[Crash-utility] [PATCH][v2] Remove __exception_text_start and __exception_text_end for ARM64

[Dave Anderson]

----- Original Message -----
> > Hi Prabhakar,
> >
> > On Mon, Dec 30, 2019 at 9:55 AM Prabhakar Kushwaha
> > <prabhakar.pkin at gmail.com> wrote:
> >>
> >> Dear Bhupesh,
> >>
> >> On Tue, Dec 24, 2019 at 9:39 AM Prabhakar Kushwaha
> >> <prabhakar.pkin at gmail.com> wrote:
> >> >
> >> > On Tue, Dec 24, 2019 at 1:09 AM Bhupesh Sharma <bhsharma at redhat.com>
> >> wrote:
> >> > >
> >> > > On Mon, Dec 23, 2019 at 7:49 PM Prabhakar Kushwaha
> >> > > <prabhakar.pkin at gmail.com> wrote:
> >> > > >
> >> > > > On Mon, Dec 23, 2019 at 7:32 PM Dave Anderson
> >> <anderson at redhat.com> wrote:
> >> > > > >
> >> > > > >
> >> > > > >
> >> > > > > ----- Original Message -----
> >> > > > > > __exception_text_start and __exception_text_end is used to
> >> group functions
> >> > > > > > and place according to linker script in such a way to achieve
> >> > > > > > kprobe blacklist. Linux commit b6e43c0e3129 ("arm64: remove
> >> __exception
> >> > > > > > annotations") has removed __exception_text_start and
> >> > > > > > __exception_text_end and uses NOKPROBE_SYMBOL() for blacklist
> >> kprobes.
> >> > > > > >
> >> > > > > > So removing references of __exception_text_start and
> >> __exception_text_end
> >> > > > > > for ARM64.
> >> > > > >
> >> > > > > NAK for a couple of reasons...
> >> > > > >
> >> > > > > First, they cannot be removed for backward-compatibility
> >> purposes, and secondly
> >> > > > > an alternative method is required for arm64_back_trace_cmd() for
> >> handling
> >> > > > > exception frames.
> >> > > > >
> >> > > >
> >> > > > We are getting following error with crash tool with latest kernel.
> >> > > > crash: cannot resolve "__exception_text_start" error
> >> > > >
> >> > > > it is because of Linux commit b6e43c0e3129 which removes
> >> > > > __exception_text_start and __exception_text_end.
> >> > > > We need to find alternate way of fixing it.
> >> > >
> >> > > I cannot seem to remember reproducing this issue with crash with
> >> > > latest kernel on my arm64 boards.
> >> > > Can you be more specific on the exact kernel version and the crash
> >> > > command you used, just to be sure we are able to reproduce the same?
> >> > >
> >> >
> >> > We are seeing this issue on Thuder X platform (arm64).
> >> >
> >> > Please find details of commit id.
> >> > A) crash tool: https://github.com/crash-utility/crash.git
> >> > commit:  af7f78dc501b8acf7fee3f924f69e93513d0a74b (Fix for the "log
> >> -a" option.)
> >> >
> >> > B) Linux:
> >> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >> > commit:  46cf053efec6a3a5f343fead837777efe8252a46 (Linux 5.5-rc3)
> >> >
> >> > C) Kexec:
> >> https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
> >> > commit: bd077966e2b9041c24df5b689e67670f02be7b0d (kexec-tools: Fix
> >> > conversion overflow when compiling on 32-bit platforms)
> >> >
> >> >
> >> > Logs
> >> > root at ubuntu$ ./crash /proc/vmcore /usr/src/tovards/linux/vmlinux
> >> >
> >> > crash 7.2.7++
> >> > Copyright (C) 2002-2019  Red Hat, Inc.
> >> > Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation
> >> > Copyright (C) 1999-2006  Hewlett-Packard Co
> >> > Copyright (C) 2005, 2006, 2011, 2012  Fujitsu Limited
> >> > Copyright (C) 2006, 2007  VA Linux Systems Japan K.K.
> >> > Copyright (C) 2005, 2011  NEC Corporation
> >> > Copyright (C) 1999, 2002, 2007  Silicon Graphics, Inc.
> >> > Copyright (C) 1999, 2000, 2001, 2002  Mission Critical Linux, Inc.
> >> > This program is free software, covered by the GNU General Public
> >> License,
> >> > and you are welcome to change it and/or distribute copies of it under
> >> > certain conditions.  Enter "help copying" to see the conditions.
> >> > This program has absolutely no warranty.  Enter "help warranty" for
> >> details.
> >> >
> >> > vmcoreinfo : vabits_actual: 48
> >> > GNU gdb (GDB) 7.6
> >> > Copyright (C) 2013 Free Software Foundation, Inc.
> >> > License GPLv3+: GNU GPL version 3 or later
> >> <http://gnu.org/licenses/gpl.html>
> >> > This is free software: you are free to change and redistribute it.
> >> > There is NO WARRANTY, to the extent permitted by law.  Type "show
> >> copying"
> >> > and "show warranty" for details.
> >> > This GDB was configured as "aarch64-unknown-linux-gnu".
> >> > For bug reporting instructions, please see:
> >> > <http://www.gnu.org/software/gdb/bugs/>...
> >> >
> >> > crash: cannot resolve "__exception_text_start"
> >> >
> >>
> >> i hope you got sometime to reproduce this issue.
> >> It can also be seen on Linux 5.5-rc4 tag
> >> (fd6988496e79a6a4bdb514a4655d2920209eb85d).
> >>
> >> crash-util  commit 5e975dd8c817ea6aea35e1e15b83c378aee9c136 (HEAD ->
> >> master, origin/master, origin/HEAD)
> >
> > I was able to reproduce the issue with latest Linus's tree. I am
> > working on a patch (as per Dave's suggestion) to fix backward
> > compatibility as well as 'arm64_back_trace_cmd()' (bt command support)
> > and will post it out soon (I am hoping to post out a version after the
> > new year break).
> >
> > Thanks  and a Happy New Year,
> > Bhupesh
> >
> 
> Thanks Bhupesh, I'm also out until next week.
> 
> And yeah, for 5.5 and later kernels it looks like
> arm64_in_exception_text() will have to check the incoming
> address's symbol name against the set of exception handler
> symbol names.  The older kernels can still utilize the handy
> text range between __exception_text_start/__exception_text_end.
> 
> Kind of a pain, but I don't know what the alternative would be.
> 
> Dave

Hi Bhupesh,

Here's what I'm thinking...  (attached patch)

Thanks,
  Dave
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