Re: Question about _dl_debug_state and new glibc

[Daniel Jacobowitz <drow at false dot org>]

On Mon, Oct 11, 2004 at 09:13:41PM +0200, Mark Kettenis wrote:
>    Date: Mon, 11 Oct 2004 13:55:25 -0400
>    From: Daniel Jacobowitz <drow@false.org>
> 
>    On Mon, Oct 11, 2004 at 10:46:47AM -0700, Kevin Buettner wrote:
>    > On Mon, 11 Oct 2004 10:22:07 -0700
>    > Randolph Chung <randolph@tausq.org> wrote:
>    > 
>    > > I've been away from gdb for a bit, so hopefully this is not something
>    > > simple I missed while I've been away :)
>    > > 
>    > > It appears that newer versions of glibc now marks the _dl_debug_state
>    > > function as hidden, making it not visible to gdb. This breaks the
>    > > solib tracking code in solib-svr4.c.....
>    > > 
>    > > Looking at the docs, it looks like the "proper" way for gdb to do this
>    > > is to look up the r_debug symbol and use the r_brk member to locate 
>    > > _dl_debug_state's address. is there any particular reason why we don't
>    > > do this in gdb?
> 
>    Only for static executables usually; for dynamic executables it's
>    supposed to be DT_DEBUG if that's available.  Same difference.
> 
> Hey wake up Daniel.  Static executables don't have shared libraries.

Oddly enough, in glibc they can - and often do.  There's a static
version of the runtime linker included, and things like dlopen work -
and internal libc functionality like NSS (gethostname, etc.) and gconv
use it.

Also, there are architectures where DT_DEBUG is missing.  I think MIPS
may be one.  Or maybe I'm misremembering this bit.

> I suppose this is just something that has never been completely
> implemented.  Somehow I think the dynamic linker was supposed to trap
> just after initializing r_debug and setting DT_DEBUG if it was being
> traced, perhaps if it noticed that DT_DEBUG was set to some special
> value by the debugger.  Perhaps we'll know when "Open Solaris" is
> released.

Makes sense to me.  Do any of the BSDs support using r_debug this way,
or do they export _dl_debug_state also?

>    I see it hasn't been exported since March.  Blech.
> 
> So we should ask the glibc developers to unhide _dl_debug_state.

I agree.

-- 
Daniel Jacobowitz