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Re: [PATCH] Improve corefile generation by using /proc/PID/coredump_filter (PR corefile/16902)
- From: Oleg Nesterov <oleg at redhat dot com>
- To: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- Cc: Sergio Durigan Junior <sergiodj at redhat dot com>, GDB Patches <gdb-patches at sourceware dot org>, Pedro Alves <palves at redhat dot com>
- Date: Thu, 12 Mar 2015 16:00:24 +0100
- Subject: Re: [PATCH] Improve corefile generation by using /proc/PID/coredump_filter (PR corefile/16902)
- Authentication-results: sourceware.org; auth=none
- References: <878ufc9kau dot fsf at redhat dot com> <20150305154827 dot GA9441 at host1 dot jankratochvil dot net> <87zj7r5fpz dot fsf at redhat dot com> <20150305205744 dot GA13165 at host1 dot jankratochvil dot net> <20150311200052 dot GA22654 at redhat dot com>
See another email I sent, perhaps this needs more discussion...
On 03/11, Oleg Nesterov wrote:
> On 03/05, Jan Kratochvil wrote:
> > On Thu, 05 Mar 2015 21:52:56 +0100, Sergio Durigan Junior wrote:
> > > On Thursday, March 05 2015, Jan Kratochvil wrote:
> > > > On Thu, 05 Mar 2015 04:48:09 +0100, Sergio Durigan Junior wrote:
> > > > Currently it also tries to dump [vvar] (by default rules) but that is
> > > > unreadable for some reason, causing:
> > > > warning: Memory read failed for corefile section, 8192 bytes at 0x7ffff6ceb000.
> > > > ^^^^^^^^^^^^^^
> > > > Saved corefile /tmp/1j
> > > > (gdb) _
> > > > # grep 7ffff6ceb000 /proc/$p/maps
> > > > 7ffff6ceb000-7ffff6ced000 r--p 00000000 00:00 0 [vvar]
> > > > ^^^^^^^^^^^^ ^^^^
> > > >
> > > > I do not know what [vvar] is good for and why it cannot be read.
> Probably gdb doesn't need to dump this vma, but see below.
Probably yes. Note that it has VM_DONTDUMP ("dd" in "VmFlags:" field).
However. If (for any reason) you decide to dump this region, gdb can
look into /proc/self/maps, find its own "vvar" mapping, and simply read
this memory. Unlike "vdso", "vvar" has the same content for every process.
(just in case, "vdso" is the same too but it is MAYWRITE, so it can have
anonymous pages. Say, breakpoints installed by gdb).