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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>
95 lines
2.8 KiB
C
95 lines
2.8 KiB
C
/* Initialization code run first thing by the ELF startup code. Common version
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Copyright (C) 1995-2020 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 <stdio.h>
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#include <stdlib.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <sysdep.h>
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#include <fpu_control.h>
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#include <sys/param.h>
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#include <sys/types.h>
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#include <libc-internal.h>
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#include <ldsodefs.h>
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/* Set nonzero if we have to be prepared for more than one libc being
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used in the process. Safe assumption if initializer never runs. */
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int __libc_multiple_libcs attribute_hidden = 1;
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/* Remember the command line argument and enviroment contents for
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later calls of initializers for dynamic libraries. */
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int __libc_argc attribute_hidden;
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char **__libc_argv attribute_hidden;
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void
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__libc_init_first (int argc, char **argv, char **envp)
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{
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#ifdef SHARED
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/* For DSOs we do not need __libc_init_first but an ELF constructor. */
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}
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static void __attribute__ ((constructor))
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_init_first (int argc, char **argv, char **envp)
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{
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#endif
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__libc_multiple_libcs = &_dl_starting_up && !_dl_starting_up;
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/* Make sure we don't initialize twice. */
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if (!__libc_multiple_libcs)
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{
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/* Set the FPU control word to the proper default value if the
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kernel would use a different value. */
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if (__fpu_control != GLRO(dl_fpu_control))
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__setfpucw (__fpu_control);
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}
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/* Save the command-line arguments. */
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__libc_argc = argc;
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__libc_argv = argv;
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__environ = envp;
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#ifndef SHARED
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/* First the initialization which normally would be done by the
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dynamic linker. */
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_dl_non_dynamic_init ();
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#endif
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__init_misc (argc, argv, envp);
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#if defined SHARED && !defined NO_CTORS_DTORS_SECTIONS
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__libc_global_ctors ();
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#endif
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}
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/* This function is defined here so that if this file ever gets into
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ld.so we will get a link error. Having this file silently included
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in ld.so causes disaster, because the _init_first definition above
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will cause ld.so to gain an ELF constructor, which is not a cool
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thing. */
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extern void _dl_start (void) __attribute__ ((noreturn));
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void
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_dl_start (void)
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{
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abort ();
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}
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