Documentation: x86: convert orc-unwinder.txt to reST

This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/x86/index.rst

@@ -14,6 +14,7 @@ x86-specific Documentation
    kernel-stacks
    entry_64
    earlyprintk
+   orc-unwinder
    zero-page
    tlb
    mtrr

Documentation/x86/orc-unwinder.txt → Documentation/x86/orc-unwinder.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+============
 ORC unwinder
 ============
 
 Overview
---------
+========
 
 The kernel CONFIG_UNWINDER_ORC option enables the ORC unwinder, which is
 similar in concept to a DWARF unwinder.  The difference is that the
@@ -23,12 +26,12 @@ correlate instruction addresses with their stack states at run time.
 
 
 ORC vs frame pointers
----------------------
+=====================
 
 With frame pointers enabled, GCC adds instrumentation code to every
 function in the kernel.  The kernel's .text size increases by about
 3.2%, resulting in a broad kernel-wide slowdown.  Measurements by Mel
-Gorman [1] have shown a slowdown of 5-10% for some workloads.
+Gorman [1]_ have shown a slowdown of 5-10% for some workloads.
 
 In contrast, the ORC unwinder has no effect on text size or runtime
 performance, because the debuginfo is out of band.  So if you disable
@@ -55,7 +58,7 @@ depending on the kernel config.
 
 
 ORC vs DWARF
-------------
+============
 
 ORC debuginfo's advantage over DWARF itself is that it's much simpler.
 It gets rid of the complex DWARF CFI state machine and also gets rid of
@@ -65,7 +68,7 @@ mission critical oops code.
 
 The simpler debuginfo format also enables the unwinder to be much faster
 than DWARF, which is important for perf and lockdep.  In a basic
-performance test by Jiri Slaby [2], the ORC unwinder was about 20x
+performance test by Jiri Slaby [2]_, the ORC unwinder was about 20x
 faster than an out-of-tree DWARF unwinder.  (Note: That measurement was
 taken before some performance tweaks were added, which doubled
 performance, so the speedup over DWARF may be closer to 40x.)
@@ -85,7 +88,7 @@ still be able to control the format, e.g. no complex state machines.
 
 
 ORC unwind table generation
----------------------------
+===========================
 
 The ORC data is generated by objtool.  With the existing compile-time
 stack metadata validation feature, objtool already follows all code
@@ -133,7 +136,7 @@ objtool follows GCC code quite well.
 
 
 Unwinder implementation details
--------------------------------
+===============================
 
 Objtool generates the ORC data by integrating with the compile-time
 stack metadata validation feature, which is described in detail in
@@ -154,7 +157,7 @@ subset of the table needs to be searched.
 
 
 Etymology
----------
+=========
 
 Orcs, fearsome creatures of medieval folklore, are the Dwarves' natural
 enemies.  Similarly, the ORC unwinder was created in opposition to the
@@ -162,7 +165,7 @@ complexity and slowness of DWARF.
 
 "Although Orcs rarely consider multiple solutions to a problem, they do
 excel at getting things done because they are creatures of action, not
-thought." [3]  Similarly, unlike the esoteric DWARF unwinder, the
+thought." [3]_  Similarly, unlike the esoteric DWARF unwinder, the
 veracious ORC unwinder wastes no time or siloconic effort decoding
 variable-length zero-extended unsigned-integer byte-coded
 state-machine-based debug information entries.
@@ -174,6 +177,6 @@ brutal, unyielding efficiency.
 ORC stands for Oops Rewind Capability.
 
 
-[1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@suse.de
-[2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz
-[3] http://dustin.wikidot.com/half-orcs-and-orcs
+.. [1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@suse.de
+.. [2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz
+.. [3] http://dustin.wikidot.com/half-orcs-and-orcs