[v2] dlsym: Add RTLD_PROBE to dlsym only probe symbol without add dependency.
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Commit Message
dlsym with RTLD_DEFAULT add dependency for target symbol, if program
use dlsym only to detect if a symbol exist, and will not use it.
this operation will make unable to dlclose so file containing target
symbol, add RTLD_PROBE to support symbol probe.
The reason why not useing struct link_map * as an argument to dlsym is
that there may be more than one same-named symbol in different so
files(provided by different vendors or components) in one process, and
by -Wl,-z,now,only the first symbol is needed, and we cannot be sure
which struct link_map* should be send to dlsym.
Signed-off-by: Wang Bing <wangbing6@huawei.com>
---
v2: fix code corruption
v1: https://public-inbox.org/libc-alpha/7cad26c73f5b4172bbcf570882bf9d3d@huawei.com/#R
---
dlfcn/dlfcn.h | 4 ++++
elf/Makefile | 1 +
elf/dl-sym.c | 13 +++++++++---
elf/tst-dlsym-rtld-probe.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 65 insertions(+), 3 deletions(-)
create mode 100644 elf/tst-dlsym-rtld-probe.c
Comments
* Wang Bing via Libc-alpha:
> diff --git a/elf/tst-dlsym-rtld-probe.c b/elf/tst-dlsym-rtld-probe.c
> new file mode 100644
> index 0000000000..c72ceaa182
> --- /dev/null
> +++ b/elf/tst-dlsym-rtld-probe.c
> @@ -0,0 +1,50 @@
> +/* Test RTLD_PROBE for dlsym.
> + Copyright (C) 2022-2022 Free Software Foundation, Inc.
> + 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
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <dlfcn.h>
> +#include <gnu/lib-names.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <support/check.h>
> +#include <support/xdlfcn.h>
> +
> +static int
> +do_test (void)
> +{
> + int *iptr;
> + int ret;
> + void *handle;
> +
> + handle = dlopen (LIBM_SO, RTLD_LAZY);
> + TEST_VERIFY (handle == NULL);
> + iptr = (int *)dlsym (RTLD_PROBE, "finite"); // get sym but not call --detect if symbol exist
> + ret = dlclose (handle);
> + TEST_VERIFY (ret != 0);
> + ret = 0;
> +
> + handle = dlopen (LIBM_SO, RTLD_LAZY);
> + TEST_VERIFY (handle == NULL);
> + iptr = (int *)dlsym (RTLD_DEFAULT, "finite"); // get sym and keep
> + ret = dlcose (handle);
> + TEST_VERIFY (ret == 0);
> + return 0;
> +}
> +
> +
> +#include <support/test-driver.c>
I tried to fix the test case to work stand-alone, and with RTLD_DEFAULT:
#include <dlfcn.h>
#include <err.h>
#include <gnu/lib-names.h>
#include <stddef.h>
int
main (void)
{
void *handle = dlopen (LIBM_SO, RTLD_LAZY);
if (handle == NULL)
errx (1, dlerror ());
void *p = dlsym (RTLD_DEFAULT, "finite");
if (p == NULL)
errx (1, dlerror ());
if (dlclose (handle) != 0)
errx (1, dlerror ());
if (dlopen (LIBM_SO, RTLD_LAZY | RTLD_NOLOAD) != NULL)
errx (1, "libm not unloaded");
return 0;
}
It does not show that unloading is blocked: RTLD_NOLOAD subsequently
fails. Furthermore, the LD_DEBUG=all output indicates that unloading
happens before the return from main (before the ELF destructors are
called):
268899: symbol=dlclose; lookup in file=./a.out [0]
268899: symbol=dlclose; lookup in file=/lib64/libc.so.6 [0]
268899: binding file ./a.out [0] to /lib64/libc.so.6 [0]: normal symbol `dlclose' [GLIBC_2.34]
268899:
268899: calling fini: /lib64/libm.so.6 [0]
268899:
268899:
268899: file=/lib64/libm.so.6 [0]; destroying link map
268899:
268899: file=libm.so.6 [0]; dynamically loaded by ./a.out [0]
268899: find library=libm.so.6 [0]; searching
268899: search cache=/etc/ld.so.cache
268899: trying file=/lib64/libm.so.6
268899:
268899:
268899: calling fini: [0]
Please post a test case that demonstrates the problem you are trying to
fix.
Thanks,
Florian
@@ -49,6 +49,10 @@ typedef long int Lmid_t;
is returned. */
#define RTLD_DEFAULT ((void *) 0)
+/* If only find sym in the global scope, but will not use it, do not
+ set sym dependency. */
+# define RTLD_PROBE ((void *) -2l)
+
__BEGIN_DECLS
/* Open the shared object FILE and map it in; return a handle that can be
@@ -472,6 +472,7 @@ tests += \
unload7 \
unload8 \
valgrind-test \
+ tst-dlsym-rtld-probe \
# tests
tests-cxx = \
tst-dlopen-nodelete-reloc \
@@ -92,10 +92,17 @@ do_sym (void *handle, const char *name, void *who,
/* Link map of the caller if needed. */
struct link_map *match = NULL;
- if (handle == RTLD_DEFAULT)
+ int def_flags;
+
+ if (handle == RTLD_DEFAULT || handle == RTLD_PROBE)
{
match = _dl_sym_find_caller_link_map (caller);
+ def_flags = flags
+ if (def_flags == RTLD_DEFAULT) {
+ def_flags |= DL_LOOKUP_ADD_DEPENDENCY;
+ }
+
/* Search the global scope. We have the simple case where
we look up in the scope of an object which was part of
the initial binary. And then the more complex part
@@ -104,7 +111,7 @@ do_sym (void *handle, const char *name, void *who,
if (RTLD_SINGLE_THREAD_P)
result = GLRO(dl_lookup_symbol_x) (name, match, &ref,
match->l_scope, vers, 0,
- flags | DL_LOOKUP_ADD_DEPENDENCY,
+ def_flags,
NULL);
else
{
@@ -113,7 +120,7 @@ do_sym (void *handle, const char *name, void *who,
args.map = match;
args.vers = vers;
args.flags
- = flags | DL_LOOKUP_ADD_DEPENDENCY | DL_LOOKUP_GSCOPE_LOCK;
+ = def_flags | DL_LOOKUP_GSCOPE_LOCK;
args.refp = &ref;
THREAD_GSCOPE_SET_FLAG ();
new file mode 100644
@@ -0,0 +1,50 @@
+/* Test RTLD_PROBE for dlsym.
+ Copyright (C) 2022-2022 Free Software Foundation, Inc.
+ 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <dlfcn.h>
+#include <gnu/lib-names.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <support/check.h>
+#include <support/xdlfcn.h>
+
+static int
+do_test (void)
+{
+ int *iptr;
+ int ret;
+ void *handle;
+
+ handle = dlopen (LIBM_SO, RTLD_LAZY);
+ TEST_VERIFY (handle == NULL);
+ iptr = (int *)dlsym (RTLD_PROBE, "finite"); // get sym but not call --detect if symbol exist
+ ret = dlclose (handle);
+ TEST_VERIFY (ret != 0);
+ ret = 0;
+
+ handle = dlopen (LIBM_SO, RTLD_LAZY);
+ TEST_VERIFY (handle == NULL);
+ iptr = (int *)dlsym (RTLD_DEFAULT, "finite"); // get sym and keep
+ ret = dlcose (handle);
+ TEST_VERIFY (ret == 0);
+ return 0;
+}
+
+
+#include <support/test-driver.c>