Re: [PATCH] rtld-audit.7: tfix

[Namhyung Kim <namhyung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Michael,

On Wed, Dec 02, 2015 at 05:14:47PM +0100, Michael Kerrisk (man-pages) wrote:
> Hello Namhyung Kim,
> 
> I need some explanation here. This is not a simple 
> typo fix, I believe. Why do you think the current text 
> is wrong?

Actually la_pltenter() is called regardless of the value of framesizep
but la_pltexit() is called only if la_pltenter() returns with non-zero
framesizep set.  I spent long time to figure out why la_pltexit() is
not called at all.

Quoting comments in glibc/sysdeps/x86_64/dl-trampoline.h:

  /* There's nothing in the frame size, so there
     will be no call to the _dl_call_pltexit. */

and

  /* At this point we need to prepare new stack for the function
     which has to be called.  We copy the original stack to a
     temporary buffer of the size specified by the 'framesize'
     returned from _dl_profile_fixup */


I think it's because it needs to preserve 'inregs' to be passed to
la_pltexit().

The _dl_profile_fixup() sets the '*framesizep' to maximum value of
what la_pltenter() sets.  Please see glibc/elf/dl-runtime.c file.

Thanks,
Namhyung


> 
> On 11/03/2015 01:18 AM, Namhyung Kim wrote:
> > Signed-off-by: Namhyung Kim <namhyung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> > ---
> >  man7/rtld-audit.7 | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/man7/rtld-audit.7 b/man7/rtld-audit.7
> > index d0f7563..643bc57 100644
> > --- a/man7/rtld-audit.7
> > +++ b/man7/rtld-audit.7
> > @@ -400,7 +400,7 @@ If different
> >  invocations for this symbol return different values,
> >  then the maximum returned value is used.
> >  The
> > -.BR la_pltenter ()
> > +.BR la_pltexit ()
> >  function is called only if this buffer is
> >  explicitly set to a suitable value.
> >  
> > 
> 
> 
> -- 
> Michael Kerrisk
> Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
> Linux/UNIX System Programming Training: http://man7.org/training/
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