svn commit: r270803 - head/libexec/rtld-elf

[Konstantin Belousov]

On Fri, Aug 29, 2014 at 09:57:31AM -0500, Bryan Drewery wrote:
> On 8/29/2014 5:44 AM, Konstantin Belousov wrote:
> > Author: kib
> > Date: Fri Aug 29 10:44:58 2014
> > New Revision: 270803
> > URL: http://svnweb.freebsd.org/changeset/base/270803
> > 
> > Log:
> >   Document the whole settings needed to build a debug version of rtld.
> >   
> >   Sponsored by:	The FreeBSD Foundation
> >   MFC after:	3 days
> > 
> > Modified:
> >   head/libexec/rtld-elf/Makefile
> > 
> > Modified: head/libexec/rtld-elf/Makefile
> > ==============================================================================
> > --- head/libexec/rtld-elf/Makefile	Fri Aug 29 10:43:56 2014	(r270802)
> > +++ head/libexec/rtld-elf/Makefile	Fri Aug 29 10:44:58 2014	(r270803)
> > @@ -1,5 +1,9 @@
> >  # $FreeBSD$
> >  
> > +# Use the following command to build local debug version of dynamic
> > +# linker:
> > +# make DEBUG_FLAGS=-g DEBUG=-DDEBUG MK_TESTS=no all
> > +
> >  .include <src.opts.mk>
> >  MK_SSP=		no
> >  
> > 
> 
> How difficult would it be to allow DEBUG to be set during runtime like
> GNU's can with LD_DEBUG? I have found GNU's LD_DEBUG to be very useful
> for userland debugging, especially when using dlopen(3).
> 
> We have LD_DEBUG environment variable but it only prints if built with
> -DDEBUG.
> 
> Is there a concern about performance by enabling this based only on
> environment?

I am sure that nobody evaluated the performance consequences of
unconditionally compiling the debugging stuff in. I am sure that the
ld-elf.so.1 size will increase.

The reason why nobody cares to evaluate and enable this stuff by default
is that the debugging output is very ad-hoc. I found it almost useless
in both the content and amount of data it outputs. The reason why I
enable it for my work on ld-elf is that I insert my own dbg() calls for
debugging (and usually remove them before the commit since they add even
more verbosity useless for general public consumption).

I find the combination of the ELF dumping tools like readelf and
objdump, together with gdb (-g) and custom dbg() statement (slighly
glorified printf debugging) most adequate combination to debug rtld.

After the long preamble. What use do you have for LD_DEBUG ? If it is
possible to formalize and tailor the debugging output for real users
needs, I am all for making it available unconditionally from LD_DEBUG
knob. The significants part of the current dbg() statements would be
removed or require more agressive settings to become active.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 819 bytes
Desc: not available
URL: <http://lists.freebsd.org/pipermail/svn-src-all/attachments/20140829/b1c105cf/attachment.sig>