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Re: [PATCH] Initialize _r_debug for static applications.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Cc: Jan Kratochvil <jan dot kratochvil at redhat dot com>, "Maciej W. Rozycki" <macro at codesourcery dot com>, Roland McGrath <roland at hack dot frob dot com>
- Date: Thu, 10 Apr 2014 20:33:32 -0400
- Subject: Re: [PATCH] Initialize _r_debug for static applications.
- Authentication-results: sourceware.org; auth=none
- References: <5347321E dot 2060802 at redhat dot com>
On 04/10/2014 08:06 PM, Carlos O'Donell wrote:
> With Maciej's great work on reducing the difference between
> static and dyanmic executables, and with the addition of
> a functional main link map in static exectuables we can now
> usefully initialize _r_debug for static applications. This
> will allow future debuggers the ability to coalesce code
> paths which previously had to have special cases for static
> v.s. dyanmic.
>
> It also fixes this particular use case where gdb would like
> a consistent way to find the application link map for looking
> up TLS variables in both static and dynamic applications:
> https://www.sourceware.org/ml/libc-help/2014-03/msg00024.html
>
> The discussion touches on the fact that without _r_debug the
> debugger has to make various assupmtions while using
> libthread_db that contrains the implementation.
>
> This patch initializes the debug infrastructure during
> LIBC_START_MAIN, but only for static applications, by
> calling `_dl_debug_initialize (0, LM_ID_BASE)'. We pass 0 as
> the ldbase because it's a static application, and the runtime
> address of the loader doesn't matter. We pass LM_ID_BASE because
> we want to load, by default, the base link map, and that's what
> really matters.
>
> Tested on x86_64 with no regressions.
>
> Jan reports this works and that gdb can be patched to use
> _r_debug to access TLS variables in static applications
> while still using the current libthread_db calls normally
> used for dynamic applications.
>
> This removes one more difference between static and dynamic
> applications.
>
> Note: This does not attempt to cleanup the -Wundef warning
> for SHARED, which I am looking to fix in another patch so
> we still use `#ifndef SHARED' (Makeconfig needs to be fixed
> to use -DSHARED=0 and -DSHARED=1 IMO to make this work correctly).
>
> OK to checkin?
>
> Cheers,
> Carlos.
>
> 2014-04-10 Carlos O'Donell <carlos@redhat.com>
>
[BZ #16831]
> * csu/libc-start.c (LIBC_START_MAIN) [!SHARED]: Call
> _dl_debug_initialize.
Filed 16831 for user visible change to _r_debug interface.
https://sourceware.org/bugzilla/show_bug.cgi?id=16831
Cheers,
Carlos.