So finally after almost 8 years of dealing with .debug_frame, we are
finally switching to .eh_frame. The reason being stripped kernel
binaries had non-functional unwinder as .debug_frame was gone.
Also, in general .eh_frame seems more common way of doing unwinding.

This also folds a revert of f52e126cc747 ("ARC: unwind: ensure that
.debug_frame is generated (vs. .eh_frame)") to ensure that we start
getting .eh_frame

Reported-by: Daniel Mentz <danielmentz@google.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

This paves way for switching to .eh_frame based unwindiing

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Pull livepatching updates from Jiri Kosina:

 - RO/NX attribute fixes for patch module relocations from Josh
   Poimboeuf.  As part of this effort, module.c has been cleaned up as
   well and livepatching is piggy-backing on this cleanup.  Rusty is OK
   with this whole lot going through livepatching tree.

 - symbol disambiguation support from Chris J Arges.  That series is
   also

        Reviewed-by: Miroslav Benes <mbenes@suse.cz>

   but this came in only after I've alredy pushed out.  Didn't want to
   rebase because of that, hence I am mentioning it here.

 - symbol lookup fix from Miroslav Benes

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: Cleanup module page permission changes
  module: keep percpu symbols in module's symtab
  module: clean up RO/NX handling.
  module: use a structure to encapsulate layout.
  gcov: use within_module() helper.
  module: Use the same logic for setting and unsetting RO/NX
  livepatch: function,sympos scheme in livepatch sysfs directory
  livepatch: add sympos as disambiguator field to klp_reloc
  livepatch: add old_sympos as disambiguator field to klp_func

Instead of seeing empty stack traces, let kernel fail early so dwarf
issues can be fixed sooner

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

The rudimentary CIE.version == 3 handling is already present in code
(for return address register specification)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Blingly ignoring CIE.version != 1 was a bad idea.
It still leaves "desirability" when running perf with callgraphing where libgcc
symbols might show in hotspot.

More importantly, basic CIE.version == 3 support already exists in code:

|
|   retAddrReg = state.version <= 1 ? *ptr++ : get_uleb128(&ptr, end);
|

Next commit with simply add continue-not-bail for CIE.version != 1

This reverts commit 323f41f9e7d0cb5b1d1586aded6682855f1e646d.

ARC dwarf unwinder only supports CIE version == 1
The boot time dwarf sanitizer (part of binary lookup table constructor)
would simply bail if it saw CIE version == 3, rendering unwinder with a
NULL lookup table.

It seems libgcc linked with kernel does have such entries.

With fallback linear search removed, and a NULL binary lookup table,
unwinder fails to generate any stack trace.

So allow graceful ignoring of unsupported CIE entries.

This problem was initially seen in Alexey's setup (and not mine) as he
was using buildroot built toolchain (libgcc) which doesn't get built with
CFLAGS_FOR_TARGET="-gdwarf-2 which is my default

Fixes STAR 9000985048: "kernel unwinder broken with stock tools"

Fixes: 2e22502c080f ARC: dw2 unwind: Remove falllback linear search thru FDE entries
Reported-by Alexey Brodkin <abrodkin@synopsys.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

The fix which removed linear searching of dwarf (because binary lookup
data always exists) missed out on the fact that modules don't get the
binary lookup tables info. This caused unwinding out of modules to stop
working.

So add binary lookup header setup (equivalent of eh_frame_hdr setup) to
modules as well.

While at it, confine the header setup to within unwinder code,
reducing one API exposed out of unwinder code.

Fixes: 2e22502c080f ARC: dw2 unwind: Remove falllback linear search thru FDE entries
Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

Makes it easier to handle init vs core cleanly, though the change is
fairly invasive across random architectures.

It simplifies the rbtree code immediately, however, while keeping the
core data together in the same cachline (now iff the rbtree code is
enabled).

Acked-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Fixes STAR 9000953410: "perf callgraph profiling causing RCU stalls"

| perf record -g -c 15000 -e cycles /sbin/hackbench
|
| INFO: rcu_preempt self-detected stall on CPU
| 1: (1 GPs behind) idle=609/140000000000002/0 softirq=2914/2915 fqs=603
| Task dump for CPU 1:

in-kernel dwarf unwinder has a fast binary lookup and a fallback linear
search (which iterates thru each of ~11K entries) thus takes 2 orders of
magnitude longer (~3 million cycles vs. 2000). Routines written in hand
assembler lack dwarf info (as we don't support assembler CFI pseudo-ops
yet) fail the unwinder binary lookup, hit linear search, failing
nevertheless in the end.

However the linear search is pointless as binary lookup tables are created
from it in first place. It is impossible to have binary lookup fail while
succeed the linear search. It is pure waste of cycles thus removed by
this patch.

This manifested as RCU stalls / NMI watchdog splat when running
hackbench under perf with callgraph profiling. The triggering condition
was perf counter overflowing in routine lacking dwarf info (like memset)
leading to patheic 3 million cycle unwinder slow path and by the time it
returned new interrupts were already pending (Timer, IPI) and taken
rightaway. The original memset didn't make forward progress, system kept
accruing more interrupts and more unwinder delayes in a vicious feedback
loop, ultimately triggering the NMI diagnostic.

Cc: stable@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>