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Date: Sun, 9 Jul 2017 11:23:23 +0200
From: u-uy74@...ey.se
To: musl@...ts.openwall.com
Subject: Re: Question about setting argv[0] when manually using
dynamic linker
On Tue, Jul 04, 2017 at 04:58:11PM -0400, Rich Felker wrote:
> On Sun, Jul 02, 2017 at 07:36:19PM +0200, u-uy74@...ey.se wrote:
> > On Wed, May 17, 2017 at 12:24:28PM -0400, Rich Felker wrote:
> > > Perhaps adding an option like --argv0=foo would be
> > > appropriate.
> >
> > Is this option being considered to introduce?
> Yes, adding it.
Thanks again, it makes some "unsolvable" cases work as needed.
OTOH when applying this in practice, I noticed that a slightly
different behaviour would be very handy: if the linker could
supply its own argv[0] as the one for the program to run.
This would fit nicely into the framework where we already set argv[0]
anyway, in the same way for both statically and dynamically linked
programs. (The only exception so far would be a hypothetical need to
pass on the value "ldd" as argv[0], then --argv0=ldd would save the day)
Otherwise we have to set the dynloader --argv0 argument per binary
which is of course possible but remarkably less convenient,
among others because this setting is dynloader-specific, while
otherwise our tools are libc- and dynamic vs static agnostic.
IOW as long as the loader itself does not rely on its argv[0]
too much, plainly passing on argv[0] is a very practical means to
handle the programs like busybox and gcc transparently.
What about always passing on the loader argv[0] unless --argv0 is present?
This will not matter for programs which do not analyze argv[0]
and will not make it worse for programs which do.
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1388,7 +1388,7 @@
kernel_mapped_dso(&app);
} else {
int fd;
- char *ldname = argv[0];
+ char *ldname = replace_argv0 = argv[0];
size_t l = strlen(ldname);
if (l >= 3 && !strcmp(ldname+l-3, "ldd")) ldd_mode = 1;
argv++;
or even
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1322,7 +1322,7 @@
size_t aux[AUX_CNT], *auxv;
size_t i;
char *env_preload=0;
- char *replace_argv0=0;
+ char *replace_argv0=argv[0];
size_t vdso_base;
int argc = *sp;
char **argv = (void *)(sp+1);
@@ -1567,7 +1567,7 @@
debug.state = 0;
_dl_debug_state();
- if (replace_argv0) argv[0] = replace_argv0;
+ argv[0] = replace_argv0;
errno = 0;
Otherwise may be something like this:
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1409,6 +1409,7 @@
else if (*argv) env_preload = *argv++;
} else if (!memcmp(opt, "argv0", 5)) {
if (opt[5]=='=') replace_argv0 = opt+6;
+ else if (opt[5]=='^') replace_argv0 = ldname;
else if (opt[5]) *argv = 0;
else if (*argv) replace_argv0 = *argv++;
} else {
to instead introduce an extra --argv0^ option ?
Regards,
Rune
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