Re: [PATCH v9 15/17] media: rkvdec: Add H264 support for the VDPU383 variant

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Jan 21, 2026 at 09:46:48AM -0500, Nicolas Dufresne wrote:
> Le mercredi 21 janvier 2026 à 22:27 +0800, kernel test robot a écrit :
> > Hi Detlev,
> > 
> > kernel test robot noticed the following build warnings:
> > 
> > [auto build test WARNING on rockchip/for-next]
> > [also build test WARNING on linuxtv-media-pending/master media-tree/master linus/master v6.19-rc6 next-20260120]
> > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > And when submitting patch, we suggest to use '--base' as documented in
> > https://git-scm.com/docs/git-format-patch#_base_tree_information]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Detlev-Casanova/media-uapi-HEVC-Add-v4l2_ctrl_hevc_ext_sps_-ls-t_rps-controls/20260121-071026
> > base:   https://git.kernel.org/pub/scm/linux/kernel/git/mmind/linux-rockchip.git for-next
> > patch link:    https://lore.kernel.org/r/20260120222018.404741-16-detlev.casanova%40collabora.com
> > patch subject: [PATCH v9 15/17] media: rkvdec: Add H264 support for the VDPU383 variant
> > config: loongarch-allmodconfig (https://download.01.org/0day-ci/archive/20260121/202601211924.rqKS2Ihm-lkp@intel.com/config)
> > compiler: clang version 19.1.7 (https://github.com/llvm/llvm-project cd708029e0b2869e80abe31ddb175f7c35361f90)
> 
> Modification has been done to reduce the stack utilization on clang, though we
> believe we are hitting limitations/bugs on older clang. We went ahead with these
> patch by updating our CI to clang 21, which allocate a lot less stack with KASAN
> enabled and this code. Our general advise is to use a newer clang, or GCC for
> testing with KASAN.
> 
> The stack utilization is caused by the combination of loop unrolling, agressive
> inlining, and write operations to bitfield (which requires the compiler to
> generate more code for memory checks, since the writes are not aligned).

Yes, this is an area that has known pain points, even in current
versions (but it is certainly better in most cases):

https://github.com/llvm/llvm-project/issues/143908
https://github.com/llvm/llvm-project/issues/115862

Thank you for working around this.

Cheers,
Nathan