We have this condition in `check_match' (in elf/dl-lookup.c):
if (__glibc_unlikely ((sym->st_value == 0 /* No value. */
&& stt != STT_TLS)
|| ELF_MACHINE_SYM_NO_MATCH (sym)
|| (type_class & (sym->st_shndx == SHN_UNDEF))))
return NULL;
which causes all !STT_TLS symbols whose value is zero to be silently
ignored in lookup. This may make sense for regular symbols, however not
for absolute (SHN_ABS) ones, where zero is like any value, there's no
special meaning attached to it.
Consequently legitimate programs fail, for example taking the
`elf/tst-absolute-sym' test case, substituting 0 for 0x55aa in
`elf/tst-absolute-sym-lib.lds' and then trying to run the resulting
program we get this:
$ .../elf/tst-absolute-sym
.../elf/tst-absolute-sym: symbol lookup error: .../elf/tst-absolute-sym-lib.so: undefined symbol: absolute
$
even though the symbol clearly is there:
$ readelf --dyn-syms .../elf/tst-absolute-sym-lib.so | grep '\babsolute\b'
7: 00000000 0 NOTYPE GLOBAL DEFAULT ABS absolute
$
The check for the zero value has been there since forever or commit
d66e34cd4234/08162fa88891 ("Implemented runtime dynamic linker to
support ELF shared libraries.") dating back to May 2nd 1995, and the
problem triggers regardless of commit e7feec374c ("elf: Correct
absolute (SHN_ABS) symbol run-time calculation [BZ #19818]") being
present or not.
Fix the issue then, by permitting `sym->st_value' to be 0 for SHN_ABS
symbols in lookup.
[BZ #23307]
* elf/dl-lookup.c (check_match): Do not reject a symbol whose
`st_value' is 0 if `st_shndx' is SHN_ABS.
* elf/tst-absolute-zero.c: New file.
* elf/tst-absolute-zero-lib.c: New file.
* elf/tst-absolute-zero-lib.lds: New file.
* elf/Makefile (tests): Add `tst-absolute-zero'.
(modules-names): Add `tst-absolute-zero-lib'.
(LDLIBS-tst-absolute-zero-lib.so): New variable.
($(objpfx)tst-absolute-zero-lib.so): New dependency.
($(objpfx)tst-absolute-zero: New dependency.
The only differences in ld.so are line numbers for asserts.
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
* elf/dl-addr.c (determine_info): Use ADDRIDX with DT_GNU_HASH.
* elf/dl-lookup.c (_dl_setup_hash): Likewise.
* elf/get-dynamic-info.h (elf_get_dynamic_info): Likewise.
This commit separates allocating and raising exceptions. This
simplifies catching and re-raising them because it is no longer
necessary to make a temporary, on-stack copy of the exception message.
In a reference to PR ld/19908 make ld.so respect symbol export classes
aka visibility and treat STV_HIDDEN and STV_INTERNAL symbols as local,
preventing such symbols from preempting exported symbols.
According to the ELF gABI[1] neither STV_HIDDEN nor STV_INTERNAL symbols
are supposed to be present in linked binaries:
"A hidden symbol contained in a relocatable object must be either
removed or converted to STB_LOCAL binding by the link-editor when the
relocatable object is included in an executable file or shared object."
"An internal symbol contained in a relocatable object must be either
removed or converted to STB_LOCAL binding by the link-editor when the
relocatable object is included in an executable file or shared object."
however some GNU binutils versions produce such symbols in some cases.
PR ld/19908 is one and we also have this note in scripts/abilist.awk:
so clearly there is linked code out there which contains such symbols
which is prone to symbol table misinterpretation, and it'll be more
productive if we handle this gracefully, under the Robustness Principle:
"be liberal in what you accept, and conservative in what you produce",
especially as this is a simple (STV_HIDDEN|STV_INTERNAL) => STB_LOCAL
mapping.
References:
[1] "System V Application Binary Interface - DRAFT - 24 April 2001",
The Santa Cruz Operation, Inc., "Symbol Table",
<http://www.sco.com/developers/gabi/2001-04-24/ch4.symtab.html>
* sysdeps/generic/ldsodefs.h
(dl_symbol_visibility_binds_local_p): New inline function.
* elf/dl-addr.c (determine_info): Treat hidden and internal
symbols as local.
* elf/dl-lookup.c (do_lookup_x): Likewise.
* elf/dl-reloc.c (RESOLVE_MAP): Likewise.
* elf/dl-lookup.c (_dl_lookup_symbol_x): Report error even if
skip_map != NULL.
* elf/tst-dlsym-error.c: New file.
* elf/Makefile (tests): Add tst-dlsym-error.
(tst-dlsym-error): Link against libdl.
prelink runs ld.so with the environment variable LD_TRACE_PRELINKING
set to dump the relocation type class from _dl_debug_bindings. prelink
has the following relocation type classes:
#define RTYPE_CLASS_VALID 8
#define RTYPE_CLASS_PLT (8|1)
#define RTYPE_CLASS_COPY (8|2)
#define RTYPE_CLASS_TLS (8|4)
where ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA has a conflict with
RTYPE_CLASS_TLS.
Since prelink only uses ELF_RTYPE_CLASS_PLT and ELF_RTYPE_CLASS_COPY
bits, we should clear the other bits when the DL_DEBUG_PRELINK bit is
set.
[BZ #19178]
* elf/dl-lookup.c (RTYPE_CLASS_VALID): New.
(RTYPE_CLASS_PLT): Likewise.
(RTYPE_CLASS_COPY): Likewise.
(RTYPE_CLASS_TLS): Likewise.
(_dl_debug_bindings): Use RTYPE_CLASS_TLS and RTYPE_CLASS_VALID
to set relocation type class for DL_DEBUG_PRELINK. Keep only
ELF_RTYPE_CLASS_PLT and ELF_RTYPE_CLASS_COPY bits for
DL_DEBUG_PRELINK.
With copy relocation, address of protected data defined in the shared
library may be external. When there is a relocation against the
protected data symbol within the shared library, we need to check if we
should skip the definition in the executable copied from the protected
data. This patch adds ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA and defines
it for x86. If ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA isn't 0, do_lookup_x
will skip the data definition in the executable from copy reloc.
[BZ #17711]
* elf/dl-lookup.c (do_lookup_x): When UNDEF_MAP is NULL, which
indicates it is called from do_lookup_x on relocation against
protected data, skip the data definion in the executable from
copy reloc.
(_dl_lookup_symbol_x): Pass ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA,
instead of ELF_RTYPE_CLASS_PLT, to do_lookup_x for
EXTERN_PROTECTED_DATA relocation against STT_OBJECT symbol.
* sysdeps/generic/ldsodefs.h * (ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA):
New. Defined to 4 if DL_EXTERN_PROTECTED_DATA is defined,
otherwise to 0.
* sysdeps/i386/dl-lookupcfg.h (DL_EXTERN_PROTECTED_DATA): New.
* sysdeps/i386/dl-machine.h (elf_machine_type_class): Set class
to ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA for R_386_GLOB_DAT.
* sysdeps/x86_64/dl-lookupcfg.h (DL_EXTERN_PROTECTED_DATA): New.
* sysdeps/x86_64/dl-machine.h (elf_machine_type_class): Set class
to ELF_RTYPE_CLASS_EXTERN_PROTECTED_DATA for R_X86_64_GLOB_DAT.
Convert all uses of __builtin_expect to __glibc_likely and
__glibc_unlikely. Most of these are trivial boolean expressions
but a few were not. In particular the use of __builtin_expect in
the switch expression in do_lookup_x has been removed. Verified
that there are no code changes on x86_64 and ARM aside from line
numbers.
ChangeLog:
2014-06-23 Will Newton <will.newton@linaro.org>
* elf/dl-lookup.c: Use __glibc_unlikely and __glibc_likely
rather than __builtin_expect.
undefined_msg is only used once contrary to the comment.
ChangeLog:
2014-06-23 Will Newton <will.newton@linaro.org>
* elf/dl-lookup.c (undefined_msg): Remove variable.
(_dl_lookup_symbol_x): Replace undefined_msg with string
literal.
Move handling of STB_GNU_UNIQUE symbols to a separate function
from do_lookup_x in order to make the code more readable.
The new function gets inlined with gcc 4.8 on ARM and the
do_lookup_x code becomes a few bytes smaller.
ChangeLog:
2014-06-23 Will Newton <will.newton@linaro.org>
* elf/dl-lookup.c (do_lookup_unique): New function.
(do_lookup_x): Move STB_GNU_UNIQUE handling code
to a separate function.
The nested function referred to has gone away so remove the
comment. Also move the variable declaration down to where other
variables of a similar lifetime are declared for clarity.
2014-04-03 Will Newton <will.newton@linaro.org>
* elf/dl-lookup.c (do_lookup_x): Remove comment
referring to nested function and move variable
declarations down to before first use.
While it may be argued that nested functions make the resulting
code easier to read, or worse to read the following two bugs
make it difficult to debug:
Bug 8300 - no local symbol information within nested or nesting
procedures
https://sourceware.org/bugzilla/show_bug.cgi?id=8300
Bug 53927 - wrong value for DW_AT_static_link
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53927
Until these are fixed I've made check_match a full function.
After they are fixed we can resume arguing about the merits
of nested functions on readability and maintenance.
MIPS has its own version of dl-lookup.c to deal with differences
between undefined symbol semantics in the PIC and non-PIC ABIs. This
is often liable to get out of date with respect to the generic file
(for example, the recent __builtin_expect changes didn't cover ports,
and it's not obvious to anyone changing dl-lookup.c that there would
be architecture-specific versions).
This patch adds a macro that dl-machine.h can define that is used in
the appropriate place in dl-lookup.c, so that MIPS no longer needs its
own version of that file.
Tested for mips64 that the only changes to disassembly of installed
shared libraries appear to be ld.so changes attributable to different
line numbers and paths in assertions.
* elf/dl-lookup.c (ELF_MACHINE_SYM_NO_MATCH): Define if not
already defined.
(do_lookup_x): Use ELF_MACHINE_SYM_NO_MATCH.
* sysdeps/mips/dl-lookup.c: Remove.
* sysdeps/mips/dl-machine.h (ELF_MACHINE_SYM_NO_MATCH): New macro.
Resolves: #15465
The program name may be unavailable if the user application tampers
with argc and argv[]. Some parts of the dynamic linker caters for
this while others don't, so this patch consolidates the check and
fallback into a single macro and updates all users.
* elf/rtld.c (dl_main): If DL_DEBUG_UNUSED is enabled, turn off
lazy binding.
* elf/dl-lookup (_dl_lookup_symbol_x): If DL_DEBUG_UNUSED, ignore
undefined symbol errors.
* elf/rtlc.c (dl_main): Skip VDSO when checking for unused
DT_NEEDED entries.
On some architectures the update of the l_used field in the lookup
functions races with setting the other bits in the bitfield. Simply
avoid this and optimize use of l_used in general.
SSE registers are used for passing parameters and must be preserved
in runtime relocations. This is inside ld.so enforced through the
tests in tst-xmmymm.sh. But the malloc routines used after startup
come from libc.so and can be arbitrarily complex. It's overkill
to save the SSE registers all the time because of that. These calls
are rare. Instead we save them on demand. The new infrastructure
put in place in this patch makes this possible and efficient.
There were several issues when the initial 31 entries hashtab filled up.
size * 3 <= tab->n_elements is always false, table can't have more elements
than its size. I assume from libiberty/hashtab.c this meant to be check for
3/4 full. Even after fixing that, _dl_higher_prime_number (31) apparently
returns 31, only _dl_higher_prime_number (32) returns 61. And, size
variable wasn't updated during reallocation, which means during reallocation
the insertion of the new entry was done into a wrong spot.
All this lead to a hang in ld.so, because a search with n_elements 31 size
31 wouldn't ever terminate.
References to unique symbols from copy relocations can only come
from executables which cannot be unloaded anyway. Optimize the
code to set the unload flag a bit.
Some symbols have to be identified process-wide by their name. This is
particularly important for some C++ features (e.g., class local static data
and static variables in inline functions). This cannot completely be
implemented with ELF functionality so far. The STB_GNU_UNIQUE binding
helps by ensuring the dynamic linker will always use the same definition for
all symbols with the same name and this binding.
The dl-lookup.c changes are needed for prelink (support in prelink
checked into SVN, tested for both i?86 and x86-64), dl-irel.h just
something I discovered by code inspection.
void * pointers instead of struct link_map **.
(_dl_scope_free): Change argument type to void *.
* include/link.h (struct link_map): Change type of l_reldeps
to struct link_map_reldeps, move l_reldepsact into that
struct too.
* elf/dl-deps.c: Include atomic.h.
(_dl_map_object_deps): Only change l->l_initfini when it is
fully populated, use _dl_scope_free for freeing it. Optimize
removal of libs from reldeps by using l_reserved flag, when
some removal is needed, allocate a new list instead of
reallocating and free the old with _dl_scope_free. Adjust
for l_reldeps and l_reldepsact changes.
* elf/dl-lookup.c (add_dependency): Likewise. Reorganize to allow
searching in l_initfini and l_reldeps without holding dl_load_lock.
* elf/dl-fini.c (_dl_sort_fini): Adjust for l_reldeps and
l_reldepsact changes.
* elf/dl-close.c (_dl_close_worker): Likewise.
* elf/dl-open.c (_dl_scope_free): Change argument type to void *.
* elf/dl-runtime.c (_dl_fixup, _dl_profile_fixup): Or in
DL_LOOKUP_GSCOPE_LOCK into flags after THREAD_GSCOPE_SET_FLAG ().
* elf/dl-sym.c (do_sym): Likewise.
* include/link.h (struct link_map): Add l_serial field.
* elf/dl-object.c (_dl_new_object): Initialize l_serial.
* elf/dl-lookup.c (add_dependency): Add flags argument.
Remember map->l_serial, if DL_LOOKUP_GSCOPE_LOCK is among
flags, use THREAD_GSCOPE_RESET_FLAG before and
THREAD_GSCOPE_SET_FLAG after
__rtld_lock_lock_recursive (GL(dl_load_lock)) to avoid deadlock.
Don't dereference map until it has been found on some list.
If map->l_serial changed, return -1.
2007-06-13 Jakub Jelinek <jakub@redhat.com>
* include/link.h: Don't include rtld-lowlevel.h.
(struct link_map): Remove l_scope_lock.
* sysdeps/generic/ldsodefs.h: Don't include rtld-lowlevel.h.
(_dl_scope_free_list): New field (variable) in _rtld_global.
(DL_LOOKUP_SCOPE_LOCK): Remove.
(_dl_scope_free): New prototype.
* elf/dl-runtime.c (_dl_fixup): Don't use __rtld_mrlock_*lock.
Don't pass DL_LOOKUP_SCOPE_LOCK to _dl_lookup_symbol_x.
(_dl_profile_fixup): Likewise.
* elf/dl-sym.c (do_sym): Likewise. Use wrapped _dl_lookup_symbol_x
whenever !RTLD_SINGLE_THREAD_P, use THREAD_GSCOPE_SET_FLAG and
THREAD_GSCOPE_RESET_FLAG around it.
* elf/dl-close.c (_dl_close_worker): Don't use
__rtld_mrlock_{change,done}. Call _dl_scope_free on the old
scope. Make sure THREAD_GSCOPE_WAIT () happens if any old
scopes were queued or if l_scope_mem has been abandoned.
* elf/dl-open.c (_dl_scope_free): New function.
(dl_open_worker): Use it. Don't use __rtld_mrlock_{change,done}.
* elf/dl-support.c (_dl_scope_free_list): New variable.
* elf/dl-lookup.c (add_dependency): Remove flags argument.
Remove DL_LOOKUP_SCOPE_LOCK handling.
(_dl_lookup_symbol_x): Adjust caller. Remove DL_LOOKUP_SCOPE_LOCK
handling.
* elf/dl-object.c (_dl_new_object): Don't use
__rtld_mrlock_initialize.
2007-06-19 Ulrich Drepper <drepper@redhat.com>
Nobody
Joseph Myers
Maciej W. Rozycki
H.J. Lu
Florian Weimer
Maciej W. Rozycki
Roland McGrath
Will Newton
Carlos O'Donell
Ondřej Bílka
Allan McRae
Marcus Shawcroft
Siddhesh Poyarekar
David S. Miller
Paul Eggert
Ulrich Drepper
Piotr Bury
Jim Meyering
Ulrich Drepper
Andreas Schwab
Jakub Jelinek