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ec935dea63
This function is defined in libc.so, and the dynamic loader calls right after relocation has been finished, before any ELF constructors or the preinit function is invoked. It is also used in the static build for initializing parts of the static libc. To locate __libc_early_init, a direct symbol lookup function is used, _dl_lookup_direct. It does not search the entire symbol scope and consults merely a single link map. This function could also be used to implement lookups in the vDSO (as an optimization). A per-namespace variable (libc_map) is added for locating libc.so, to avoid repeated traversals of the search scope. It is similar to GL(dl_initfirst). An alternative would have been to thread a context argument from _dl_open down to _dl_map_object_from_fd (where libc.so is identified). This could have avoided the global variable, but the change would be larger as a result. It would not have been possible to use this to replace GL(dl_initfirst) because that global variable is used to pass the function pointer past the stack switch from dl_main to the main program. Replacing that requires adding a new argument to _dl_init, which in turn needs changes to the architecture-specific libc.so startup code written in assembler. __libc_early_init should not be used to replace _dl_var_init (as it exists today on some architectures). Instead, _dl_lookup_direct should be used to look up a new variable symbol in libc.so, and that should then be initialized from the dynamic loader, immediately after the object has been loaded in _dl_map_object_from_fd (before relocation is run). This way, more IFUNC resolvers which depend on these variables will work. Reviewed-by: Carlos O'Donell <carlos@redhat.com>
349 lines
10 KiB
C
349 lines
10 KiB
C
/* Copyright (C) 1998-2020 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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<https://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <unistd.h>
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#include <ldsodefs.h>
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#include <exit-thread.h>
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#include <libc-internal.h>
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#include <elf/libc-early-init.h>
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#include <elf/dl-tunables.h>
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extern void __libc_init_first (int argc, char **argv, char **envp);
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#include <tls.h>
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#ifndef SHARED
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# include <dl-osinfo.h>
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# ifndef THREAD_SET_STACK_GUARD
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/* Only exported for architectures that don't store the stack guard canary
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in thread local area. */
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uintptr_t __stack_chk_guard attribute_relro;
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# endif
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# ifndef THREAD_SET_POINTER_GUARD
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/* Only exported for architectures that don't store the pointer guard
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value in thread local area. */
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uintptr_t __pointer_chk_guard_local
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attribute_relro attribute_hidden __attribute__ ((nocommon));
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# endif
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#endif
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#ifdef HAVE_PTR_NTHREADS
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/* We need atomic operations. */
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# include <atomic.h>
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#endif
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#ifndef SHARED
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# include <link.h>
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# include <dl-irel.h>
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# ifdef ELF_MACHINE_IRELA
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# define IREL_T ElfW(Rela)
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# define IPLT_START __rela_iplt_start
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# define IPLT_END __rela_iplt_end
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# define IREL elf_irela
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# elif defined ELF_MACHINE_IREL
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# define IREL_T ElfW(Rel)
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# define IPLT_START __rel_iplt_start
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# define IPLT_END __rel_iplt_end
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# define IREL elf_irel
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# endif
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static void
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apply_irel (void)
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{
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# ifdef IREL
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/* We use weak references for these so that we'll still work with a linker
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that doesn't define them. Such a linker doesn't support IFUNC at all
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and so uses won't work, but a statically-linked program that doesn't
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use any IFUNC symbols won't have a problem. */
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extern const IREL_T IPLT_START[] __attribute__ ((weak));
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extern const IREL_T IPLT_END[] __attribute__ ((weak));
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for (const IREL_T *ipltent = IPLT_START; ipltent < IPLT_END; ++ipltent)
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IREL (ipltent);
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# endif
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}
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#endif
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#ifdef LIBC_START_MAIN
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# ifdef LIBC_START_DISABLE_INLINE
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# define STATIC static
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# else
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# define STATIC static inline __attribute__ ((always_inline))
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# endif
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#else
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# define STATIC
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# define LIBC_START_MAIN __libc_start_main
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#endif
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#ifdef MAIN_AUXVEC_ARG
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/* main gets passed a pointer to the auxiliary. */
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# define MAIN_AUXVEC_DECL , void *
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# define MAIN_AUXVEC_PARAM , auxvec
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#else
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# define MAIN_AUXVEC_DECL
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# define MAIN_AUXVEC_PARAM
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#endif
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#ifndef ARCH_INIT_CPU_FEATURES
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# define ARCH_INIT_CPU_FEATURES()
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#endif
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#include <libc-start.h>
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STATIC int LIBC_START_MAIN (int (*main) (int, char **, char **
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MAIN_AUXVEC_DECL),
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int argc,
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char **argv,
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#ifdef LIBC_START_MAIN_AUXVEC_ARG
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ElfW(auxv_t) *auxvec,
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#endif
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__typeof (main) init,
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void (*fini) (void),
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void (*rtld_fini) (void),
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void *stack_end)
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__attribute__ ((noreturn));
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/* Note: the fini parameter is ignored here for shared library. It
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is registered with __cxa_atexit. This had the disadvantage that
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finalizers were called in more than one place. */
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STATIC int
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LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
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int argc, char **argv,
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#ifdef LIBC_START_MAIN_AUXVEC_ARG
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ElfW(auxv_t) *auxvec,
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#endif
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__typeof (main) init,
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void (*fini) (void),
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void (*rtld_fini) (void), void *stack_end)
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{
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/* Result of the 'main' function. */
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int result;
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__libc_multiple_libcs = &_dl_starting_up && !_dl_starting_up;
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#ifndef SHARED
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_dl_relocate_static_pie ();
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char **ev = &argv[argc + 1];
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__environ = ev;
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/* Store the lowest stack address. This is done in ld.so if this is
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the code for the DSO. */
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__libc_stack_end = stack_end;
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# ifdef HAVE_AUX_VECTOR
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/* First process the auxiliary vector since we need to find the
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program header to locate an eventually present PT_TLS entry. */
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# ifndef LIBC_START_MAIN_AUXVEC_ARG
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ElfW(auxv_t) *auxvec;
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{
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char **evp = ev;
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while (*evp++ != NULL)
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;
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auxvec = (ElfW(auxv_t) *) evp;
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}
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# endif
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_dl_aux_init (auxvec);
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if (GL(dl_phdr) == NULL)
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# endif
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{
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/* Starting from binutils-2.23, the linker will define the
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magic symbol __ehdr_start to point to our own ELF header
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if it is visible in a segment that also includes the phdrs.
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So we can set up _dl_phdr and _dl_phnum even without any
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information from auxv. */
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extern const ElfW(Ehdr) __ehdr_start
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__attribute__ ((weak, visibility ("hidden")));
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if (&__ehdr_start != NULL)
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{
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assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
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GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
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GL(dl_phnum) = __ehdr_start.e_phnum;
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}
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}
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/* Initialize very early so that tunables can use it. */
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__libc_init_secure ();
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__tunables_init (__environ);
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ARCH_INIT_CPU_FEATURES ();
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/* Perform IREL{,A} relocations. */
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ARCH_SETUP_IREL ();
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/* The stack guard goes into the TCB, so initialize it early. */
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ARCH_SETUP_TLS ();
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/* In some architectures, IREL{,A} relocations happen after TLS setup in
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order to let IFUNC resolvers benefit from TCB information, e.g. powerpc's
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hwcap and platform fields available in the TCB. */
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ARCH_APPLY_IREL ();
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/* Set up the stack checker's canary. */
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uintptr_t stack_chk_guard = _dl_setup_stack_chk_guard (_dl_random);
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# ifdef THREAD_SET_STACK_GUARD
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THREAD_SET_STACK_GUARD (stack_chk_guard);
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# else
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__stack_chk_guard = stack_chk_guard;
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# endif
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# ifdef DL_SYSDEP_OSCHECK
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if (!__libc_multiple_libcs)
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{
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/* This needs to run to initiliaze _dl_osversion before TLS
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setup might check it. */
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DL_SYSDEP_OSCHECK (__libc_fatal);
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}
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# endif
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/* Initialize libpthread if linked in. */
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if (__pthread_initialize_minimal != NULL)
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__pthread_initialize_minimal ();
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/* Set up the pointer guard value. */
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uintptr_t pointer_chk_guard = _dl_setup_pointer_guard (_dl_random,
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stack_chk_guard);
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# ifdef THREAD_SET_POINTER_GUARD
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THREAD_SET_POINTER_GUARD (pointer_chk_guard);
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# else
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__pointer_chk_guard_local = pointer_chk_guard;
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# endif
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#endif /* !SHARED */
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/* Register the destructor of the dynamic linker if there is any. */
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if (__glibc_likely (rtld_fini != NULL))
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__cxa_atexit ((void (*) (void *)) rtld_fini, NULL, NULL);
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#ifndef SHARED
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/* Perform early initialization. In the shared case, this function
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is called from the dynamic loader as early as possible. */
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__libc_early_init ();
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/* Call the initializer of the libc. This is only needed here if we
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are compiling for the static library in which case we haven't
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run the constructors in `_dl_start_user'. */
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__libc_init_first (argc, argv, __environ);
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/* Register the destructor of the program, if any. */
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if (fini)
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__cxa_atexit ((void (*) (void *)) fini, NULL, NULL);
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/* Some security at this point. Prevent starting a SUID binary where
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the standard file descriptors are not opened. We have to do this
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only for statically linked applications since otherwise the dynamic
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loader did the work already. */
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if (__builtin_expect (__libc_enable_secure, 0))
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__libc_check_standard_fds ();
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#endif
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/* Call the initializer of the program, if any. */
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#ifdef SHARED
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if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS, 0))
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GLRO(dl_debug_printf) ("\ninitialize program: %s\n\n", argv[0]);
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#endif
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if (init)
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(*init) (argc, argv, __environ MAIN_AUXVEC_PARAM);
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#ifdef SHARED
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/* Auditing checkpoint: we have a new object. */
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if (__glibc_unlikely (GLRO(dl_naudit) > 0))
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{
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struct audit_ifaces *afct = GLRO(dl_audit);
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struct link_map *head = GL(dl_ns)[LM_ID_BASE]._ns_loaded;
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for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
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{
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if (afct->preinit != NULL)
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afct->preinit (&link_map_audit_state (head, cnt)->cookie);
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afct = afct->next;
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}
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}
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#endif
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#ifdef SHARED
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if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_IMPCALLS))
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GLRO(dl_debug_printf) ("\ntransferring control: %s\n\n", argv[0]);
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#endif
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#ifndef SHARED
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_dl_debug_initialize (0, LM_ID_BASE);
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#endif
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#ifdef HAVE_CLEANUP_JMP_BUF
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/* Memory for the cancellation buffer. */
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struct pthread_unwind_buf unwind_buf;
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int not_first_call;
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not_first_call = setjmp ((struct __jmp_buf_tag *) unwind_buf.cancel_jmp_buf);
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if (__glibc_likely (! not_first_call))
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{
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struct pthread *self = THREAD_SELF;
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/* Store old info. */
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unwind_buf.priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
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unwind_buf.priv.data.cleanup = THREAD_GETMEM (self, cleanup);
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/* Store the new cleanup handler info. */
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THREAD_SETMEM (self, cleanup_jmp_buf, &unwind_buf);
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/* Run the program. */
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result = main (argc, argv, __environ MAIN_AUXVEC_PARAM);
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}
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else
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{
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/* Remove the thread-local data. */
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# ifdef SHARED
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PTHFCT_CALL (ptr__nptl_deallocate_tsd, ());
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# else
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extern void __nptl_deallocate_tsd (void) __attribute ((weak));
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__nptl_deallocate_tsd ();
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# endif
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/* One less thread. Decrement the counter. If it is zero we
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terminate the entire process. */
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result = 0;
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# ifdef SHARED
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unsigned int *ptr = __libc_pthread_functions.ptr_nthreads;
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# ifdef PTR_DEMANGLE
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PTR_DEMANGLE (ptr);
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# endif
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# else
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extern unsigned int __nptl_nthreads __attribute ((weak));
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unsigned int *const ptr = &__nptl_nthreads;
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# endif
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if (! atomic_decrement_and_test (ptr))
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/* Not much left to do but to exit the thread, not the process. */
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__exit_thread ();
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}
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#else
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/* Nothing fancy, just call the function. */
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result = main (argc, argv, __environ MAIN_AUXVEC_PARAM);
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#endif
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exit (result);
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}
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