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Re: [PATCH] ld.so: Support moving versioned symbols between sonames [BZ #24741]
On 6/27/19 1:13 PM, Florian Weimer wrote:
> * Yann Droneaud:
>
>>> diff --git a/elf/Makefile b/elf/Makefile
>>> index 27a2fa8c14..76b0565054 100644
>>> --- a/elf/Makefile
>>> +++ b/elf/Makefile
>>> @@ -191,7 +191,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
>>> tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
>>> tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
>>> tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
>>> - tst-unwind-ctor tst-unwind-main tst-audit13
>>> + tst-unwind-ctor tst-unwind-main tst-audit13 \
>>> + tst-sonamemove tst-sonamemove-dlopen
>>
>> tst-sonamemove could be name tst-sonamemove-link to make obvious the
>> difference with -dlopen.
>
> Good idea.
>
>>> +$(objpfx)tst-sonamemove-dlopen: $(libdl)
>>> +$(objpfx)tst-sonamemove.out: \
>>> + $(objpfx)tst-sonamemove-runmod1.so \
>>> + $(objpfx)tst-sonamemove-runmod2.so
>>> +
>>
>> The last three lines duplicate those above.
>
> Fixed.
>
>>> +/* moved_function is linked against tst-sonamemove-runmod1.so, but the
>>> + actual implementation is in tst-sonamemove-runmod1.so. */
>>
>> I found this comment unclear. tst-sonamemove is linked against tst-
>> sonamemove-linkmod1.so, which has tst-sonamemove-runmod1.so soname.
>> When tst-sonamemove is run, tst-sonamemove-runmod1.so is loaded, which
>> imply loading tst-sonamemove-runmod2.so as a dependency. tst-
>> sonamemove-runmod2.so is where move_function's implementation is.
>
> I tried to explain this more explictly:
>
> /* At link time, moved_function is bound to the symbol version
> SONAME_MOVE in tst-sonamemove-runmod1.so, using the
> tst-sonamemove-linkmod1.so stub object.
>
> At run time, the process loads the real tst-sonamemove-runmod1.so,
> which depends on tst-sonamemove-runmod2.so.
> tst-sonamemove-runmod1.so does not define moved_function, but
> tst-sonamemove-runmod2.so does.
>
> The net effect is that the versioned symbol
> moved_function@SONAME_MOVE moved from the soname
> tst-sonamemove-linkmod1.so at link time to the soname
> tst-sonamemove-linkmod2.so at run time. */
>
> Thanks,
> Florian
>
> ld.so: Support moving versioned symbols between sonames [BZ #24741]
>
> This change should be fully backwards-compatible because the old
> code aborted the load if a soname mismatch was encountered
> (instead of searching further for a matching symbol). This means
> that no different symbols are found.
>
> The soname check was explicitly disabled for the skip_map != NULL
> case. However, this only happens with dl(v)sym and RTLD_NEXT,
> and those lookups do not come with a verneed entry that could be used
> for the check.
>
> The error check was already explicitly disabled for the skip_map !=
> NULL case, that is, when dl(v)sym was called with RTLD_NEXT. But
> _dl_vsym always sets filename in the struct r_found_version argument
> to NULL, so the check was not active anyway. This means that
> symbol lookup results for the skip_map != NULL case do not change,
> either.
I am strong proponent of this change. I think it goes in the right
direction. While symbol binding to a version is important, that version
may need to be moved to another shared library and that flexibility is
important during shuffling of the implementation in glibc or any other
project. It could eventually allow us to split glibc into *further*
smaller libraries, or unify it into a single hyper-optimized library/loader,
whichever we pick, it helps.
It leaves the open question: Why was the binding so specific? I don't
have a good answer for that, and I think we should clarify the language
of the ELF symbol versioning specification for this change. I have gone
through the specification again and I see nothing that would require
this behaviour.
I have dropped Ulrich's text here in our wiki:
https://sourceware.org/glibc/wiki/ELFSymbolVersioning
There is a hint here:
~~~
These tests have to be recursively performed for all objects and their
dependencies. This way it is possible to recognize libraries which
are too old and don't contain all the symbols or contain incompatible
implementations. Without this kind of test one could end up with
runtime errors which don't provide helpful information.
~~~
Notice the wording "don't contain all the symbols", which is actually
the case here when you *move* a symbol from one DSO to another, you
no longer get an error that the library may be incomplete. It seems
overly restrictive to me, and doesn't match the semantics of symbol
interposition where you can get part of the implementation in a
preloaded library and the rest in the original library. Functionally
interposition supports the behaviour we want which is to have another
library provide those symbols, and this change simply makes it possible
to do this without LD_PRELOAD or changes in search ordering.
Can we update our wiki page to reflect what glibc actually implements
for symbol versioning? We could put it in git, or work with HJ to get
it upstream into the ABI docs, or just edit the wiki (for now).
> 2019-06-27 Florian Weimer <fweimer@redhat.com>
>
> [BZ #24741]
> * elf/dl-lookup.c (do_lookup_x): Do not fail if there is a soname
> mismatch in a versioned symbol reference.
> (_dl_lookup_symbol_x): Do not report soname mismatch failures.
> * elf/Makefile [$(build-shared)] (tests): Add tst-sonamemove-link,
> tst-sonamemove-dlopen.
> (module-names): Add tst-sonamemove-linkmod1,
> tst-sonamemove-runmod1, tst-sonamemove-runmod2.
> (LDFLAGS-tst-sonamemove-linkmod1.so): Set.
> (LDFLAGS-tst-sonamemove-runmod1.so): Likewise.
> (LDFLAGS-tst-sonamemove-runmod2.so): Likewise.
> (tst-sonamemove-runmod1.so): Link against
> tst-sonamemove-runmod2.so.
> (tst-sonamemove-link): Link against tst-sonamemove-linkmod1.so.
> (tst-sonamemove-link.out): Depend on tst-sonamemove-runmod1.so,
> tst-sonamemove-runmod2.so.
> (tst-sonamemove-dlopen): Link with -ldl.
> (tst-sonamemove-dlopen.out): Likewise.
> * elf/tst-sonamemove-link.c: New file.
> * elf/tst-sonamemove-dlopen.c: Likewise.
> * elf/tst-sonamemove-linkmod1.c: Likewise.
> * elf/tst-sonamemove-linkmod1.map: Likewise.
> * elf/tst-sonamemove-runmod1.c: Likewise.
> * elf/tst-sonamemove-runmod1.map: Likewise.
> * elf/tst-sonamemove-runmod2.c: Likewise.
> * elf/tst-sonamemove-runmod2.map: Likewise.
> * support/xdlfcn.h (xdlvsym): Declare function.
> * support/xdlfcn.c (xdlvsym): Define funciton.
>
OK for master if:
- we document the change in our copy of the standard describing symbol
versioning.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> diff --git a/NEWS b/NEWS
> index 8a2fecef47..8cea9f5825 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -34,6 +34,12 @@ Major new features:
> pointer subtraction within the allocated object, where results might
> overflow the ptrdiff_t type.
>
> +* The dynamic linker no longer refuses to load objects which reference
> + versioned symbols whose implementation has moved to a different soname
> + since the object has been linked. The old error message, symbol
> + FUNCTION-NAME, version SYMBOL-VERSION not defined in file DSO-NAME with
> + link time reference, is gone.
OK. I actually like that the binding information tells you *where* the original
linkage was from, since that information may be important some day.
> +
> Deprecated and removed features, and other changes affecting compatibility:
>
> * The functions clock_gettime, clock_getres, clock_settime,
> diff --git a/elf/Makefile b/elf/Makefile
> index 27a2fa8c14..a3eefd1b1f 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -191,7 +191,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
> tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
> tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
> tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
> - tst-unwind-ctor tst-unwind-main tst-audit13
> + tst-unwind-ctor tst-unwind-main tst-audit13 \
> + tst-sonamemove-link tst-sonamemove-dlopen
OK. Two new tests.
> # reldep9
> tests-internal += loadtest unload unload2 circleload1 \
> neededtest neededtest2 neededtest3 neededtest4 \
> @@ -281,7 +282,8 @@ modules-names = testobj1 testobj2 testobj3 testobj4 testobj5 testobj6 \
> tst-nodelete-dlclose-dso tst-nodelete-dlclose-plugin \
> tst-main1mod tst-libc_dlvsym-dso tst-absolute-sym-lib \
> tst-absolute-zero-lib tst-big-note-lib tst-unwind-ctor-lib \
> - tst-audit13mod1
> + tst-audit13mod1 tst-sonamemove-linkmod1 \
> + tst-sonamemove-runmod1 tst-sonamemove-runmod2
OK. Three new DSOs.
> # Most modules build with _ISOMAC defined, but those filtered out
> # depend on internal headers.
> modules-names-tests = $(filter-out ifuncmod% tst-libc_dlvsym-dso tst-tlsmod%,\
> @@ -1410,6 +1412,28 @@ $(objpfx)tst-audit13.out: $(objpfx)tst-audit13mod1.so
> LDFLAGS-tst-audit13mod1.so = -Wl,-z,lazy
> tst-audit13-ENV = LD_AUDIT=$(objpfx)tst-audit13mod1.so
>
> +# tst-sonamemove links against an older implementation of the library.
> +LDFLAGS-tst-sonamemove-linkmod1.so = \
> + -Wl,--version-script=tst-sonamemove-linkmod1.map \
> + -Wl,-soname,tst-sonamemove-runmod1.so
OK. Same soname.
> +LDFLAGS-tst-sonamemove-runmod1.so = -Wl,--no-as-needed \
> + -Wl,--version-script=tst-sonamemove-runmod1.map \
> + -Wl,-soname,tst-sonamemove-runmod1.so
OK. Same soname.
> +LDFLAGS-tst-sonamemove-runmod2.so = \
> + -Wl,--version-script=tst-sonamemove-runmod2.map \
> + -Wl,-soname,tst-sonamemove-runmod2.so
OK. Different soname.
> +$(objpfx)tst-sonamemove-runmod1.so: $(objpfx)tst-sonamemove-runmod2.so
> +# Link against the link module, but depend on the run-time modules
> +# for execution.
> +$(objpfx)tst-sonamemove-link: $(objpfx)tst-sonamemove-linkmod1.so
> +$(objpfx)tst-sonamemove-link.out: \
> + $(objpfx)tst-sonamemove-runmod1.so \
> + $(objpfx)tst-sonamemove-runmod2.so
OK, Build the dsos before running the test.
> +$(objpfx)tst-sonamemove-dlopen: $(libdl)
> +$(objpfx)tst-sonamemove-dlopen.out: \
> + $(objpfx)tst-sonamemove-runmod1.so \
> + $(objpfx)tst-sonamemove-runmod2.so
OK. likewise.
> +
> # Override -z defs, so that we can reference an undefined symbol.
> # Force lazy binding for the same reason.
> LDFLAGS-tst-latepthreadmod.so = \
> diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
> index e3f42a1efb..eb23cca4e3 100644
> --- a/elf/dl-lookup.c
> +++ b/elf/dl-lookup.c
> @@ -536,11 +536,7 @@ do_lookup_x (const char *undef_name, uint_fast32_t new_hash,
> }
>
> skip:
> - /* If this current map is the one mentioned in the verneed entry
> - and we have not found a weak entry, it is a bug. */
> - if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
> - && __glibc_unlikely (_dl_name_match_p (version->filename, map)))
> - return -1;
> + ;
OK.
An audit of _dl_name_match_p() which is predominantly used for this purpose
shows callers in dl-load.c, dl-lookup.c, dl-misc.c, dl-version.c, and rtld.c.
I found one questionable assert in dl-lookup.c
99 if (version != NULL)
100 {
101 if (__glibc_unlikely (verstab == NULL))
102 {
103 /* We need a versioned symbol but haven't found any. If
104 this is the object which is referenced in the verneed
105 entry it is a bug in the library since a symbol must
106 not simply disappear.
107
108 It would also be a bug in the object since it means that
109 the list of required versions is incomplete and so the
110 tests in dl-version.c haven't found a problem.*/
111 assert (version->filename == NULL
112 || ! _dl_name_match_p (version->filename, map));
113
114 /* Otherwise we accept the symbol. */
Why would we assert here? Can we reasonably handle this error?
If it is the object referenced in verneed then version->filename != NULL
and so the assert triggers? That seems overly restrictive, and I expect
we don't get here because earlier dl-version.c checks fail. I'm not asking
you to cleanup this code, but it does beg the next question.
What happens if you move the last versioned symbol out of a library?
Are you allowed to stop using the version script in the library that
has zero versioned symbols? I think the answer is "No." Because we
still check that all libraries provide the version sets that they
had at link time? Is that still OK?
Everything else looks OK.
> }
> while (++i < n);
>
> @@ -810,34 +806,10 @@ _dl_lookup_symbol_x (const char *undef_name, struct link_map *undef_map,
>
> /* Search the relevant loaded objects for a definition. */
> for (size_t start = i; *scope != NULL; start = 0, ++scope)
> - {
> - int res = do_lookup_x (undef_name, new_hash, &old_hash, *ref,
> - ¤t_value, *scope, start, version, flags,
> - skip_map, type_class, undef_map);
> - if (res > 0)
> - break;
> -
> - if (__glibc_unlikely (res < 0) && skip_map == NULL)
> - {
> - /* Oh, oh. The file named in the relocation entry does not
> - contain the needed symbol. This code is never reached
> - for unversioned lookups. */
> - assert (version != NULL);
> - const char *reference_name = undef_map ? undef_map->l_name : "";
> - struct dl_exception exception;
> - /* XXX We cannot translate the message. */
> - _dl_exception_create_format
> - (&exception, DSO_FILENAME (reference_name),
> - "symbol %s version %s not defined in file %s"
> - " with link time reference%s",
> - undef_name, version->name, version->filename,
> - res == -2 ? " (no version symbols)" : "");
> - _dl_signal_cexception (0, &exception, N_("relocation error"));
> - _dl_exception_free (&exception);
> - *ref = NULL;
> - return 0;
> - }
> - }
> + if (do_lookup_x (undef_name, new_hash, &old_hash, *ref,
> + ¤t_value, *scope, start, version, flags,
> + skip_map, type_class, undef_map) != 0)
> + break;
OK. This removes the well known code that does this check from _dl_lookup_symbol_x.
I didn't know about the case in do_lookup_x.
>
> if (__glibc_unlikely (current_value.s == NULL))
> {
> diff --git a/elf/tst-sonamemove-dlopen.c b/elf/tst-sonamemove-dlopen.c
> new file mode 100644
> index 0000000000..c496705044
> --- /dev/null
> +++ b/elf/tst-sonamemove-dlopen.c
> @@ -0,0 +1,35 @@
> +/* Check that a moved versioned symbol can be found using dlsym, dlvsym.
OK.
> + Copyright (C) 2019 Free Software Foundation, Inc.
OK.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +#include <stddef.h>
> +#include <support/check.h>
> +#include <support/xdlfcn.h>
> +
> +static int
> +do_test (void)
> +{
> + /* tst-sonamemove-runmod1.so does not define moved_function, but it
> + depends on tst-sonamemove-runmod2.so, which does. */
OK.
> + void *handle = xdlopen ("tst-sonamemove-runmod1.so", RTLD_NOW);
> + TEST_VERIFY (xdlsym (handle, "moved_function") != NULL);
> + TEST_VERIFY (xdlvsym (handle, "moved_function", "SONAME_MOVE") != NULL);
OK.
> +
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/elf/tst-sonamemove-link.c b/elf/tst-sonamemove-link.c
> new file mode 100644
> index 0000000000..4bc3bf32f8
> --- /dev/null
> +++ b/elf/tst-sonamemove-link.c
> @@ -0,0 +1,41 @@
> +/* Check that a versioned symbol can move from one library to another.
OK.
> + Copyright (C) 2019 Free Software Foundation, Inc.
OK.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +/* At link time, moved_function is bound to the symbol version
> + SONAME_MOVE in tst-sonamemove-runmod1.so, using the
> + tst-sonamemove-linkmod1.so stub object.
OK.
> +
> + At run time, the process loads the real tst-sonamemove-runmod1.so,
> + which depends on tst-sonamemove-runmod2.so.
> + tst-sonamemove-runmod1.so does not define moved_function, but
> + tst-sonamemove-runmod2.so does.
OK.
> +
> + The net effect is that the versioned symbol
> + moved_function@SONAME_MOVE moved from the soname
> + tst-sonamemove-linkmod1.so at link time to the soname
> + tst-sonamemove-linkmod2.so at run time. */
OK.
> +void moved_function (void);
> +
> +static int
> +do_test (void)
> +{
> + moved_function ();
> + return 0;
OK.
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/elf/tst-sonamemove-linkmod1.c b/elf/tst-sonamemove-linkmod1.c
> new file mode 100644
> index 0000000000..b8a354e5e3
> --- /dev/null
> +++ b/elf/tst-sonamemove-linkmod1.c
> @@ -0,0 +1,25 @@
> +/* Link interface for (lack of) soname matching in versioned symbol refs.
> + Copyright (C) 2019 Free Software Foundation, Inc.
OK.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +/* This function moved from tst-sonamemove-runmod1.so. This module is
> + intended for linking only, to simulate an old application which was
> + linked against an older version of the library. */
> +void
> +moved_function (void)
> +{
> +}
OK.
> diff --git a/elf/tst-sonamemove-linkmod1.map b/elf/tst-sonamemove-linkmod1.map
> new file mode 100644
> index 0000000000..8fe5904018
> --- /dev/null
> +++ b/elf/tst-sonamemove-linkmod1.map
> @@ -0,0 +1,3 @@
> +SONAME_MOVE {
> + global: moved_function;
> +};
OK.
> diff --git a/elf/tst-sonamemove-runmod1.c b/elf/tst-sonamemove-runmod1.c
> new file mode 100644
> index 0000000000..5c409e2289
> --- /dev/null
> +++ b/elf/tst-sonamemove-runmod1.c
> @@ -0,0 +1,23 @@
> +/* Run-time module whose moved_function moved to a library dependency.
> + Copyright (C) 2019 Free Software Foundation, Inc.
OK.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +/* Dummy function to add the required symbol version. */
> +void
> +other_function (void)
> +{
> +}
OK. Ah, so you do need a dummy function to preserve the required version
set or we still get another error? I expect the answer is "Yes" and that
we're not entirely willing to remove this requirement. We're happy to move
symbols, but what about keeping the original symbol set intact? Would we
relax that in a subsequent patch?
> diff --git a/elf/tst-sonamemove-runmod1.map b/elf/tst-sonamemove-runmod1.map
> new file mode 100644
> index 0000000000..2ea81c6e6f
> --- /dev/null
> +++ b/elf/tst-sonamemove-runmod1.map
> @@ -0,0 +1,3 @@
> +SONAME_MOVE {
> + global: other_function;
> +};
OK.
> diff --git a/elf/tst-sonamemove-runmod2.c b/elf/tst-sonamemove-runmod2.c
> new file mode 100644
> index 0000000000..b5e482eff5
> --- /dev/null
> +++ b/elf/tst-sonamemove-runmod2.c
> @@ -0,0 +1,24 @@
> +/* Run-time module with the actual implementation of moved_function.
> + Copyright (C) 2019 Free Software Foundation, Inc.
OK.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <http://www.gnu.org/licenses/>. */
> +
> +/* In the test scenario, this function was originally in
> + tst-sonamemove-runmod1.so. */
> +void
> +moved_function (void)
> +{
> +}
OK.
> diff --git a/elf/tst-sonamemove-runmod2.map b/elf/tst-sonamemove-runmod2.map
> new file mode 100644
> index 0000000000..8fe5904018
> --- /dev/null
> +++ b/elf/tst-sonamemove-runmod2.map
> @@ -0,0 +1,3 @@
> +SONAME_MOVE {
> + global: moved_function;
> +};
OK.
> diff --git a/support/xdlfcn.c b/support/xdlfcn.c
> index b2e5c21134..11fe4896d1 100644
> --- a/support/xdlfcn.c
> +++ b/support/xdlfcn.c
> @@ -51,6 +51,26 @@ xdlsym (void *handle, const char *symbol)
> return sym;
> }
>
> +void *
> +xdlvsym (void *handle, const char *symbol, const char *version)
> +{
> + /* Clear any pending errors. */
> + dlerror ();
> +
> + void *sym = dlvsym (handle, symbol, version);
> +
> + if (sym == NULL)
> + {
> + const char *error = dlerror ();
> + if (error != NULL)
> + FAIL_EXIT1 ("error: dlvsym: %s\n", error);
> + /* If there was no error, we found a NULL symbol. Return the
> + NULL value in this case. */
> + }
> +
> + return sym;
> +}
OK.
> +
> void
> xdlclose (void *handle)
> {
> diff --git a/support/xdlfcn.h b/support/xdlfcn.h
> index c9cd810a8a..7f8d4930fc 100644
> --- a/support/xdlfcn.h
> +++ b/support/xdlfcn.h
> @@ -27,6 +27,7 @@ __BEGIN_DECLS
> void *xdlopen (const char *filename, int flags);
> void *xdlmopen (Lmid_t lmid, const char *filename, int flags);
> void *xdlsym (void *handle, const char *symbol);
> +void *xdlvsym (void *handle, const char *symbol, const char *version);
> void xdlclose (void *handle);
>
> __END_DECLS
>
OK.
--
Cheers,
Carlos.