ld.so: add an --argv0 option
Commit Message
Sometimes when you run a program you want the argv[0] string passed to
the app to be different than the actual path you used to load it. We
can't do this today with invoking via ld.so which can be limiting --
some programs like to inspect their argv[0] and make decisions as to
how it should (re)exec itself or helper tools. For example, clang and
gcc both do argv[0] inspection to support relocatable toolchains.
---
elf/rtld.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
Comments
* Mike Frysinger:
> Sometimes when you run a program you want the argv[0] string passed to
> the app to be different than the actual path you used to load it. We
> can't do this today with invoking via ld.so which can be limiting --
> some programs like to inspect their argv[0] and make decisions as to
> how it should (re)exec itself or helper tools. For example, clang and
> gcc both do argv[0] inspection to support relocatable toolchains.
Interesting idea. I think it's sufficiently to include this, but it
needs a ChangeLog entry and a test case.
On 23 Apr 2016 14:21, Florian Weimer wrote:
> * Mike Frysinger:
> > Sometimes when you run a program you want the argv[0] string passed to
> > the app to be different than the actual path you used to load it. We
> > can't do this today with invoking via ld.so which can be limiting --
> > some programs like to inspect their argv[0] and make decisions as to
> > how it should (re)exec itself or helper tools. For example, clang and
> > gcc both do argv[0] inspection to support relocatable toolchains.
>
> Interesting idea. I think it's sufficiently to include this, but it
> needs a ChangeLog entry and a test case.
for the test, seems like i'll have to write a small C file that just
displays its argv, and then another shell script which runs the ldso
against that simple program and checks the output. unless anyone has
a simpler idea.
-mike
* Mike Frysinger:
> On 23 Apr 2016 14:21, Florian Weimer wrote:
>> * Mike Frysinger:
>> > Sometimes when you run a program you want the argv[0] string passed to
>> > the app to be different than the actual path you used to load it. We
>> > can't do this today with invoking via ld.so which can be limiting --
>> > some programs like to inspect their argv[0] and make decisions as to
>> > how it should (re)exec itself or helper tools. For example, clang and
>> > gcc both do argv[0] inspection to support relocatable toolchains.
>>
>> Interesting idea. I think it's sufficiently to include this, but it
>> needs a ChangeLog entry and a test case.
>
> for the test, seems like i'll have to write a small C file that just
> displays its argv, and then another shell script which runs the ldso
> against that simple program and checks the output. unless anyone has
> a simpler idea.
You'll need the shell script wrapper.
Supplying the expected value in another argument, with some prefix and
suffix character, and comparing argv[0] to the extracted orignal
argument, is likely simpler than writing argv[0] to standard output
and reading it back from the shell script.
@@ -796,6 +796,8 @@ 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;
@@ -850,6 +852,14 @@ dl_main (const ElfW(Phdr) *phdr,
_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;
+ }
else
break;
@@ -878,7 +888,8 @@ of this helper program; chances are you did not intend to run this program.\n\
variable LD_LIBRARY_PATH\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");
+ --audit LIST use objects named in LIST as auditors\n\
+ --argv0 STRING set argv[0] to STRING before running\n");
++_dl_skip_args;
--_dl_argc;
@@ -971,6 +982,10 @@ 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
{