[Bug libc/12575] New: dlopen RTLD_NOW does not apply to GNU-IFUNCs

[Bug libc/12575] New: dlopen RTLD_NOW does not apply to GNU-IFUNCs

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12575

           Summary: dlopen RTLD_NOW does not apply to GNU-IFUNCs
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: jan.kratochvil@redhat.com


`-Wl,-z,now' works and the GNU-IFUNC resolver is called before `main'.

But RTLD_NOW returns handle and GNU-IFUNC gets called only after `dlsym'.
Even if the executable calling dlopen(, RTLD_NOW) uses -Wl,-z,-now.

The first part of the test below is correct:
+ ./mc
f
main

But this part prints:
+ ./mcd
dlsym
f

while I expect:
+ ./mcd
f
dlsym

This behavior determines how the glibc Bug 2328 should be resolved in GDB.


cat >lc.c <<EOH
#include <stdio.h>
static int
fi (int a)
{
  return a + 1;
}
asm (".type f, @gnu_indirect_function");
int (*
f (void)) (int a)
{
  puts ("f");
  return fi;
}
EOH
cat >mc.c <<EOH
#include <stdio.h>
extern int f (int a);
int
main (void)
{
  puts ("main");
  return f (-1);
}
EOH
cat >mcd.c <<EOH
#include <stdio.h>
#include <dlfcn.h>
int
main (void)
{
  void *h = dlopen ("./lc.so", RTLD_NOW);
  puts ("dlsym");
  int (*fp) (int a) = (int (*) (int a)) dlsym (h, "f");
  return fp (-1);
}
EOH
gcc -o lc.so lc.c -Wall -g -shared -fPIC; gcc -o mc mc.c -Wall -g -Wl,-z,now
./lc.so; gcc -o mcd mcd.c -Wall -g -Wl,-z,now -ldl; (set -x; ./mc; ./mcd)

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug libc/12575] dlopen RTLD_NOW does not apply to GNU-IFUNCs

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12575

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-fedora15-linux-gnu
               Host|                            |x86_64-fedora15-linux-gnu
             Blocks|                            |2328

--- Comment #1 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-03-13 10:16:28 UTC ---
Tested on Fedora 15:
glibc-2.13.90-6.i686
glibc-2.13.90-6.x86_64

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug libc/12575] dlopen RTLD_NOW does not apply to GNU-IFUNCs

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12575

Ulrich Drepper <drepper.fsp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |WORKSFORME

--- Comment #2 from Ulrich Drepper <drepper.fsp at gmail dot com> 2011-05-12 03:09:03 UTC ---
There is nothing to change in the dynamic linker.

When you dynamically load the DSO this doesn't magically make a relocation
appear.  In your test, the symbol f doesn't have any relocation attached to it
and this is correct.  This is really the expected behavior.  Without a
relocation or returning the symbol address (as in dlsym) there is no place to
store the result of the ifunc function call.

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug libc/12575] dlopen RTLD_NOW does not apply to GNU-IFUNCs

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12575

--- Comment #3 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-06-02 13:13:06 UTC ---
I agree now, there is no <f@plt> stub anywhere in the dlopen case, thanks.

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.

[Bug libc/12575] dlopen RTLD_NOW does not apply to GNU-IFUNCs

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=12575

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

-- 
You are receiving this mail because:
You are on the CC list for the bug.