__ >= 303 && !defined(__PCC__))
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#ifdef __PIC__
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#if __GNUC__ < 4
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#define BROKEN_VISIBILITY 1
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#endif
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#define ATTR_LIBC_VISIBILITY __attribute__((visibility("hidden")))
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#else
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#define ATTR_LIBC_VISIBILITY
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#endif
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extern struct __libc __libc ATTR_LIBC_VISIBILITY;
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#define libc __libc
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#else
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#define USE_LIBC_ACCESSOR
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#define ATTR_LIBC_VISIBILITY
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extern struct __libc *__libc_loc(void) __attribute__((const));
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#define libc (*__libc_loc())
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#endif
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/* Designed to avoid any overhead in non-threaded processes */
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void __lock(volatile int *) ATTR_LIBC_VISIBILITY;
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void __unlock(volatile int *) ATTR_LIBC_VISIBILITY;
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int __lockfile(FILE *) ATTR_LIBC_VISIBILITY;
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void __unlockfile(FILE *) ATTR_LIBC_VISIBILITY;
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#define LOCK(x) __lock(x)
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#define UNLOCK(x) __unlock(x)
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void __synccall(void (*)(void *), void *);
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int __setxid(int, int, int, int);
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extern char **__environ;
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#undef weak_alias
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#define weak_alias(old, new) \
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extern __typeof(old) new __attribute__((weak, alias(#old)))
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#undef LFS64_2
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#define LFS64_2(x, y) weak_alias(x, y)
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#undef LFS64
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#define LFS64(x) LFS64_2(x, x##64)
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#endif
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