svn commit: r361303 - in head: lib/libc/gen libexec/rtld-elf sys/sys

[John Baldwin]

On 5/21/20 9:56 AM, Konstantin Belousov wrote:
> On Thu, May 21, 2020 at 09:03:44AM -0700, John Baldwin wrote:
>> 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 at 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 at 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?
> 
> It is rather clear, since the dtrace code was pristine, that Solaris
> provides the mapbase.  I do not have Solaris/Illumos box anymore
> (for quite some time), so I cannot check directly.
> 
> My current PoV is that l_addr semantic must be restored, and relocbase
> provided by newly added member.

I am fine with reverting the l_addr semantic.  I'm still not sure how to
resolve the original PR, though perhaps Wine just has to carry a local
patch forever?  GDB will work via the current accident so long as we
never pre-link libraries.  As long as PIE binaries have a starting VA of
0 like our shared libraries then I think GDB will be ok with our PIE
binaries as well.

-- 
John Baldwin