From: Paul Pluzhnikov <ppluzhnikov@google.com>
To: archer@sourceware.org
Subject: Re: Improved linker-debugger interface
Date: Thu, 26 May 2011 17:37:00 -0000 [thread overview]
Message-ID: <BANLkTimn8XXk3nf86zh4ELtV_-FDYugsuQ@mail.gmail.com> (raw)
In-Reply-To: <20110525153649.GB3149@redhat.com>
Gary,
On Wed, May 25, 2011 at 8:36 AM, Gary Benson <gbenson@redhat.com> wrote:
> The solution I'm proposing is this:
It's great that you are working on this, thanks!
You might wish to consider the following points, which (AFAICT) you are
not currently addressing.
1. Stripped binaries.
There is a DT_DEBUG entry pointing to _dl_debug_state (set by ld-linux)
You might want to have a new dynamic tag, pointing to
_dl_debug_state_extended(), so the debugger would be able to track
shared libs using the new mechanism even when everything is stripped.
2. In-process debuggers.
There are many use cases for "self-aware" binaries. For example,
google-perftools collects profiling info with stack traces, and getting
a stack trace requires that you know which DSOs are loaded into the
process.
The current interface is very hostile to such debuggers, as
_dl_debug_state
A) is called directly by libc (so there is no way to interpose it), and
B) compiles down to a single 'ret', so there is no way to place a patch
on top of it.
This leads to all kinds of suboptimal solutions (such as scanning
/proc/self/maps; which doesn't work if /proc is not mounted).
A patch to make _dl_debug_state indirect through r_debug.r_brk has
been rejected:
https://bugzilla.redhat.com/show_bug.cgi?id=70407
Perhaps co-operation with "in-process" debuggers would be more acceptable
for a new interface?
Thanks,
--
Paul Pluzhnikov
next prev parent reply other threads:[~2011-05-26 17:37 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-25 15:37 Gary Benson
2011-05-25 18:21 ` Tom Tromey
2011-05-26 17:02 ` Gary Benson
2011-05-26 17:25 ` Tom Tromey
2011-05-26 17:37 ` Paul Pluzhnikov [this message]
2011-05-26 17:47 ` Tom Tromey
2011-05-26 21:07 ` Tom Tromey
2011-05-31 16:25 ` Gary Benson
2011-05-31 19:46 ` Tom Tromey
2011-05-31 20:41 ` Paul Pluzhnikov
2011-05-31 20:46 ` Tom Tromey
2011-05-31 21:05 ` Paul Pluzhnikov
2011-06-02 23:56 ` Tom Tromey
2011-06-07 16:58 ` Jan Kratochvil
2011-06-08 10:56 ` Gary Benson
2011-06-01 1:24 Frank Ch. Eigler
2011-06-02 23:56 ` Tom Tromey
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