problems with dlsym() on MIPS, looking for advice

problems with dlsym() on MIPS, looking for advice

[Chris Friesen]

I think this is a userspace/toolchain issue, so if that's offtopic for 
this list please let me know of a better resource.

We're using glibc 2.3.6 and gcc 3.4.4.  We've got some library code 
(that gets preloaded for debugging) something like this:

ee_sigaction_fptr = dlsym(RTLD_DEFAULT, "sigaction"); 
   if (ee_sigaction_fptr == sigaction) 
      	ee_sigaction_fptr = dlsym(RTLD_NEXT, "sigaction");

We have declared our own sigaction procedure which is extern in this 
code.  On non-MIPS arches (powerpc, x86, x86_64) the RTLD_DEFAULT call 
returns the address of our external procedure and the RTLD_NEXT call 
returns the real sigaction address in its appropriate library.

On MIPS, the DEFAULT returns the address of this libraries undefined 
symbol for the extern and NEXT returns our external procedure.  Putting 
in a second RTLD_NEXT call returned the real sigaction address.

This worked for most procedures we are looking for. However, during 
booting, we have an app that uses a specific library which has an extern 
for sigaction as well and now in the preloaded code we need a fourth 
call to dlsym to skip that one.

We tried recoding the above debug code to do one DEFAULT call and a loop 
of NEXT calls until it returns NULL.  It didn't.  It just kept returning 
the last pointer all the time. 


Has anyone seen anything like this?  Is there a known issue with dlsym() 
and certain toolchains?  (Maybe something like 
"http://busybox.net/lists/uclibc/2007-January/017150.html"?)


Any help you can provide would be appreciated.

Thanks,

Chris

Re: do-lookup.h regarding to mips/dlsym and libstdc++

[Daniel Jacobowitz]

On Tue, Jan 29, 2008 at 01:32:20PM +0900, Yoriko Komatsuzaki wrote:
> Because even though UNDEF symbol is found, 
> it can process as global symbol for the rare occasion.
> 
> This phenomena is showed only in mips. When libstdc++ is linked in
> proior libc, the malloc's entry in libstdc++ MIPS.stubs table seemed to
> be recognized as the malloc global symbol ...
> 
> How do you feel about it?

On Mon, May 26, 2008 at 11:51:56AM -0600, Chris Friesen wrote:
> On MIPS, the DEFAULT returns the address of this libraries undefined  
> symbol for the extern and NEXT returns our external procedure.  Putting  
> in a second RTLD_NEXT call returned the real sigaction address.
>
> This worked for most procedures we are looking for. However, during  
> booting, we have an app that uses a specific library which has an extern  
> for sigaction as well and now in the preloaded code we need a fourth call 
> to dlsym to skip that one.

Hi folks,

This bug is fixed as a by-product of support for non-PIC MIPS
executables.  Either Richard's patch or CodeSourcery's, applied to
glibc, should suffice.  It'll be another week or two at least before
they're applied to CVS, but in the mean time you can find them here:

http://sourceware.org/ml/binutils/2008-06/msg00280.html
http://sourceware.org/ml/binutils/2008-07/msg00008.html

-- 
Daniel Jacobowitz
CodeSourcery

Re: do-lookup.h regarding to mips/dlsym and libstdc++

[Yoriko Komatsuzaki]

Thank you for your reply.
I will do the checking.

---
Yoriko Komatsuzaki (yoriko@sm.sony.co.jp)
System Software Development Department
Common Technology Division
Technology Development Group
Sony Corporation

> On Tue, Jan 29, 2008 at 01:32:20PM +0900, Yoriko Komatsuzaki wrote:
> > Because even though UNDEF symbol is found, 
> > it can process as global symbol for the rare occasion.
> > 
> > This phenomena is showed only in mips. When libstdc++ is linked in
> > proior libc, the malloc's entry in libstdc++ MIPS.stubs table seemed to
> > be recognized as the malloc global symbol ...
> > 
> > How do you feel about it?
> 
> On Mon, May 26, 2008 at 11:51:56AM -0600, Chris Friesen wrote:
> > On MIPS, the DEFAULT returns the address of this libraries undefined  
> > symbol for the extern and NEXT returns our external procedure.  Putting  
> > in a second RTLD_NEXT call returned the real sigaction address.
> >
> > This worked for most procedures we are looking for. However, during  
> > booting, we have an app that uses a specific library which has an extern  
> > for sigaction as well and now in the preloaded code we need a fourth call 
> > to dlsym to skip that one.
> 
> Hi folks,
> 
> This bug is fixed as a by-product of support for non-PIC MIPS
> executables.  Either Richard's patch or CodeSourcery's, applied to
> glibc, should suffice.  It'll be another week or two at least before
> they're applied to CVS, but in the mean time you can find them here:
> 
> http://sourceware.org/ml/binutils/2008-06/msg00280.html
> http://sourceware.org/ml/binutils/2008-07/msg00008.html
> 
> -- 
> Daniel Jacobowitz
> CodeSourcery
>