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It can be used to speed up the libgcc unwinder, and the internal _dl_find_dso_for_object function (which is used for caller identification in dlopen and related functions, and in dladdr). _dl_find_object is in the internal namespace due to bug 28503. If libgcc switches to _dl_find_object, this namespace issue will be fixed. It is located in libc for two reasons: it is necessary to forward the call to the static libc after static dlopen, and there is a link ordering issue with -static-libgcc and libgcc_eh.a because libc.so is not a linker script that includes ld.so in the glibc build tree (so that GCC's internal -lc after libgcc_eh.a does not pick up ld.so). It is necessary to do the i386 customization in the sysdeps/x86/bits/dl_find_object.h header shared with x86-64 because otherwise, multilib installations are broken. The implementation uses software transactional memory, as suggested by Torvald Riegel. Two copies of the supporting data structures are used, also achieving full async-signal-safety. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
116 lines
4.0 KiB
C
116 lines
4.0 KiB
C
/* Locating objects in the process image. ld.so implementation.
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Copyright (C) 2021 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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#ifndef _DL_FIND_EH_FRAME_H
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#define _DL_FIND_EH_FRAME_H
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#include <assert.h>
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#include <dlfcn.h>
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#include <ldsodefs.h>
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#include <stdbool.h>
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#include <stdint.h>
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/* Internal version of struct dl_find_object. Does not include the
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(yet unused) flags member. We need to make a copy of data also in
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struct link_map to support non-contiguous mappings, and to support
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software transactional memory (the link map is not covered by
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transactions). */
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struct dl_find_object_internal
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{
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uintptr_t map_start;
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uintptr_t map_end; /* Set to map_start by dlclose. */
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struct link_map *map; /* Set to NULL by dlclose. */
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void *eh_frame;
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#if DLFO_STRUCT_HAS_EH_DBASE
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void *eh_dbase;
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#endif
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#if DLFO_STRUCT_HAS_EH_COUNT
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int eh_count;
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#endif
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};
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static inline void
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_dl_find_object_to_external (struct dl_find_object_internal *internal,
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struct dl_find_object *external)
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{
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external->dlfo_flags = 0;
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external->dlfo_map_start = (void *) internal->map_start;
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external->dlfo_map_end = (void *) internal->map_end;
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external->dlfo_link_map = internal->map;
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external->dlfo_eh_frame = internal->eh_frame;
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# if DLFO_STRUCT_HAS_EH_DBASE
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external->dlfo_eh_dbase = internal->eh_dbase;
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# endif
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# if DLFO_STRUCT_HAS_EH_COUNT
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external->dlfo_eh_count = internal->eh_count;
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# endif
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}
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/* Extract the object location data from a link map and writes it to
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*RESULT. */
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static void __attribute__ ((unused))
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_dl_find_object_from_map (struct link_map *l,
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struct dl_find_object_internal *result)
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{
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result->map_start = (uintptr_t) l->l_map_start;
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result->map_end = (uintptr_t) l->l_map_end;
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result->map = l;
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#if DLFO_STRUCT_HAS_EH_DBASE
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result->eh_dbase = (void *) l->l_info[DT_PLTGOT];
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#endif
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for (const ElfW(Phdr) *ph = l->l_phdr, *ph_end = l->l_phdr + l->l_phnum;
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ph < ph_end; ++ph)
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if (ph->p_type == DLFO_EH_SEGMENT_TYPE)
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{
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result->eh_frame = (void *) (ph->p_vaddr + l->l_addr);
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#if DLFO_STRUCT_HAS_EH_COUNT
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result->eh_count = ph->p_memsz / 8;
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#endif
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return;
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}
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/* Object has no exception handling segment. */
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result->eh_frame = NULL;
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#if DLFO_STRUCT_HAS_EH_COUNT
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result->eh_count = 0;
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#endif
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}
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/* Called by the dynamic linker to set up the data structures for the
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initially loaded objects. This creates a few persistent
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allocations, so it should be called with the minimal malloc. */
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void _dl_find_object_init (void) attribute_hidden;
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/* Called by dlopen/dlmopen to add new objects to the DWARF EH frame
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data structures. NEW_MAP is the dlopen'ed link map. Link maps on
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the l_next list are added if l_object_processed is 0. Needs to
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be protected by loader write lock. Returns true on success, false
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on malloc failure. */
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bool _dl_find_object_update (struct link_map *new_map) attribute_hidden;
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/* Called by dlclose to remove the link map from the DWARF EH frame
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data structures. Needs to be protected by loader write lock. */
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void _dl_find_object_dlclose (struct link_map *l) attribute_hidden;
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/* Called from __libc_freeres to deallocate malloc'ed memory. */
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void _dl_find_object_freeres (void) attribute_hidden;
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#endif /* _DL_FIND_OBJECT_H */
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