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Date:      Thu, 21 May 2020 09:03:44 -0700
From:      John Baldwin <jhb@FreeBSD.org>
To:        Mark Johnston <markj@freebsd.org>, Konstantin Belousov <kostikbel@gmail.com>
Cc:        Antoine Brodin <antoine@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head@freebsd.org
Subject:   Re: svn commit: r361303 - in head: lib/libc/gen libexec/rtld-elf sys/sys
Message-ID:  <c7fce441-692e-e4d6-64cb-ae86ef13c6cb@FreeBSD.org>
In-Reply-To: <20200521151248.GA85681@raichu>
References:  <202005202208.04KM8QPA020707@repo.freebsd.org> <CAALwa8mXfJZyRQ-Gx684mgoeTDZs14tEP26rJNqvh_rEiY18=Q@mail.gmail.com> <20200521134152.GE64045@kib.kiev.ua> <20200521151248.GA85681@raichu>

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On 5/21/20 8:12 AM, Mark Johnston wrote:
> On Thu, May 21, 2020 at 04:41:52PM +0300, Konstantin Belousov wrote:
>> On Thu, May 21, 2020 at 03:02:07PM +0200, Antoine Brodin wrote:
>>> On Thu, May 21, 2020 at 12:08 AM Konstantin Belousov <kib@freebsd.org> wrote:
>>>>
>>>> Author: kib
>>>> Date: Wed May 20 22:08:26 2020
>>>> New Revision: 361303
>>>> URL: https://svnweb.freebsd.org/changeset/base/361303
>>>>
>>>> Log:
>>>>   Change the samantic of struct link_map l_addr member.
>>>>
>>>>   It previously returned the object map base address, while all other
>>>>   ELF operating systems return load offset, i.e. the difference between
>>>>   map base and the link base.
>>>>
>>>>   Explain the meaning of the field in the man page.
>>>>
>>>>   Stop filling the mips-only l_offs member, which is apparently unused.
>>>>
>>>>   PR:   246561
>>>>   Requested by: Damjan Jovanovic <damjan.jov@gmail.com>
>>>>   Reviewed by:  emaste, jhb, cem (previous version)
>>>>   Sponsored by: The FreeBSD Foundation
>>>>   MFC after:    1 week
>>>>   Differential revision:        https://reviews.freebsd.org/D24918
>>>>
>>>> Modified:
>>>>   head/lib/libc/gen/dlinfo.3
>>>>   head/libexec/rtld-elf/rtld.c
>>>>   head/sys/sys/link_elf.h
>>>
>>> Hi,
>>>
>>> After this commit,  some ports fail to build with signal 11.
>>> For instance lang/perl5.30 fails to build with default options (DTRACE on)
>>> Disabling the DTRACE option makes it able to build again.
>>>
>> I see, thank you for reporting.
>>
>> So drti.c:dtrace_dof_init() does read l_addr, and the dtrace code assumes
>> that l_addr is the base, not relocbase.
>>
>> Mark, was dofhp_addr initialization changed comparing to Solaris ?
> 
> It appears it has been the same since DTrace was imported.  illumos
> still has similar code.
> 
> Note that drti.o is linked into any executable and shlib that defines
> static probes, so the ABI change affects more than just dtrace(1).
> Would it be possible to define a new value for RTLD_DI_LINKMAP, and
> preserve the old behaviour for the old value?

I think a bigger question is if Solaris/illumos treat l_addr as mapbase
(absolute address) or relocbase (relative address).  In the discussion
in the phabricator I had assumed that all other OS's treated l_addr as
the relative offset (relocbase).  Does the code for illumos assume an
absolute address or does it assume a relative address in l_addr?

-- 
John Baldwin



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