objtool/LoongArch: Enable orc to be built

Implement arch-specific init_orc_entry(), write_orc_entry(), reg_name(),
orc_type_name(), print_reg() and orc_print_dump(), then set BUILD_ORC as
y to build the orc related files.

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

objtool: Fix HOSTCC flag usage

HOSTCC is always wanted when building objtool. Setting CC to HOSTCC
happens after tools/scripts/Makefile.include is included, meaning
flags (like CFLAGS) are set assuming say CC is gcc, but then it can be
later set to HOSTCC which may be clang. tools/scripts/Makefile.include
is needed for host set up and common macros in objtool's
Makefile. Rather than override the CC variable to HOSTCC, just pass CC
as HOSTCC to the sub-makes of Makefile.build, the libsubcmd builds and
also to the linkage step.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230126190606.40739-4-irogers@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

objtool: Properly support make V=1

The Q variable was being used but never correctly set up. Add the
setting up and use in place of @.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230126190606.40739-3-irogers@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

objtool: Install libsubcmd in build

Including from tools/lib can create inadvertent dependencies. Install
libsubcmd in the objtool build and then include the headers from
there.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20230126190606.40739-2-irogers@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

kbuild: Allow kernel installation packaging to override pkg-config

Add HOSTPKG_CONFIG to allow tooling that builds the kernel to override
what pkg-config and parameters are used.

Signed-off-by: Chun-Tse Shao <ctshao@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

objtool: Remove libsubcmd.a when make clean

The file libsubcmd.a still exists after make clean, remove it.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/1652258270-6278-3-git-send-email-yangtiezhu@loongson.cn

objtool: Remove inat-tables.c when make clean

When build objtool on x86, the generated file inat-tables.c is in
arch/x86/lib instead of arch/x86, use the correct dir to remove it
when make clean.

$ cd tools/objtool
$ make
[...]
GEN arch/x86/lib/inat-tables.c
[...]

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/1652258270-6278-2-git-send-email-yangtiezhu@loongson.cn

objtool: Ditch subcommands

Objtool has a fairly singular focus. It runs on object files and does
validations and transformations which can be combined in various ways.
The subcommand model has never been a good fit, making it awkward to
combine and remove options.

Remove the "check" and "orc" subcommands in favor of a more traditional
cmdline option model. This makes it much more flexible to use, and
easier to port individual features to other arches.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/5c61ebf805e90aefc5fa62bc63468ffae53b9df6.1650300597.git.jpoimboe@redhat.com

kbuild: replace $(if A,A,B) with $(or A,B)

$(or ...) is available since GNU Make 3.81, and useful to shorten the
code in some places.

Covert as follows:

$(if A,A,B) --> $(or A,B)

This patch also converts:

$(if A, A, B) --> $(or A, B)

Strictly speaking, the latter is not an equivalent conversion because
GNU Make keeps spaces after commas; if A is not empty, $(if A, A, B)
expands to " A", while $(or A, B) expands to "A".

Anyway, preceding spaces are not significant in the code hunks I touched.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

objtool: Refactor ORC section generation

Decouple ORC entries from instructions. This simplifies the
control/data flow, and is going to make it easier to support alternative
instructions which change the stack layout.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

objtool: Rework header include paths

Currently objtool headers are being included either by their base name
or included via ../ from a parent directory. In case of a base name usage:

#include "warn.h"
#include "arch_elf.h"

it does not make it apparent from which directory the file comes from.
To make it slightly better, and actually to avoid name clashes some arch
specific files have "arch_" suffix. And files from an arch folder have
to revert to including via ../ e.g:
#include "../../elf.h"

With additional architectures support and the code base growth there is
a need for clearer headers naming scheme for multiple reasons:
1. to make it instantly obvious where these files come from (objtool
itself / objtool arch|generic folders / some other external files),
2. to avoid name clashes of objtool arch specific headers, potential
obtool arch generic headers and the system header files (there is
/usr/include/elf.h already),
3. to avoid ../ includes and improve code readability.
4. to give a warm fuzzy feeling to developers who are mostly kernel
developers and are accustomed to linux kernel headers arranging
scheme.

Doesn't this make it instantly obvious where are these files come from?

#include <objtool/warn.h>
#include <arch/elf.h>

And doesn't it look nicer to avoid ugly ../ includes? Which also
guarantees this is elf.h from the objtool and not /usr/include/elf.h.

#include <objtool/elf.h>

This patch defines and implements new objtool headers arranging
scheme. Which is:
- all generic headers go to include/objtool (similar to include/linux)
- all arch headers go to arch/$(SRCARCH)/include/arch (to get arch
prefix). This is similar to linux arch specific "asm/*" headers but we
are not abusing "asm" name and calling it what it is. This also helps
to prevent name clashes (arch is not used in system headers or kernel
exports).

To bring objtool to this state the following things are done:
1. current top level tools/objtool/ headers are moved into
include/objtool/ subdirectory,
2. arch specific headers, currently only arch/x86/include/ are moved into
arch/x86/include/arch/ and were stripped of "arch_" suffix,
3. new -I$(srctree)/tools/objtool/include include path to make
includes like <objtool/warn.h> possible,
4. rewriting file includes,
5. make git not to ignore include/objtool/ subdirectory.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

tools: Factor HOSTCC, HOSTLD, HOSTAR definitions

Several Makefiles in tools/ need to define the host toolchain variables.
Move their definition to tools/scripts/Makefile.include

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/bpf/20201110164310.2600671-2-jean-philippe@linaro.org

objtool: Allow nested externs to enable BUILD_BUG()

Currently BUILD_BUG() macro is expanded to smth like the following:
do {
extern void __compiletime_assert_0(void)
__attribute__((error("BUILD_BUG failed")));
if (!(!(1)))
__compiletime_assert_0();
} while (0);

If used in a function body this obviously would produce build errors
with -Wnested-externs and -Werror.

Build objtool with -Wno-nested-externs to enable BUILD_BUG() usage.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

objtool: Define 'struct orc_entry' only when needed

Implementation of ORC requires some definitions that are currently
provided by the target architecture headers. Do not depend on these
definitions when the orc subcommand is not implemented.

This avoid requiring arches with no orc implementation to provide dummy
orc definitions.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

objtool: Enable compilation of objtool for all architectures

Objtool currently only compiles for x86 architectures. This is
fine as it presently does not support tooling for other
architectures. However, we would like to be able to convert other
kernel tools to run as objtool sub commands because they too
process ELF object files. This will allow us to convert tools
such as recordmcount to use objtool's ELF code.

Since much of recordmcount's ELF code is copy-paste code to/from
a variety of other kernel tools (look at modpost for example) this
means that if we can convert recordmcount we can convert more.

We define weak definitions for subcommand entry functions and other weak
definitions for shared functions critical to building existing
subcommands. These return 127 when the command is missing which signify
tools that do not exist on all architectures. In this case the "check"
and "orc" tools do not exist on all architectures so we only add them
for x86. Future changes adding support for "check", to arm64 for
example, can then modify the SUBCMD_CHECK variable when building for
arm64.

Objtool is not currently wired in to KConfig to be built for other
architectures because it's not needed for those architectures and
there are no commands it supports other than those for x86. As more
command support is enabled on various architectures the necessary
KConfig changes can be made (e.g. adding "STACK_VALIDATION") to
trigger building objtool.

[ jpoimboe: remove aliases, add __weak macro, add error messages ]

Cc: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

objtool: Split out arch-specific CFI definitions

Some CFI definitions used by generic objtool code have no reason to vary
from one architecture to another. Keep those definitions in generic
code and move the arch-specific ones to a new arch-specific header.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Always do header sync check

Currently, the check of tools files against kernel equivalent is only
done after every object file has been built. This means one might fix
build issues against outdated headers without seeing a warning about
this.

Check headers before any object is built. Also, make it part of a
FORCE'd recipe so every attempt to build objtool will report the
outdated headers (if any).

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kbuild: support LLVM=1 to switch the default tools to Clang/LLVM

As Documentation/kbuild/llvm.rst implies, building the kernel with a
full set of LLVM tools gets very verbose and unwieldy.

Provide a single switch LLVM=1 to use Clang and LLVM tools instead
of GCC and Binutils. You can pass it from the command line or as an
environment variable.

Please note LLVM=1 does not turn on the integrated assembler. You need
to pass LLVM_IAS=1 to use it. When the upstream kernel is ready for the
integrated assembler, I think we can make it default.

We discussed what we need, and we agreed to go with a simple boolean
flag that switches both target and host tools:

https://lkml.org/lkml/2020/3/28/494
https://lkml.org/lkml/2020/4/3/43

Some items discussed, but not adopted:

- LLVM_DIR

When multiple versions of LLVM are installed, I just thought supporting
LLVM_DIR=/path/to/my/llvm/bin/ might be useful.

CC = $(LLVM_DIR)clang
LD = $(LLVM_DIR)ld.lld
...

However, we can handle this by modifying PATH. So, we decided to not do
this.

- LLVM_SUFFIX

Some distributions (e.g. Debian) package specific versions of LLVM with
naming conventions that use the version as a suffix.

CC = clang$(LLVM_SUFFIX)
LD = ld.lld(LLVM_SUFFIX)
...

will allow a user to pass LLVM_SUFFIX=-11 to use clang-11 etc.,
but the suffixed versions in /usr/bin/ are symlinks to binaries in
/usr/lib/llvm-#/bin/, so this can also be handled by PATH.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com> # build
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

objtool: Fix ARCH=x86_64 build error

Building objtool with ARCH=x86_64 fails with:

$make ARCH=x86_64 -C tools/objtool
...
CC arch/x86/decode.o
arch/x86/decode.c:10:22: fatal error: asm/insn.h: No such file or directory
#include <asm/insn.h>
^
compilation terminated.
mv: cannot stat ‘arch/x86/.decode.o.tmp’: No such file or directory
make[2]: *** [arch/x86/decode.o] Error 1
...

The root cause is that the command-line variable 'ARCH' cannot be
overridden. It can be replaced by 'SRCARCH', which is defined in
'tools/scripts/Makefile.arch'.

Signed-off-by: Shile Zhang <shile.zhang@linux.alibaba.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Link: https://lore.kernel.org/r/d5d11370ae116df6c653493acd300ec3d7f5e925.1579543924.git.jpoimboe@redhat.com

objtool: Clobber user CFLAGS variable

If the build user has the CFLAGS variable set in their environment,
objtool blindly appends to it, which can cause unexpected behavior.

Clobber CFLAGS to ensure consistent objtool compilation behavior.

Reported-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Tested-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/83a276df209962e6058fcb6c615eef9d401c21bc.1567121311.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Move x86 insn decoder to a common location

The kernel tree has three identical copies of the x86 instruction
decoder. Two of them are in the tools subdir.

The tools subdir is supposed to be completely standalone and separate
from the kernel. So having at least one copy of the kernel decoder in
the tools subdir is unavoidable. However, we don't need *two* of them.

Move objtool's copy of the decoder to a shared location, so that perf
will also be able to use it.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: x86@kernel.org
Link: http://lore.kernel.org/lkml/55b486b88f6bcd0c9a2a04b34f964860c8390ca8.1567118001.git.jpoimboe@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Allow AR to be overridden with HOSTAR

Currently, this Makefile hardcodes GNU ar, meaning that if it is not
available, there is no way to supply a different one and the build will
fail.

$ make AR=llvm-ar CC=clang LD=ld.lld HOSTAR=llvm-ar HOSTCC=clang \
HOSTLD=ld.lld HOSTLDFLAGS=-fuse-ld=lld defconfig modules_prepare
...
AR /out/tools/objtool/libsubcmd.a
/bin/sh: 1: ar: not found
...

Follow the logic of HOST{CC,LD} and allow the user to specify a
different ar tool via HOSTAR (which is used elsewhere in other
tools/ Makefiles).

Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Cc: <stable@vger.kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/80822a9353926c38fd7a152991c6292491a9d0e8.1558028966.git.jpoimboe@redhat.com
Link: https://github.com/ClangBuiltLinux/linux/issues/481
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Query pkg-config for libelf location

If it is not in the default location, compilation fails at several points.

Signed-off-by: Rolf Eike Beer <eb@emlix.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/91a25e992566a7968fedc89ec80e7f4c83ad0548.1553622500.git.jpoimboe@redhat.com

kbuild: Rename HOSTLDFLAGS to KBUILD_HOSTLDFLAGS

In preparation for enabling command line LDFLAGS, re-name HOSTLDFLAGS
to KBUILD_HOSTLDFLAGS as the internal use only flags. This should not
have any visible effects.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

kbuild: Rename HOSTCFLAGS to KBUILD_HOSTCFLAGS

In preparation for enabling command line CFLAGS, re-name HOSTCFLAGS to
KBUILD_HOSTCFLAGS as the internal use only flags. This should not have
any visible effects.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

objtool: Support HOSTCFLAGS and HOSTLDFLAGS

It may be useful to compile host programs with different flags (e.g.
hardening). Ensure that objtool picks up the appropriate flags.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kbuild@vger.kernel.org
Link: http://lkml.kernel.org/r/05a360681176f1423cb2fde8faae3a0a0261afc5.1523560825.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Kbuild: fix # escaping in .cmd files for future Make

I tried building using a freshly built Make (4.2.1-69-g8a731d1), but
already the objtool build broke with

orc_dump.c: In function ‘orc_dump’:
orc_dump.c:106:2: error: ‘elf_getshnum’ is deprecated [-Werror=deprecated-declarations]
if (elf_getshdrnum(elf, &nr_sections)) {

Turns out that with that new Make, the backslash was not removed, so cpp
didn't see a #include directive, grep found nothing, and
-DLIBELF_USE_DEPRECATED was wrongly put in CFLAGS.

Now, that new Make behaviour is documented in their NEWS file:

* WARNING: Backward-incompatibility!
Number signs (#) appearing inside a macro reference or function invocation
no longer introduce comments and should not be escaped with backslashes:
thus a call such as:
foo := $(shell echo '#')
is legal. Previously the number sign needed to be escaped, for example:
foo := $(shell echo '\#')
Now this latter will resolve to "\#". If you want to write makefiles
portable to both versions, assign the number sign to a variable:
C := \#
foo := $(shell echo '$C')
This was claimed to be fixed in 3.81, but wasn't, for some reason.
To detect this change search for 'nocomment' in the .FEATURES variable.

This also fixes up the two make-cmd instances to replace # with $(pound)
rather than with \#. There might very well be other places that need
similar fixup in preparation for whatever future Make release contains
the above change, but at least this builds an x86_64 defconfig with the
new make.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=197847
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

tools/objtool/Makefile: don't assume sync-check.sh is executable

patch(1) loses the x bit. So if a user follows our patching
instructions in Documentation/admin-guide/README.rst, their kernel will
not compile.

Fixes: 3bd51c5a371de ("objtool: Move kernel headers/code sync check to a script")
Reported-by: Nicolas Bock <nicolasbock@gentoo.org>
Reported-by Joakim Tjernlund <Joakim.Tjernlund@infinera.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

objtool: Fix 64-bit build on 32-bit host

The new ORC unwinder breaks the build of a 64-bit kernel on a 32-bit
host. Building the kernel on a i386 or x32 host fails with:

orc_dump.c: In function 'orc_dump':
orc_dump.c:105:26: error: passing argument 2 of 'elf_getshdrnum' from incompatible pointer type [-Werror=incompatible-pointer-types]
if (elf_getshdrnum(elf, &nr_sections)) {
^
In file included from /usr/local/include/gelf.h:32:0,
from elf.h:22,
from warn.h:26,
from orc_dump.c:20:
/usr/local/include/libelf.h:304:12: note: expected 'size_t * {aka unsigned int *}' but argument is of type 'long unsigned int *'
extern int elf_getshdrnum (Elf *__elf, size_t *__dst);
^~~~~~~~~~~~~~
orc_dump.c:190:17: error: format '%lx' expects argument of type 'long unsigned int', but argument 3 has type 'Elf64_Sxword {aka long long int}' [-Werror=format=]
printf("%s+%lx:", name, rela.r_addend);
~~^ ~~~~~~~~~~~~~
%llx

Fix the build failure.

Another problem is that if the user specifies HOSTCC or HOSTLD
variables, they are ignored in the objtool makefile. Change the
Makefile to respect these variables.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sven Joachim <svenjoac@gmx.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 627fce14809b ("objtool: Add ORC unwind table generation")
Link: http://lkml.kernel.org/r/19f0e64d8e07e30a7b307cd010eb780c404fe08d.1512252895.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Fix cross-build

Stephen Rothwell reported this cross-compilation build failure:

| In file included from orc_dump.c:19:0:
| orc.h:21:10: fatal error: asm/orc_types.h: No such file or directory
| ...

Caused by:

6a77cff819ae ("objtool: Move synced files to their original relative locations")

Use the proper arch header files location, not the host-arch location.

Bisected-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux-Next Mailing List <linux-next@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171108030152.bd76eahiwjwjt3kp@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Move kernel headers/code sync check to a script

Replace the nasty diff checks in the objtool Makefile with a clean bash
script, and make the warnings more specific.

Heavily inspired by tools/perf/check-headers.sh.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/ab015f15ccd8c0c6008493c3c6ee3d495eaf2927.1509974346.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Move synced files to their original relative locations

This will enable more straightforward comparisons, and it also makes the
files 100% identical.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/407b2aaa317741f48fcf821592c0e96ab3be1890.1509974346.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.

For non */uapi/* files that summary was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139

and resulted in the first patch in this series.

If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930

and resulted in the second patch in this series.

- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:

SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1

and that resulted in the third patch in this series.

- when the two scanners agreed on the detected license(s), that became
the concluded license(s).

- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.

- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).

- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.

- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct

This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

objtool: Disable GCC '-Wpacked' warnings

Objtool is failing to build with GCC 4.4.7 due to the following
warnings:

cc1: warnings being treated as errors
In file included from orc.h:21,
from orc_gen.c:21:
orc_types.h:86: error: packed attribute is unnecessary for ‘sp_offset’
orc_types.h:87: error: packed attribute is unnecessary for ‘bp_offset’
orc_types.h:88: error: packed attribute is unnecessary for ‘sp_reg’

I suspect those warnings are a GCC bug. But -Wpacked isn't very useful
anyway, so just disable it.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 627fce14809b ("objtool: Add ORC unwind table generation")
Link: http://lkml.kernel.org/r/76d85d7b5a87566465095c500bce222ff5d7b146.1501188854.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool, x86: Add facility for asm code to provide unwind hints

Some asm (and inline asm) code does special things to the stack which
objtool can't understand. (Nor can GCC or GNU assembler, for that
matter.) In such cases we need a facility for the code to provide
annotations, so the unwinder can unwind through it.

This provides such a facility, in the form of unwind hints. They're
similar to the GNU assembler .cfi* directives, but they give more
information, and are needed in far fewer places, because objtool can
fill in the blanks by following branches and adjusting the stack pointer
for pushes and pops.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/0f5f3c9104fca559ff4088bece1d14ae3bca52d5.1499786555.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Implement stack validation 2.0

This is a major rewrite of objtool. Instead of only tracking frame
pointer changes, it now tracks all stack-related operations, including
all register saves/restores.

In addition to making stack validation more robust, this also paves the
way for undwarf generation.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/678bd94c0566c6129bcc376cddb259c4c5633004.1498659915.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

make use of make variable CURDIR instead of calling pwd

make already provides the current working directory in a variable, so make
use of it instead of forking a shell. Also replace usage of PWD by
CURDIR. PWD is provided by most shells, but not all, so this makes the
build system more robust.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Michal Marek <mmarek@suse.com>

objtool: Un-capitalize "Warning" for out-of-sync instruction decoder

Change "Warning" to "warning" to make it look more like a GCC warning.
Hopefully that will be enough to help the 0-day bot or other automated
tools catch this warning earlier before it ends up in Linus's tree.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b1669f391a5db91040427fd9f8e1e79db18f9709.1469751119.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools build: Fix objtool build with ARCH=x86_64

The objtool build fails in a cross-compiled environment on a non-x86
host with "ARCH=x86_64":

tools/objtool/objtool-in.o: In function `decode_instructions':
tools/objtool/builtin-check.c:276: undefined reference to `arch_decode_instruction'

We could override the ARCH environment variable and change it back to
x86, similar to what the objtool Makefile was doing before; but it's
tricky to override environment variables consistently.

Instead, take a similar approach used by the Linux top-level Makefile
and introduce a SRCARCH Makefile variable which evaluates to "x86" when
ARCH is either "x86_64" or "x86".

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160722191920.ej62fnspnqurbaa7@treble
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Always use host headers

From a conversation with Josh:

From http://lkml.kernel.org/r/20160722034118.guckaniobf3f7czc@treble :

It needs to be compiled with the host (powerpc) compiler, but then it
needs to disassemble target (x86) files.

----

So use HOSTARCH instead of ARCH.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20160722034118.guckaniobf3f7czc@treble
Link: http://lkml.kernel.org/n/tip-le1m1yzxnfpt3msbblu40nm8@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Use tools/scripts/Makefile.arch to get ARCH and HOSTARCH

objtool's Makefile was setting up ARCH but fixing up just the x86_64 ->
x86, using Makefile.arch will do the necessary fixups for all arches.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-hbq0bbh03u2b722vozcyql31@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Add -I$(srctree)/tools/arch/$(ARCH)/include/uapi

So that it can find asm/bitsperlong.h to get the __BITS_PER_LONG
definition.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-pr3pvskh65pey4po7t122z4j@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Avoid checking code drift on busybox's diff

That doesn't have -I to match lines.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-1zqv1h6okt70e2huokkdtf1u@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

objtool: Allow building with older libelf

The switch to elf_getshdr{num,strndx} post-dates the oldest tool chain
the kernel is supposed to be able to build with, so try to cope with
such an environment.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: <stable@vger.kernel.org> # for v4.6
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/732dae6872b7ff187d94f22bb699a12849d3fe04.1463430618.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Compile with debugging symbols

Compile objtool with debugging symbols ('-g') to help tools like perf
and gdb understand what it's doing. Combined with '-O2', it's not
always helpful, but it's better than nothing.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/c295e9ee9ed360dc8b2e1d180c859f11cfc151ef.1457502970.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Support CROSS_COMPILE

When building with CONFIG_STACK_VALIDATION on a ppc64le host with an x86
cross-compiler, Stephen Rothwell saw the following objtool build errors:

DESCEND objtool
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/builtin-check.o
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/special.o
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/elf.o
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/objtool.o
MKDIR /home/sfr/next/x86_64_allmodconfig/tools/objtool/arch/x86/insn/
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/libstring.o
elf.c:22:23: fatal error: sys/types.h: No such file or directory
compilation terminated.
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/exec-cmd.o
CC /home/sfr/next/x86_64_allmodconfig/tools/objtool/help.o
builtin-check.c:28:20: fatal error: string.h: No such file or directory
compilation terminated.
objtool.c:28:19: fatal error: stdio.h: No such file or directory
compilation terminated.

It fails to build because it tries to compile objtool with the
cross-compiler instead of the host compiler.

Ensure that it always uses the host compiler by ignoring CROSS_COMPILE.

In order to do that properly, the libsubcmd.a library needs to be built
in tools/objtool/ rather than tools/lib/subcmd/. The latter directory
contains the cross-compiled version which is needed for perf and
possibly other tools.

Note that cross-compiling for x86 on a _big_ endian system would result
in a bunch of false positive objtool warnings during the kernel build
because it isn't endian-aware. But that's generally a rare edge case
and there haven't been any reports of anybody needing that.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/55b63eefc347f1bb28573f972d8d1adbf1f1c31d.1456962210.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

objtool: Add tool to perform compile-time stack metadata validation

This adds a host tool named objtool which has a "check" subcommand which
analyzes .o files to ensure the validity of stack metadata. It enforces
a set of rules on asm code and C inline assembly code so that stack
traces can be reliable.

For each function, it recursively follows all possible code paths and
validates the correct frame pointer state at each instruction.

It also follows code paths involving kernel special sections, like
.altinstructions, __jump_table, and __ex_table, which can add
alternative execution paths to a given instruction (or set of
instructions). Similarly, it knows how to follow switch statements, for
which gcc sometimes uses jump tables.

Here are some of the benefits of validating stack metadata:

a) More reliable stack traces for frame pointer enabled kernels

Frame pointers are used for debugging purposes. They allow runtime
code and debug tools to be able to walk the stack to determine the
chain of function call sites that led to the currently executing
code.

For some architectures, frame pointers are enabled by
CONFIG_FRAME_POINTER. For some other architectures they may be
required by the ABI (sometimes referred to as "backchain pointers").

For C code, gcc automatically generates instructions for setting up
frame pointers when the -fno-omit-frame-pointer option is used.

But for asm code, the frame setup instructions have to be written by
hand, which most people don't do. So the end result is that
CONFIG_FRAME_POINTER is honored for C code but not for most asm code.

For stack traces based on frame pointers to be reliable, all
functions which call other functions must first create a stack frame
and update the frame pointer. If a first function doesn't properly
create a stack frame before calling a second function, the *caller*
of the first function will be skipped on the stack trace.

For example, consider the following example backtrace with frame
pointers enabled:

[<ffffffff81812584>] dump_stack+0x4b/0x63
[<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
[<ffffffff8127f568>] seq_read+0x108/0x3e0
[<ffffffff812cce62>] proc_reg_read+0x42/0x70
[<ffffffff81256197>] __vfs_read+0x37/0x100
[<ffffffff81256b16>] vfs_read+0x86/0x130
[<ffffffff81257898>] SyS_read+0x58/0xd0
[<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

It correctly shows that the caller of cmdline_proc_show() is
seq_read().

If we remove the frame pointer logic from cmdline_proc_show() by
replacing the frame pointer related instructions with nops, here's
what it looks like instead:

[<ffffffff81812584>] dump_stack+0x4b/0x63
[<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
[<ffffffff812cce62>] proc_reg_read+0x42/0x70
[<ffffffff81256197>] __vfs_read+0x37/0x100
[<ffffffff81256b16>] vfs_read+0x86/0x130
[<ffffffff81257898>] SyS_read+0x58/0xd0
[<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

Notice that cmdline_proc_show()'s caller, seq_read(), has been
skipped. Instead the stack trace seems to show that
cmdline_proc_show() was called by proc_reg_read().

The benefit of "objtool check" here is that because it ensures that
*all* functions honor CONFIG_FRAME_POINTER, no functions will ever[*]
be skipped on a stack trace.

[*] unless an interrupt or exception has occurred at the very
beginning of a function before the stack frame has been created,
or at the very end of the function after the stack frame has been
destroyed. This is an inherent limitation of frame pointers.

b) 100% reliable stack traces for DWARF enabled kernels

This is not yet implemented. For more details about what is planned,
see tools/objtool/Documentation/stack-validation.txt.

c) Higher live patching compatibility rate

This is not yet implemented. For more details about what is planned,
see tools/objtool/Documentation/stack-validation.txt.

To achieve the validation, "objtool check" enforces the following rules:

1. Each callable function must be annotated as such with the ELF
function type. In asm code, this is typically done using the
ENTRY/ENDPROC macros. If objtool finds a return instruction
outside of a function, it flags an error since that usually indicates
callable code which should be annotated accordingly.

This rule is needed so that objtool can properly identify each
callable function in order to analyze its stack metadata.

2. Conversely, each section of code which is *not* callable should *not*
be annotated as an ELF function. The ENDPROC macro shouldn't be used
in this case.

This rule is needed so that objtool can ignore non-callable code.
Such code doesn't have to follow any of the other rules.

3. Each callable function which calls another function must have the
correct frame pointer logic, if required by CONFIG_FRAME_POINTER or
the architecture's back chain rules. This can by done in asm code
with the FRAME_BEGIN/FRAME_END macros.

This rule ensures that frame pointer based stack traces will work as
designed. If function A doesn't create a stack frame before calling
function B, the _caller_ of function A will be skipped on the stack
trace.

4. Dynamic jumps and jumps to undefined symbols are only allowed if:

a) the jump is part of a switch statement; or

b) the jump matches sibling call semantics and the frame pointer has
the same value it had on function entry.

This rule is needed so that objtool can reliably analyze all of a
function's code paths. If a function jumps to code in another file,
and it's not a sibling call, objtool has no way to follow the jump
because it only analyzes a single file at a time.

5. A callable function may not execute kernel entry/exit instructions.
The only code which needs such instructions is kernel entry code,
which shouldn't be be in callable functions anyway.

This rule is just a sanity check to ensure that callable functions
return normally.

It currently only supports x86_64. I tried to make the code generic so
that support for other architectures can hopefully be plugged in
relatively easily.

On my Lenovo laptop with a i7-4810MQ 4-core/8-thread CPU, building the
kernel with objtool checking every .o file adds about three seconds of
total build time. It hasn't been optimized for performance yet, so
there are probably some opportunities for better build performance.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/f3efb173de43bd067b060de73f856567c0fa1174.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>