On Sat, 28 May 2022, Linus Torvalds torvalds@linux-foundation.org wrote:
On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann arnd@arndb.de wrote:
It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this option, you the kernel is built for the old 'OABI' that forces all non-packed struct members to be at least 16-bit aligned.
Looks like forced word (32 bit) alignment to me.
I wonder how many other structures that messes up, but I committed the EDID fix for now.
Thanks for the fix, and the thorough commit message!
This has presumably been broken for a long time, but maybe the affected targets don't typically use EDID and kernel modesetting, and only use some fixed display setup instead.
Those structure definitions go back a _loong_ time (from a quick 'git blame' I see November 2008).
But despite that, I did not mark my fix 'cc:stable' because I don't know if any of those machines affected by this bad arm ABI issue could possibly care.
At least my tree hopefully now builds on them, with the BUILD_BUG_ON() that uncovered this.
Indeed the bug is ancient. I just threw in the BUILD_BUG_ON() on a whim as an extra sanity check when doing pointer arithmetics on struct edid *.
If there are affected machines, buffer overflows are the real danger due to edid->extensions indicating the number of extensions.
BR, Jani.