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elf: Add _dl_find_object function

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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>
This commit is contained in:
Florian Weimer
2021-12-28 22:52:56 +01:00
parent 83b8d5027d
commit 5d28a8962d
73 changed files with 2038 additions and 18 deletions
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4
elf/dl-close.c
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@@ -32,6 +32,7 @@
#include <sysdep-cancel.h>
#include <tls.h>
#include <stap-probe.h>
#include <dl-find_object.h>
#include <dl-unmap-segments.h>
@@ -682,6 +683,9 @@ _dl_close_worker (struct link_map *map, bool force)
if (imap->l_next != NULL)
imap->l_next->l_prev = imap->l_prev;
/* Update the data used by _dl_find_object. */
_dl_find_object_dlclose (imap);
free (imap->l_versions);
if (imap->l_origin != (char *) -1)
free ((char *) imap->l_origin);