From: Tom Tromey <tromey@redhat.com>
To: Pedro Alves <palves@redhat.com>
Cc: gdb-patches@sourceware.org
Subject: Re: [PATCH 2/3] relocate the entry point addess when used
Date: Mon, 13 Jan 2014 20:46:00 -0000 [thread overview]
Message-ID: <8738kr1ug8.fsf@fleche.redhat.com> (raw)
In-Reply-To: <52CD5129.7090003@redhat.com> (Pedro Alves's message of "Wed, 08 Jan 2014 13:22:49 +0000")
>>>>> "Pedro" == Pedro Alves <palves@redhat.com> writes:
Tom> I think the existing code here is wrong. It computes the entry point
Tom> address directly from the BFD, not applying any runtime offsets.
Tom> However, then objfile_relocate1 passes this address to find_pc_section
Tom> -- which does use the offsets . So, it seems to me that the current
Tom> code can only find the correct address by luck.
Pedro> It's twisted, but I don't think it's luck. You can convince yourself
Pedro> it works by debugging a PIE, and trying a backtrace past main
Pedro> ("set backtrace past-main" will then trigger the code to stop the
Pedro> backtrace at the entry point), or doing "info files" (shows the entry).
Well, what I don't understand is that most addresses in dwarf2read.c are
offset:
baseaddr = ANOFFSET (objfile->section_offsets, SECT_OFF_TEXT (objfile));
... however this is not done for the entry point, which comes directly
from the BFD:
objfile->per_bfd->ei.entry_point = bfd_get_start_address (objfile->obfd);
I suppose there is some other invariant ensuring that the entry point is
only computed when all the objfile offsets are zero. This part is not
obvious to me.
[...]
Pedro> This is assuming osect ends up NULL after iterating over all.
Pedro> It's violating the abstraction of the macro. And, actually,
Pedro> it's wrong, showing exactly why such assumptions are a bad idea:
Sorry about that, I'll fix it up locally.
Tom
next prev parent reply other threads:[~2014-01-13 20:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-06 20:30 [PATCH 0/3] move entry point info to the per-BFD object Tom Tromey
2014-01-06 20:30 ` [PATCH 1/3] change solib-frv to use entry_point_address_query Tom Tromey
2014-01-08 13:23 ` Pedro Alves
2014-01-06 20:30 ` [PATCH 2/3] relocate the entry point addess when used Tom Tromey
2014-01-08 13:22 ` Pedro Alves
2014-01-13 20:46 ` Tom Tromey [this message]
2014-01-15 11:42 ` Pedro Alves
2014-01-15 17:59 ` Tom Tromey
2014-01-15 18:02 ` Pedro Alves
2014-01-06 20:30 ` [PATCH 3/3] move the entry point info into the per-bfd object Tom Tromey
2014-01-08 13:30 ` Pedro Alves
2014-01-13 20:51 ` Tom Tromey
2014-01-15 18:01 ` [PATCH 0/3] move entry point info to the per-BFD object Tom Tromey
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