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 <k...@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....@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 should be an absolute address, since dtrace appears to assume that an
ELF header is mapped at l_addr.

Here, "addr" is the value of l_addr for the RTLD_SELF linkmap:
https://github.com/joyent/illumos-joyent/blob/master/usr/src/lib/libdtrace/common/dlink_common.c#L124
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