Re: [PATCH] drm/amdgpu: make DRM_AMD_DC x86-only again

[Nick Desaulniers]

On Tue, Dec 8, 2020 at 2:18 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> On Tue, Dec 8, 2020 at 7:21 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> >
> > On Tue, Dec 8, 2020 at 6:26 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Dec 7, 2020 at 11:28 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-linux@xxxxxxxxxxxxxxxx> wrote:
> > Hmm...no warnings for me with that config on next-20201208:
> > $ make LLVM=1 -j71 olddefconfig
> > $ make LLVM=1 -j71
> > ...
> > $ clang --version
> > clang version 12.0.0 (git@xxxxxxxxxx:llvm/llvm-project.git
> > 1c98f984105e552daa83ed8e92c61fba0e401410)
> > (ie. near ToT LLVM)
> >
> > I see CONFIG_KASAN=y in the .config, so that's a recurring theme with
> > clang; excessive stack usage.  It does seem a shame to disable a
> > driver for a bunch of archs just due to KASAN stack usage.
> > $ grep KASAN=y 0x9077925C_defconfig
> > CONFIG_HAVE_ARCH_KASAN=y
> > CONFIG_KASAN=y
> >
> > Is there a different branch of a different tree that I should be
> > testing on instead? Otherwise, can you send the object file?
>
> I was on a slightly older linux-next, and the latest version contains
> the patch "ubsan: enable for all*config builds" in linux-next,
> which enables CONFIG_UBSAN_SANITIZE_ALL. It took me
> an hour to figure out, but after turning that option off, the warning
> is back.
>
> I'll send you the object for reference in a private mail, it's kind
> of large.

Got it, thanks.

$ llvm-objdump -Dr
--disassemble-symbols=dml30_ModeSupportAndSystemConfigurationFull
display_mode_vba_30.o
...
   1584f: 48 81 ec a0 08 00 00          subq    $2208, %rsp
...
$ python3 /android0/frame-larger-than/frame_larger_than.py
display_mode_vba_30.o dml30_ModeSupportAndSystemConfigurationFull
No dwarf info found in display_mode_vba_30.o
$ llvm-readelf -S display_mode_vba_30.o | grep debug_info
$ echo $?
1

Can you rebuild+resend with CONFIG_DEBUG_INFO enabled?
frame_larger_than.py relies on the DWARF debug info to know what local
variables occupy how much stack space.
-- 
Thanks,
~Nick Desaulniers