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  1. Nov 29, 2016
    • Nicholas Piggin's avatar
      kbuild: kallsyms allow 3-pass generation if symbols size has changed · 7e2b37c9
      Nicholas Piggin authored 
      

kallsyms generation is not foolproof, due to some linkers adding
symbols (e.g., branch trampolines) when a binary size changes.
Have it attempt a 3rd pass automatically if the kallsyms size changes
in the 2nd pass.

This allows powerpc64 allyesconfig to build without adding another
pass when it's not required.

This can be solved other ways by directing the linker not to add labels
on branch stubs, or to move kallsyms near the end of the image. The
former is undesirable for debugging/tracing, and the latter is a more
significant change that requires more testing and review.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichal Marek <mmarek@suse.com>
      7e2b37c9
  3. Oct 11, 2016
  5. Oct 10, 2016
    • Emese Revfy's avatar
      gcc-plugins: Add latent_entropy plugin · 38addce8
      Emese Revfy authored 
      

This adds a new gcc plugin named "latent_entropy". It is designed to
extract as much possible uncertainty from a running system at boot time as
possible, hoping to capitalize on any possible variation in CPU operation
(due to runtime data differences, hardware differences, SMP ordering,
thermal timing variation, cache behavior, etc).

At the very least, this plugin is a much more comprehensive example for
how to manipulate kernel code using the gcc plugin internals.

The need for very-early boot entropy tends to be very architecture or
system design specific, so this plugin is more suited for those sorts
of special cases. The existing kernel RNG already attempts to extract
entropy from reliable runtime variation, but this plugin takes the idea to
a logical extreme by permuting a global variable based on any variation
in code execution (e.g. a different value (and permutation function)
is used to permute the global based on loop count, case statement,
if/then/else branching, etc).

To do this, the plugin starts by inserting a local variable in every
marked function. The plugin then adds logic so that the value of this
variable is modified by randomly chosen operations (add, xor and rol) and
random values (gcc generates separate static values for each location at
compile time and also injects the stack pointer at runtime). The resulting
value depends on the control flow path (e.g., loops and branches taken).

Before the function returns, the plugin mixes this local variable into
the latent_entropy global variable. The value of this global variable
is added to the kernel entropy pool in do_one_initcall() and _do_fork(),
though it does not credit any bytes of entropy to the pool; the contents
of the global are just used to mix the pool.

Additionally, the plugin can pre-initialize arrays with build-time
random contents, so that two different kernel builds running on identical
hardware will not have the same starting values.

Signed-off-by: default avatarEmese Revfy <re.emese@gmail.com>
[kees: expanded commit message and code comments]
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
      38addce8
  7. Oct 08, 2016
  9. Oct 01, 2016
  11. Sep 28, 2016
  13. Sep 23, 2016
  15. Sep 21, 2016
    • Steven Rostedt (Red Hat)'s avatar
      ftrace/scripts: Add helper script to bisect function tracing problem functions · 951dbf50
      Steven Rostedt (Red Hat) authored 
      Every so often, with a special config or a architecture change, running
function or function_graph tracing can cause the machien to hard reboot,
crash, or simply hard lockup. There's some functions in the function graph
tracer that can not be traced otherwise it causes the function tracer to
recurse before the recursion protection mechanisms are in place.

When this occurs, using the dynamic ftrace featuer that allows limiting what
actually gets traced can be used to bisect down to the problem function.
This adds a script that helps with this process in the scripts/tracing
directory, called ftrace-bisect.sh

The set up is to read all the functions that can be traced from
available_filter_functions into a file (full_file). Then run this script
passing it the full_file and a "test_file" and "non_test_file", where the
test_file will be add to set_ftrace_filter. What ftarce_bisect.sh does, is
to copy half of the functions in full_file into the test_file and the other
half into the non_test_file. This way, one can cat the test_file into the
set_ftrace_filter functions and only test the functions that are in that
file. If it works, then we run the process again after copying non_test_file
to full_file and repeating the process. If the system crashed, then the bad
function is in the test_file and after a reboot, the test_file becomes the
new full_file in the next iteration.

When we get down to a single function in the full_file, then
ftrace_bisect.sh will report that as the bad function.

Full documentation of how to use this simple script is within the script
file itself.

Link: http://lkml.kernel.org/r/20160920100716.131d3647@gandalf.local.home



Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      951dbf50
  17. Sep 20, 2016
  19. Sep 19, 2016
  21. Sep 09, 2016
    • Nicholas Piggin's avatar
      kbuild: add arch specific post-link Makefile · fbe6e37d
      Nicholas Piggin authored 
      

Allow architectures to create arch/xxx/Makefile.postlink with targets
for vmlinux, modules.ko, and clean, which will be invoked after final
linking of vmlinux and modules.

powerpc will use this to check vmlinux linker relocations for sanity,
and may use it to fix up alternate instruction patch branch addresses.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichal Marek <mmarek@suse.com>
      fbe6e37d
    • Stephen Rothwell's avatar
      kbuild: allow architectures to use thin archives instead of ld -r · a5967db9
      Stephen Rothwell authored 
      

ld -r is an incremental link used to create built-in.o files in build
subdirectories. It produces relocatable object files containing all
its input files, and these are are then pulled together and relocated
in the final link. Aside from the bloat, this constrains the final
link relocations, which has bitten large powerpc builds with
unresolvable relocations in the final link.

Alan Modra has recommended the kernel use thin archives for linking.
This is an alternative and means that the linker has more information
available to it when it links the kernel.

This patch enables a config option architectures can select, which
causes all built-in.o files to be built as thin archives. built-in.o
files in subdirectories do not get symbol table or index attached,
which improves speed and size. The final link pass creates a
built-in.o archive in the root output directory which includes the
symbol table and index. The linker then uses takes this file to link.

The --whole-archive linker option is required, because the linker now
has visibility to every individual object file, and it will otherwise
just completely avoid including those without external references
(consider a file with EXPORT_SYMBOL or initcall or hardware exceptions
as its only entry points). The traditional built works "by luck" as
built-in.o files are large enough that they're going to get external
references. However this optimisation is unpredictable for the kernel
(due to above external references), ineffective at culling unused, and
costly because the .o files have to be searched for references.
Superior alternatives for link-time culling should be used instead.

Build characteristics for inclink vs thinarc, on a small powerpc64le
pseries VM with a modest .config:

                                  inclink       thinarc
sizes
vmlinux                        15 618 680    15 625 028
sum of all built-in.o          56 091 808     1 054 334
sum excluding root built-in.o                   151 430

find -name built-in.o | xargs rm ; time make vmlinux
real                              22.772s       21.143s
user                              13.280s       13.430s
sys                                4.310s        2.750s

- Final kernel pulled in only about 6K more, which shows how
  ineffective the object file culling is.
- Build performance looks improved due to less pagecache activity.
  On IO constrained systems it could be a bigger win.
- Build size saving is significant.

Side note, the toochain understands archives, so there's some tricks,
$ ar t built-in.o          # list all files you linked with
$ size built-in.o          # and their sizes
$ objdump -d built-in.o    # disassembly (unrelocated) with filenames

Implementation by sfr, minor tweaks by npiggin.

Signed-off-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichal Marek <mmarek@suse.com>
      a5967db9
  23. Sep 06, 2016
  25. Sep 02, 2016
  27. Sep 01, 2016
    • Mauro Carvalho Chehab's avatar
      docs-rst: kernel-doc: fix typedef output in RST format · 82801d06
      Mauro Carvalho Chehab authored 
      

When using a typedef function like this one:
	typedef bool v4l2_check_dv_timings_fnc (const struct v4l2_dv_timings * t, void * handle);

The Sphinx C domain expects it to create a c:type: reference,
as that's the way it creates the type references when parsing
a c:function:: declaration.

So, a declaration like:

	.. c:function:: bool v4l2_valid_dv_timings (const struct v4l2_dv_timings * t, const struct v4l2_dv_timings_cap * cap, v4l2_check_dv_timings_fnc fnc, void * fnc_handle)

Will create a cross reference for :c:type:`v4l2_check_dv_timings_fnc`.

So, when outputting such typedefs in RST format, we need to handle
this special case, as otherwise it will produce those warnings:

	./include/media/v4l2-dv-timings.h:43: WARNING: c:type reference target not found: v4l2_check_dv_timings_fnc
	./include/media/v4l2-dv-timings.h:60: WARNING: c:type reference target not found: v4l2_check_dv_timings_fnc
	./include/media/v4l2-dv-timings.h:81: WARNING: c:type reference target not found: v4l2_check_dv_timings_fnc

So, change the kernel-doc script to produce a RST output for the
above typedef as:
	.. c:type:: v4l2_check_dv_timings_fnc

	   **Typedef**: timings check callback

	**Syntax**

	  ``bool v4l2_check_dv_timings_fnc (const struct v4l2_dv_timings * t, void * handle);``

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
      82801d06
    • Mauro Carvalho Chehab's avatar
      docs-rst: improve typedef parser · d37c43ce
      Mauro Carvalho Chehab authored 
      

Improve the parser to handle typedefs like:

	typedef bool v4l2_check_dv_timings_fnc(const struct v4l2_dv_timings *t, void *handle);

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
      d37c43ce
  29. Aug 31, 2016
  31. Aug 28, 2016