Re: mainline build failure due to 5d8c3e836fc2 ("drm/amd/display: fix array-bounds error in dc_stream_remove_writeback()")

From: Sudip Mukherjee
Date: Thu Oct 06 2022 - 16:51:19 EST

On Thu, Oct 6, 2022 at 9:37 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Thu, Oct 06, 2022 at 12:39:40PM -0700, Linus Torvalds wrote:
> > What confuses me is that error message ("array subscript [0, 0] is
> > outside array bounds of 'struct dc_writeback_info[1]') which seems to
> > be aware that the value is actually 0.
> I've seen bugs in the tracker where the reporting is broken but the
> range checker is working "correctly", which seems to be the case here.
> > If somebody cannot come up with a fix, I suspect the solution is "gcc
> > array bounds analysis is terminally buggy" and we just need to disable
> > it for gcc-11 too.
> It does continue to find bugs, so I'd rather keep it on. GCC has fixed
> all the issues we've run into so far (though not all have been back
> ported to GCC 12 yet, so yes, let's keep -Warray-bounds disabled there).
> Specifically, I've been tracking:
> Fixed 13+
> Fixed 12+, 11.3

Thats odd, the bug report says its fixed but I am using:
gcc version 11.3.1 20220925 (GCC)

> And it looks like Sudip's proposed fix for this particular code is
> additionally fixing unsigned vs signed as well. I think -Warray-bounds
> did its job (though, with quite a confusing index range in the report).

Not my. Linus's. I just tested. :)