Re: [PATCH] drm/amd/display: add -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines

[Nick Desaulniers]

Suggestions:
1. revert patch
2. get me the disassembly from gcc of the translation unit in question.
3. land patch that adds clang guards or something different based on 2.

Revert first; ask questions later.

On Tue, Jan 29, 2019 at 11:01 AM Wentland, Harry <Harry.Wentland@xxxxxxx> wrote:
>
> On 2019-01-29 1:56 p.m., Guenter Roeck wrote:
> > On Tue, Jan 29, 2019 at 10:30:31AM -0500, Alex Deucher wrote:
> >> On Fri, Jan 25, 2019 at 10:29 AM Wentland, Harry <Harry.Wentland@xxxxxxx> wrote:
> >>>
> >>> On 2019-01-24 7:52 p.m., ndesaulniers@xxxxxxxxxx wrote:
> >>>> arch/x86/Makefile disables SSE and SSE2 for the whole kernel.  The
> >>>> AMDGPU drivers modified in this patch re-enable SSE but not SSE2.  Turn
> >>>> on SSE2 to support emitting double precision floating point instructions
> >>>> rather than calls to non-existent (usually available from gcc_s or
> >>>> compiler_rt) floating point helper routines.
> >>>>
> >>>> Link: https://gcc.gnu.org/onlinedocs/gccint/Soft-float-library-routines.html
> >>>> Link: https://github.com/ClangBuiltLinux/linux/issues/327
> >>>> Cc: stable@xxxxxxxxxxxxxxx # 4.19
> >>>> Reported-by: S, Shirish <Shirish.S@xxxxxxx>
> >>>> Reported-by: Matthias Kaehlcke <mka@xxxxxxxxxx>
> >>>> Suggested-by: James Y Knight <jyknight@xxxxxxxxxx>
> >>>> Suggested-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
> >>>> Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> >>>> Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> >>>
> >>> Reviewed-by: Harry Wentland <harry.wentland@xxxxxxx>
> >>>
> >>> and applied.
> >>>
> >>
> >> This patch causes a segfault:
> >> https://bugs.freedesktop.org/show_bug.cgi?id=109487
> >>
> >> Any ideas?
> >>
> >
> > Set -msse2 only for clang ? I suspect, though, that this might only
> > solve the compile problem. If I understand correctly, the first
> > warning in the log is due to BREAK_TO_DEBUGGER(), suggesting that
> > something is seriously wrong. Maybe enabling sse2 results in different
> > results from floating point operations.
> >
> > Unfortunately I don't have a system with the affected GPU,
> > so I can't run any tests on real hardware. Unless someone can test
> > with real hardware, I think we have no choice but to revert the
> > patch.
> >
>
> Might be a good idea. Even though, best to revert for now until we understand what's going on.
>
> It seems like people at AMD building with gcc 5.4 are fine, but those using gcc 7.3 or 8.2 experience the crash.
>
> Harry
>
> > Guenter
> >
> >> Alex
> >>
> >>> Harry
> >>>
> >>>> ---
> >>>>  drivers/gpu/drm/amd/display/dc/calcs/Makefile | 2 +-
> >>>>  drivers/gpu/drm/amd/display/dc/dml/Makefile   | 2 +-
> >>>>  2 files changed, 2 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/amd/display/dc/calcs/Makefile b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
> >>>> index 95f332ee3e7e..dc85a3c088af 100644
> >>>> --- a/drivers/gpu/drm/amd/display/dc/calcs/Makefile
> >>>> +++ b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
> >>>> @@ -30,7 +30,7 @@ else ifneq ($(call cc-option, -mstack-alignment=16),)
> >>>>       cc_stack_align := -mstack-alignment=16
> >>>>  endif
> >>>>
> >>>> -calcs_ccflags := -mhard-float -msse $(cc_stack_align)
> >>>> +calcs_ccflags := -mhard-float -msse -msse2 $(cc_stack_align)
> >>>>
> >>>>  CFLAGS_dcn_calcs.o := $(calcs_ccflags)
> >>>>  CFLAGS_dcn_calc_auto.o := $(calcs_ccflags)
> >>>> diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> >>>> index d97ca6528f9d..33c7d7588712 100644
> >>>> --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
> >>>> +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> >>>> @@ -30,7 +30,7 @@ else ifneq ($(call cc-option, -mstack-alignment=16),)
> >>>>       cc_stack_align := -mstack-alignment=16
> >>>>  endif
> >>>>
> >>>> -dml_ccflags := -mhard-float -msse $(cc_stack_align)
> >>>> +dml_ccflags := -mhard-float -msse -msse2 $(cc_stack_align)
> >>>>
> >>>>  CFLAGS_display_mode_lib.o := $(dml_ccflags)
> >>>>  CFLAGS_display_pipe_clocks.o := $(dml_ccflags)
> >>>>
> >>> _______________________________________________
> >>> amd-gfx mailing list
> >>> amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> >>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx



-- 
Thanks,
~Nick Desaulniers