ld.so: add an --argv0 option
Commit Message
Hi,
a few years ago there was an effort for adding --argv0 option:
https://sourceware.org/legacy-ml/libc-alpha/2016-04/msg00576.html.
I made the old patch actual for version 2.31.9000, added a test case and
changelog.
2020-07-22 Vincent Mihalkovic <vmihalko@redhat.com>
* elf/Makefile: added argv0 test case, Modified.
* elf/rtld.c: added --argv0 option, Modified.
* elf/argv0test.c: test case, New file.
* elf/tst-rtld-argv0.sh: test case, New file.
Comments
* Vincent Mihalkovic via Libc-alpha:
> a few years ago there was an effort for adding --argv0 option:
> https://sourceware.org/legacy-ml/libc-alpha/2016-04/msg00576.html.
> I made the old patch actual for version 2.31.9000, added a test case and
> changelog.
Many shells support “exec -a” to get a similar effect. The advantage is
that this does not perturb the argument vector layout. Given that, I
think promoting --argv0 would merely introduce further compatibility
issues.
Thanks,
Florian
Hi,
Sorry, I forgot to CC the libc-alpha mailing-list on my reply.
We do not need the option for shell scripting, where it is indeed not
needed,
as you say. We are developing a tool for running dynamic analysis tools on
RPM packages fully automatically. The tool appends custom linker flags
while
executing the %build section of RPMs to make the binaries use our custom ELF
interpreter. While running the %check section, the interpreter takes care
of
running the binaries built in %build through the selected dynamic analyzer
in
a way that does not break the testing framework. For this to work, we need
to run dynamic linker explicitly. There is currently no way to preserve the
original argv[0], which some programs are sensitive to. This unnecessarily
breaks the tests running in %check of some RPM packages.
An experimental implementation of the custom ELF interpreter is available
here:
https://github.com/kdudka/cswrap/pull/2
thanks for considering this idea,
vincent mihalkovic
On Wed, Jul 22, 2020 at 11:00 AM Florian Weimer <fweimer@redhat.com> wrote:
> * Vincent Mihalkovic via Libc-alpha:
>
> > a few years ago there was an effort for adding --argv0 option:
> > https://sourceware.org/legacy-ml/libc-alpha/2016-04/msg00576.html.
> > I made the old patch actual for version 2.31.9000, added a test case and
> > changelog.
>
> Many shells support “exec -a” to get a similar effect. The advantage is
> that this does not perturb the argument vector layout. Given that, I
> think promoting --argv0 would merely introduce further compatibility
> issues.
>
> Thanks,
> Florian
>
>
* Vincent Mihalkovic:
> Sorry, I forgot to CC the libc-alpha mailing-list on my reply.
And I think this won't make it to the list due to the HTML filters, so
here's a full quote:
> We do not need the option for shell scripting, where it is indeed not
> needed, as you say. We are developing a tool for running dynamic
> analysis tools on RPM packages fully automatically. The tool appends
> custom linker flags while executing the %build section of RPMs to make
> the binaries use our custom ELF interpreter. While running the %check
> section, the interpreter takes care of running the binaries built in
> %build through the selected dynamic analyzer in a way that does not
> break the testing framework. For this to work, we need to run dynamic
> linker explicitly. There is currently no way to preserve the original
> argv[0], which some programs are sensitive to. This unnecessarily
> breaks the tests running in %check of some RPM packages.
>
> An experimental implementation of the custom ELF interpreter is available
> here:
>
> https://github.com/kdudka/cswrap/pull/2
>
> thanks for considering this idea,
> vincent mihalkovic
I was wrong about this, and it is not possible to get the desired
behavior using “exec -a”. The question remains if just updating the
pointer is sufficient in this context, or if a more elaborate copying
operation is needed to preserve the expected semantics of the argument
vector.
I guest we could add --argv0 now (well, after the 2.32 release), and if
it's incompatible with some applications, we can perhaps tweak it later.
Thanks,
Florian
@@ -210,7 +210,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
tst-filterobj tst-filterobj-dlopen tst-auxobj tst-auxobj-dlopen \
tst-audit14 tst-audit15 tst-audit16 \
tst-single_threaded tst-single_threaded-pthread \
- tst-tls-ie tst-tls-ie-dlmopen
+ tst-tls-ie tst-tls-ie-dlmopen \
+ argv0test
# reldep9
tests-internal += loadtest unload unload2 circleload1 \
neededtest neededtest2 neededtest3 neededtest4 \
@@ -414,7 +415,7 @@ endif
ifeq (yes,$(build-shared))
ifeq ($(run-built-tests),yes)
tests-special += $(objpfx)tst-pathopt.out $(objpfx)tst-rtld-load-self.out \
- $(objpfx)tst-rtld-preload.out
+ $(objpfx)tst-rtld-preload.out $(objpfx)argv0test.out
endif
tests-special += $(objpfx)check-textrel.out $(objpfx)check-execstack.out \
$(objpfx)check-wx-segment.out \
@@ -1796,3 +1797,11 @@ $(objpfx)tst-tls-ie-dlmopen.out: \
$(objpfx)tst-tls-ie-mod6.so
$(objpfx)tst-tls-surplus: $(libdl)
+
+ARGV0 = test-argv0
+$(objpfx)argv0test.out: tst-rtld-argv0.sh $(objpfx)ld.so \
+ $(objpfx)argv0test
+ $(SHELL) $< $(objpfx)ld.so $(objpfx)argv0test \
+ '$(test-wrapper-env)' '$(run_program_env)' \
+ '$(rpath-link)' '$(ARGV0)' > $@; \
+ $(evaluate-test)
new file mode 100644
@@ -0,0 +1,13 @@
+#include <stdio.h> // for printf
+#include <string.h> // for strcmp
+
+
+int main( int argc, char *argv[] ) {
+ int result = strcmp( argv[0], "test-argv0");
+
+ printf ("argv[0] = %s, strcmp( argv[0], \"test-argv0\" ) = %d, %s\n", \
+ argv[0], result, !result ? "ok" : "wrong");
+
+ return result;
+
+}
@@ -1202,6 +1202,8 @@ dl_main (const ElfW(Phdr) *phdr,
installing it. */
rtld_is_main = true;
+ char *argv0 = NULL;
+
/* Note the place where the dynamic linker actually came from. */
GL(dl_rtld_map).l_name = rtld_progname;
@@ -1259,6 +1261,14 @@ dl_main (const ElfW(Phdr) *phdr,
else if (! strcmp (_dl_argv[1], "--preload") && _dl_argc > 2)
{
preloadarg = _dl_argv[2];
+ _dl_skip_args += 2;
+ _dl_argc -= 2;
+ _dl_argv += 2;
+ }
+ else if (! strcmp (_dl_argv[1], "--argv0") && _dl_argc > 2)
+ {
+ argv0 = _dl_argv[2];
+
_dl_skip_args += 2;
_dl_argc -= 2;
_dl_argv += 2;
@@ -1292,7 +1302,8 @@ of this helper program; chances are you did not intend to run this program.\n\
--inhibit-rpath LIST ignore RUNPATH and RPATH information in object names\n\
in LIST\n\
--audit LIST use objects named in LIST as auditors\n\
- --preload LIST preload objects named in LIST\n");
+ --preload LIST preload objects named in LIST\n\
+ --argv0 STRING set argv[0] to STRING before running\n");
++_dl_skip_args;
--_dl_argc;
@@ -1384,6 +1395,11 @@ of this helper program; chances are you did not intend to run this program.\n\
break;
}
#endif
+
+ /* Set the argv[0] string now that we've processed the executable. */
+ if (argv0 != NULL) {
+ _dl_argv[0] = argv0;
+ }
}
else
{
new file mode 100755
@@ -0,0 +1,37 @@
+#!/bin/sh
+# Test --argv0 argument ld.so.
+# Copyright (C) 2019-2020 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/>.
+
+set -e
+
+rtld=$1
+test_program=$2
+test_wrapper_env=$3
+run_program_env=$4
+library_path=$5
+argv0=$6
+
+echo "# [${test_wrapper_env}] [${run_program_env}] [$rtld] [--library-path]" \
+ "[$library_path] [--argv0] [$argv0] [$test_program]"
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --library-path "$library_path" \
+ --argv0 "$argv0" $test_program 2>&1 && rc=0 || rc=$?
+echo "# exit status $rc"
+
+exit $rc