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Marco Elver 75d75b7a4d kcsan: Support distinguishing volatile accesses
In the kernel, the "volatile" keyword is used in various concurrent
contexts, whether in low-level synchronization primitives or for
legacy reasons. If supported by the compiler, it will be assumed
that aligned volatile accesses up to sizeof(long long) (matching
compiletime_assert_rwonce_type()) are atomic.

Recent versions of Clang [1] (GCC tentative [2]) can instrument
volatile accesses differently. Add the option (required) to enable the
instrumentation, and provide the necessary runtime functions. None of
the updated compilers are widely available yet (Clang 11 will be the
first release to support the feature).

[1] 5a2c31116f
[2] https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544452.html

This change allows removing of any explicit checks in primitives such as
READ_ONCE() and WRITE_ONCE().

 [ bp: Massage commit message a bit. ]

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200521142047.169334-4-elver@google.com
2020-06-11 20:04:01 +02:00
arch Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
block for-5.8/drivers-2020-06-01 2020-06-02 15:37:03 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux 2020-06-10 14:46:54 -07:00
Documentation Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
drivers Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
fs Merge branch 'work.epoll' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-06-10 18:09:13 -07:00
include Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
init Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel kcsan: Support distinguishing volatile accesses 2020-06-11 20:04:01 +02:00
lib kcsan: Restrict supported compilers 2020-06-11 20:04:00 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
net Merge branch 'work.sysctl' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-06-10 16:05:54 -07:00
samples Kbuild updates for v5.8 2020-06-06 12:00:25 -07:00
scripts kcsan: Support distinguishing volatile accesses 2020-06-11 20:04:01 +02:00
security overlayfs update for 5.8 2020-06-09 15:40:50 -07:00
sound mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
tools Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
Makefile Rebase locking/kcsan to locking/urgent 2020-06-11 20:02:46 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.