Re: time to workaround libc/13097 in fsf gdb?

[Doug Evans <dje at google dot com>]

Pedro Alves writes:
 > On 09/12/2014 12:54 PM, Jan Kratochvil wrote:
 > > On Thu, 11 Sep 2014 18:37:02 +0200, Pedro Alves wrote:
 > >> Also, we know the address of the vDSO/gate (symfile-mem.c).  Can't
 > >> we use that to match instead of the name?
 > > [...]
 > >> ISTR having seen a patch that does that, but I can't seem to find it.
 > > 
 > > Re: [patch+7.5.1] Work around PR libc/13097 "linux-vdso.so.1" #3
 > > https://sourceware.org/ml/gdb-patches/2012-11/msg00636.html
 > > Message-ID: <20121125181505.GA26194@host2.jankratochvil.net>
 > > 
 > > It is pending/unreviewed/unapproved.
 > 
 > Ah, yeah, I think that was it.
 > 
 > I was more inclined to leave the vdso in the shared library list
 > though, like ldd does, than filtering it out.

I like this too.
No point in hiding it from the user.

 > Like, similar to
 > your gdbarch_solib_file_not_found_is_ok patch, but look at the
 > addresses rather than filenames in the hook.  I'm not sure
 > whether that'd complicate things too much.

I'm not sure either.

It *would* be nice to connect the processing of vdso when seen
by svr4_read_so_list (called during shared library loading)
with add_syscall_page (called as an observer when an inferior
is created).  The same file (vdso) is processed in two disparate places
with no linkage for the human reader between them - a bit confusing.

 > > Also I am not sure it is really still an issue on latest upstream glibc, it is
 > > not an issue on Fedora 21 x86_64 glibc with the reproducer from:
 > > 	https://sourceware.org/bugzilla/show_bug.cgi?id=13097
 > > 
 > > (That is old Fedoras workarounded it in glibc, then some Fedoras exposed the
 > > issue in GDB but now it is not visible - so either Fedoras workaround it again
 > > or just upstream glibc switched/workarounds it also.)

I downloaded glibc 2.20 and tested it with gdb 7.8.
Still an issue.
[I just did a simple build, if there's a configure option
that will fix things I didn't try one.]
I think FSF gdb 7.8[.1?] (the latest) should work with FSF glibc 2.20
(the latest).