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From: Florian Weimer via Libc-alpha <libc-alpha@sourceware.org>
To: Carlos O'Donell via Libc-alpha <libc-alpha@sourceware.org>
Cc: Pedro Alves <palves@redhat.com>,
	Conan C Huang <conhuang@cisco.com>,
	Florian Weimer <fw@deneb.enyo.de>,
	Jeremy Stenglein <jstengle@cisco.com>,
	xe-linux-external@cisco.com
Subject: Re: [RFC PATCH 3/3] add r_debug multiple namespaces support
Date: Mon, 29 Jun 2020 10:51:06 +0200	[thread overview]
Message-ID: <87y2o61chx.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <8a15bd93-e4cc-a3bc-f902-5b3e701ec4e3@redhat.com> (Carlos O'Donell via Libc-alpha's message of "Sun, 28 Jun 2020 08:34:32 -0400")

* Carlos O'Donell via Libc-alpha:

>>> I'm not sure it would work to version _r_debug, since the debugger
>>> is using DT_DEBUG and we only get to put one value in that
>>> .dynamic entry.
>> 
>> The symbol version is needed to avoid problems due to copy relocations
>> if the symbol is referenced directly from the main program.  Without
>> that, the object could be truncated.  It's not a debugger
>> compatibility feature.
>
> Correct, but this violates *how* you're supposed to use _r_debug.

If it is possible to link against it, we need to add the new symbol
version, in my opinion.

> In the dynamic case it is different. The symbol should be looked up
> via DT_DEBUG only which always points to the library-local address
> of the data object (and the most recent version). In effect this
> bypasses the COPY relocation?

How is this supposed to work if the dynamic linker does contain
DT_DEBUG?

I only observe DT_DEBUG in PIE binaries, but since the dynamic loader is
mapped at a random address even for ET_EXEC main programs, there must be
some other mechanism to locate it.

Thanks,
Florian


  reply	other threads:[~2020-06-29  9:42 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-26 19:32 [RFC PATCH 3/3] add r_debug multiple namespaces support Daniel Walker via Libc-alpha
2020-06-26 21:05 ` Florian Weimer via Libc-alpha
2020-06-26 21:19   ` Carlos O'Donell via Libc-alpha
2020-06-26 21:24     ` Florian Weimer via Libc-alpha
2020-06-26 21:44       ` Carlos O'Donell via Libc-alpha
2020-06-27  9:34         ` Florian Weimer
2020-06-28 12:34           ` Carlos O'Donell via Libc-alpha
2020-06-29  8:51             ` Florian Weimer via Libc-alpha [this message]
2021-07-23 23:38               ` H.J. Lu via Libc-alpha
2021-07-27 17:39                 ` Daniel Walker via Libc-alpha
2021-07-27 18:14                   ` H.J. Lu via Libc-alpha
2021-07-28 15:15                     ` H.J. Lu via Libc-alpha
2021-07-28 15:44                       ` Daniel Walker via Libc-alpha
2021-07-28 17:14                         ` H.J. Lu via Libc-alpha
2021-07-28 19:02                           ` Daniel Walker via Libc-alpha
2021-07-28 20:04                             ` H.J. Lu via Libc-alpha
2021-08-02  4:24                               ` RFC: Add DT_GNU_DEBUG H.J. Lu via Libc-alpha
2021-08-02  5:22                                 ` Florian Weimer via Libc-alpha
2021-08-02 13:10                                   ` H.J. Lu via Libc-alpha
2021-08-03 16:39                                     ` Daniel Walker via Libc-alpha
2021-08-03 18:08                                       ` H.J. Lu via Libc-alpha
2021-08-03 20:04                                         ` Daniel Walker via Libc-alpha
2021-08-03 18:12                                       ` Florian Weimer via Libc-alpha
2021-08-03 18:23                                         ` H.J. Lu via Libc-alpha
2021-08-03 20:13                                           ` Florian Weimer via Libc-alpha
2021-08-03 20:21                                             ` H.J. Lu via Libc-alpha
2021-08-09 14:32                                               ` RFC: 2 choices of DT_XXX for dlmopen H.J. Lu via Libc-alpha
2021-08-09 17:16                                                 ` Daniel Walker via Libc-alpha
2021-08-15  0:33                                                   ` [PATCH] Extend struct r_debug to support multiple namespaces H.J. Lu via Libc-alpha
2021-08-16 16:20                                                     ` Daniel Walker via Libc-alpha
2021-08-17  1:07                                                       ` H.J. Lu via Libc-alpha
2020-06-27  1:21       ` [RFC PATCH 3/3] add r_debug multiple namespaces support Daniel Walker (danielwa) via Libc-alpha

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