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Linus Torvalds 47f15561b6 drm: fix EDID struct for old ARM OABI format 
When building the kernel for arm with the "-mabi=apcs-gnu" option, gcc
will force alignment of all structures and unions to a word boundary
(see also STRUCTURE_SIZE_BOUNDARY and the "-mstructure-size-boundary=XX"
option if you're a gcc person), even when the members of said structures
do not want or need said alignment.

This completely messes up the structure alignment of 'struct edid' on
those targets, because even though all the embedded structures are
marked with "__attribute__((packed))", the unions that contain them are
not.

This was exposed by commit f1e4c916f9 ("drm/edid: add EDID block count
and size helpers"), but the bug is pre-existing.  That commit just made
the structure layout problem cause a build failure due to the addition
of the

        BUILD_BUG_ON(sizeof(*edid) != EDID_LENGTH);

sanity check in drivers/gpu/drm/drm_edid.c:edid_block_data().

This legacy union alignment should probably not be used in the first
place, but we can fix the layout by adding the packed attribute to the
union entries even when each member is already packed and it shouldn't
matter in a sane build environment.

You can see this issue with a trivial test program:

  union {
	struct {
		char c[5];
	};
	struct {
		char d;
		unsigned e;
	} __attribute__((packed));
  } a = { "1234" };

where building this with a normal "gcc -S" will result in the expected
5-byte size of said union:

	.type	a, @object
	.size	a, 5

but with an ARM compiler and the old ABI:

    arm-linux-gnu-gcc -mabi=apcs-gnu -mfloat-abi=soft -S t.c

you get

	.type	a, %object
	.size	a, 8

instead, because even though each member of the union is packed, the
union itself still gets aligned.

This was reported by Sudip for the spear3xx_defconfig target.

Link: https://lore.kernel.org/lkml/YpCUzStDnSgQLNFN@debian/
Reported-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2022-05-28 13:06:49 -07:00
arch hyperv-next for 5.19 2022-05-28 11:39:01 -07:00
block Page cache changes for 5.19 2022-05-24 19:55:07 -07:00
certs Kbuild updates for v5.19 2022-05-26 12:09:50 -07:00
crypto This update includes the following changes: 2022-05-27 18:06:49 -07:00
Documentation powerpc updates for 5.19 2022-05-28 11:27:17 -07:00
drivers hyperv-next for 5.19 2022-05-28 11:39:01 -07:00
fs powerpc updates for 5.19 2022-05-28 11:27:17 -07:00
include drm: fix EDID struct for old ARM OABI format 2022-05-28 13:06:49 -07:00
init Two followon fixes for the post-5.19 series "Use pageblock_order for cma 2022-05-27 11:40:49 -07:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-05-09 18:29:21 -07:00
kernel cxl for 5.19 2022-05-27 21:24:19 -07:00
lib Revert "crypto: poly1305 - cleanup stray CRYPTO_LIB_POLY1305_RSIZE" 2022-05-28 10:04:06 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm powerpc updates for 5.19 2022-05-28 11:27:17 -07:00
net hyperv-next for 5.19 2022-05-28 11:39:01 -07:00
samples drm for 5.19-rc1 2022-05-25 16:18:27 -07:00
scripts Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
security linux-kselftest-kunit-5.19-rc1 2022-05-25 11:32:53 -07:00
sound sound updates for 5.19-rc1 2022-05-25 16:55:16 -07:00
tools powerpc updates for 5.19 2022-05-28 11:27:17 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt S390: 2022-05-26 14:20:14 -07:00
.clang-format clang-format: Fix space after for_each macros 2022-05-20 19:27:16 +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 kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Scheduler changes in this cycle were: 2022-05-24 11:11:13 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
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 Pin control bulk changes for the v5.19 series: 2022-05-28 11:15:54 -07:00
Makefile Kbuild updates for v5.19 2022-05-26 12:09:50 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.