linux-kernel - Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID block count and size helpers")

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Message-ID: <YpIR67FMtTGCwARZ@debian>
Date:   Sat, 28 May 2022 13:13:31 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jani Nikula <jani.nikula@...el.com>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: mainline build failure due to f1e4c916f97f ("drm/edid: add EDID
 block count and size helpers")

On Fri, May 27, 2022 at 06:04:14PM -0700, Linus Torvalds wrote:
> On Fri, May 27, 2022 at 4:41 PM Sudip Mukherjee
> <sudipm.mukherjee@...il.com> wrote:
> >
> > I just tested with various values, sizeof(*edid) is 144 bytes at that place.
> 
> Hmm. What compiler do you have? Because it seems very broken.
> 
> You don't actually have to try with various sizes, you could have just
> done something like
> 
>  int size_of_edid(const struct edid *edid)
>  {
>         return sizeof(*edid);
>  }
> 
> and then "make drivers/gpu/drm/drm_edid.s" to generate assembly and
> see what it looks like (obviously removing the BUG_ON() in order to
> build).

just tried this with
make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- drivers/gpu/drm/drm_edid.s

> 
> That obviously generates code like
> 
>         movl    $128, %eax
>         ret

and for me it looks like:

.L1030: 
        .word   .LC40
        .word   .LC41
        .word   -1431655765
        .word   .LC39
        .size   drm_edid_to_sad, .-drm_edid_to_sad
        .align  2
        .global size_of_edid
        .syntax unified
        .arm
        .type   size_of_edid, %function
size_of_edid:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 1, uses_anonymous_args = 0
        mov     ip, sp  @,
        push    {fp, ip, lr, pc}        @
        sub     fp, ip, #4      @,,
@ drivers/gpu/drm/drm_edid.c:1573: }
        mov     r0, #144        @,
        ldmfd   sp, {fp, sp, pc}        @
        .size   size_of_edid, .-size_of_edid



--
Regards
Sudip