Date:   Mon, 13 Aug 2018 10:48:57 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Christian Koenig <christian.koenig@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "Deucher, Alexander" <alexander.deucher@....com>,
        Chunming Zhou <David1.Zhou@....com>,
        "Wentland, Harry" <Harry.Wentland@....com>,
        Dave Airlie <airlied@...ux.ie>,
        "Daenzer, Michel" <michel.daenzer@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        "S, Shirish" <shirish.s@....com>, Jerry Zuo <Jerry.Zuo@....com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH] [v3] drm: amd: dc: don't use FP math when Kcov is enabled

On Sun, Aug 12, 2018 at 3:55 AM Christian König
<ckoenig.leichtzumerken@...il.com> wrote:
>
> Adding Harry as well.
>
> Am 11.08.2018 um 17:54 schrieb Arnd Bergmann:
> > Building the DCN 1.0 Raven display driver with CONFIG_KCOV_INSTRUMENT_ALL=y
> > and CONFIG_KCOV_ENABLE_COMPARISONS=y results in warnings about many functions
> > that do a comparison of floating-point variables:
> >
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_bw_calc_rq_dlg_ttu':
> > dcn_calcs.c:(.text+0x263): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `hack_force_pipe_split':
> > dcn_calcs.c:(.text+0x155b): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_find_dcfclk_suits_all':
> > dcn_calcs.c:(.text+0x190e): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calcs.o: In function `dcn_validate_bandwidth':
> > dcn_calcs.c:(.text+0xe121): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_mod':
> > dcn_calc_math.c:(.text+0x22): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_min2':
> > dcn_calc_math.c:(.text+0xb2): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_ceil2':
> > dcn_calc_math.c:(.text+0x2a0): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_max3':
> > dcn_calc_math.c:(.text+0x325): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_max5':
> > dcn_calc_math.c:(.text+0x3c3): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_math.o: In function `dcn_bw_log':
> > dcn_calc_math.c:(.text+0x54e): undefined reference to `__sanitizer_cov_trace_cmpd'
> > dcn_calc_math.c:(.text+0x57c): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `scaler_settings_calculation':
> > dcn_calc_auto.c:(.text+0x5c5): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
> > dcn_calc_auto.c:(.text+0x137c): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
> > dcn_calc_auto.c:(.text+0x9233): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
> > dcn_calc_auto.c:(.text+0xb70f): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `mode_support_and_system_configuration':
> > dcn_calc_auto.c:(.text+0x121fd): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `display_pipe_configuration':
> > dcn_calc_auto.c:(.text+0x15a2f): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
> > dcn_calc_auto.c:(.text+0x17c2d): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
> > dcn_calc_auto.c:(.text+0x19362): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
> > dcn_calc_auto.c:(.text+0x25575): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/calcs/dcn_calc_auto.o: In function `dispclkdppclkdcfclk_deep_sleep_prefetch_parameters_watermarks_and_performance_calculation':
> > dcn_calc_auto.c:(.text+0x27f33): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `get_refcyc_per_delivery':
> > display_rq_dlg_calc.c:(.text+0xb5): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `calculate_ttu_cursor.isra.1':
> > display_rq_dlg_calc.c:(.text+0x9f6): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/display_rq_dlg_calc.o: In function `dml_rq_dlg_get_dlg_params':
> > display_rq_dlg_calc.c:(.text+0x82cc): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_refcyc_per_delivery.isra.0':
> > dml1_display_rq_dlg_calc.c:(.text+0x6c4): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_vratio_pre.isra.2':
> > dml1_display_rq_dlg_calc.c:(.text+0x957): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `get_swath_need.isra.3':
> > dml1_display_rq_dlg_calc.c:(.text+0xc8e): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_extract_rq_regs':
> > dml1_display_rq_dlg_calc.c:(.text+0x30a8): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_rq_dlg_get_dlg_params':
> > dml1_display_rq_dlg_calc.c:(.text+0x41ee): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/dml1_display_rq_dlg_calc.o: In function `dml1_rq_dlg_get_dlg_params':
> > dml1_display_rq_dlg_calc.c:(.text+0x8f95): undefined reference to `__sanitizer_cov_trace_cmpf'
> > drivers/gpu/drm/amd/display/dc/dml/dml_common_defs.o: In function `dml_round':
> > dml_common_defs.c:(.text+0x77): undefined reference to `__sanitizer_cov_trace_cmpd'
> > drivers/gpu/drm/amd/display/dc/dml/display_mode_vba.o: In function `adjust_ReturnBW':
> > display_mode_vba.c:(.text+0x4490): undefined reference to `__sanitizer_cov_trace_cmpd'
> >
> > We already prevent the driver from being built on non-x86 architectures
> > because of its use of floating-point arithmetic, this extends the
> > dependency to also cover Kcov-enabled builds, which arguably is a much
> > more severe limitation.
> >
> > I tried implementing the two functions in KCOV: __sanitizer_cov_trace_cmpd
> > and __sanitizer_cov_trace_cmpf, but that fails to build on architectures
> > that do not support any floating-point functions, or would require making
> > that code x86 specific as well.  I also looked at what it would take to
> > convert the code to fixed-point arithmetic, but quickly gave up. This
> > is probably the right approach, but it requires a non-trivial amount of
> > work and certainly won't be appropriate as a bugfix.
> >
> > Fixes: bf2e2e2e0ea9 ("drm/amd/display: Limit DCN to x86 arch")
> > Fixes: 4841203102a3 ("drm/amdgpu/display: Replace CONFIG_DRM_AMD_DC_DCN1_0 with CONFIG_X86")

Maybe it would be better to revert 4841203102a3 so we can limit the
scope of this to DCN support.

Alex


> > Link: drm: amd: dc: don't use FP math when Kcov is enabled
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > ---
> > v3: rebase on top of 4841203102a3, which removed the option for
> > CONFIG_DRM_AMD_DC_DCN1_0. The problem still gets hit occasionally
> > in randconfig testing.
> > ---
> >   drivers/gpu/drm/amd/display/Kconfig | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/amd/display/Kconfig b/drivers/gpu/drm/amd/display/Kconfig
> > index 325083b0297e..b132d434e572 100644
> > --- a/drivers/gpu/drm/amd/display/Kconfig
> > +++ b/drivers/gpu/drm/amd/display/Kconfig
> > @@ -3,6 +3,7 @@ menu "Display Engine Configuration"
> >
> >   config DRM_AMD_DC
> >       bool "AMD DC - Enable new display engine"
> > +     depends on !X86 || !(KCOV_INSTRUMENT_ALL && KCOV_ENABLE_COMPARISONS) || BROKEN
> >       default y
> >       help
> >         Choose this option if you want to use the new display engine
>
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