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Frank Wille | 4 Jan 2008 20:30
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Xamiga segfaults with 16 bit on CV64

Hi,

either it's me having done something stupid, or the Xamiga of 4.0 no longer
supports 16 bit screen depths. This is what I did:

---8<---
frank <at> phoenix grfconfig /dev/grf5
 1: 800x600x8   57.0kHz  <at>  92Hz flags: +hsync +vsync
 2: 800x600x16  57.8kHz  <at>  90Hz flags: +hsync +vsync
 3: 1024x768x8  72.8kHz  <at>  92Hz flags: default
 4: 1024x768x16 67.2kHz  <at>  83Hz flags: default
 5: 1152x900x8  68.9kHz  <at>  74Hz flags: default
 6: 1152x900x16 62.1kHz  <at>  66Hz flags: default
Console: 640x480 (80x60)        31.2kHz  <at>  59Hz flags: default
frank <at> phoenix cat .xserverrc 
X -dev /dev/grf5 -mode 2

frank <at> phoenix startx

The XKEYBOARD keymap compiler (xkbcomp) reports:
> Error:            Can't find file "amiga" for symbols include
>                   Exiting
>                   Abandoning symbols file "usa1"
Errors from xkbcomp are not fatal to the X server
Could not init font path element /usr/X11R6/lib/X11/fonts/CID/, removing from list!
X connection to :0.0 broken (explicit kill or server shutdown).
[1]   Segmentation fault      X -dev /dev/grf5...
---8<---

Further experiments have shown that it segfaults for mode 2, 4 and 6, but
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Frank Wille | 6 Jan 2008 14:43
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Re: Xamiga segfaults with 16 bit on CV64

Hi,

I'm crossposting to port-m68k, because gcc4 compiler bugs may be interesting
for all 68k ports.

Here are some more information about my Xserver crash.

Stack frame backtrace:

#0  0x00091be2 in cfb16FillBoxTile32sCopy ()
#1  0x0008a8b0 in cfb16FillBoxTileOdd ()
#2  0x00088222 in cfb16PaintWindow ()
#3  0x0010ed34 in miWindowExposures ()
#4  0x00025fc0 in MapWindow ()
#5  0x00026106 in InitRootWindow ()
#6  0x0000686a in main ()
#7  0x00005de4 in __start ()

The registers:

d0             0x0      0
d1             0x2      2
d2             0x1      1
d3             0x178500 1541376
d4             0x5      5
d5             0xdffecb4        234876084
d6             0x60dec  396780
d7             0x2037c  131964
a0             0x0      0x0
a1             0x178500 0x178500
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David Laight | 6 Jan 2008 15:12
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Re: Xamiga segfaults with 16 bit on CV64

On Sun, Jan 06, 2008 at 02:43:00PM +0100, Frank Wille wrote:
> 
> Disassembly of the crash location:
> [...]
> 0x91bd4 <cfb16FillBoxTile32sCopy+56>:   moveal %a1 <at> (16),%a0
> 0x91bd8 <cfb16FillBoxTile32sCopy+60>:   movel %a1,%sp <at> -
> 0x91bda <cfb16FillBoxTile32sCopy+62>:   moveal %a0 <at> (372),%a0
> 0x91bde <cfb16FillBoxTile32sCopy+66>:   jsr %a0 <at> 
> 0x91be0 <cfb16FillBoxTile32sCopy+68>:   addql #4,%sp
> 0x91be2 <cfb16FillBoxTile32sCopy+70>:   movel %a0 <at> (32),%fp <at> (-24)  <-- HERE
> [...]
> 
> The code looks to me like a compiler bug (unless the sub-routine is meant to
> return a result in a0). Register a0 is reused for deferencing after a sub-
> routine call, although it is definitely a volatile register (and zero after
> returning from the sub-routine).

%a0 is used to return a pointer from a function.
So it looks as though the called function returned 'NULL' and it wasn't
checked for.

	David

--

-- 
David Laight: david <at> l8s.co.uk
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Frank Wille | 6 Jan 2008 16:05
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Re: Xamiga segfaults with 16 bit on CV64

David Laight wrote:

> On Sun, Jan 06, 2008 at 02:43:00PM +0100, Frank Wille wrote:
>> 
>> Disassembly of the crash location: [...]
>> 0x91bd4 <cfb16FillBoxTile32sCopy+56>: moveal %a1 <at> (16),%a0 0x91bd8
>> <cfb16FillBoxTile32sCopy+60>: movel %a1,%sp <at> - 0x91bda
>> <cfb16FillBoxTile32sCopy+62>: moveal %a0 <at> (372),%a0 0x91bde
>> <cfb16FillBoxTile32sCopy+66>: jsr %a0 <at>  0x91be0
>> <cfb16FillBoxTile32sCopy+68>: addql #4,%sp 0x91be2
>> <cfb16FillBoxTile32sCopy+70>: movel %a0 <at> (32),%fp <at> (-24) <-- HERE [...]
>> 
>> The code looks to me like a compiler bug (unless the sub-routine is meant
>> to return a result in a0). Register a0 is reused for deferencing after a
>> sub- routine call, although it is definitely a volatile register (and
>> zero after returning from the sub-routine).
> 
> %a0 is used to return a pointer from a function.
> So it looks as though the called function returned 'NULL' and it wasn't
> checked for.

Thanks for the explanation. I wasn't aware that NetBSD follows a different ABI
than AmigaOS, which always uses d0 for return values.

Then I have to find out which function pointer is NULL here...

--

-- 
    _  Frank Wille (frank <at> phoenix.owl.de)
 _ //  http://sun.hasenbraten.de/~frank/
 \X/   Phx  <at>  #AmigaGer
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David Laight | 6 Jan 2008 17:23
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Re: Xamiga segfaults with 16 bit on CV64

On Sun, Jan 06, 2008 at 04:05:27PM +0100, Frank Wille wrote:
> > 
> > %a0 is used to return a pointer from a function.
> > So it looks as though the called function returned 'NULL' and it wasn't
> > checked for.
> 
> Thanks for the explanation. I wasn't aware that NetBSD follows a different ABI
> than AmigaOS, which always uses d0 for return values.

I only know because of the recent issues with the return value from mmap().

	David

--

-- 
David Laight: david <at> l8s.co.uk
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Martin Husemann | 6 Jan 2008 17:23
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Re: Xamiga segfaults with 16 bit on CV64

On Sun, Jan 06, 2008 at 04:05:27PM +0100, Frank Wille wrote:
> Thanks for the explanation. I wasn't aware that NetBSD follows a different ABI
> than AmigaOS, which always uses d0 for return values.

We use the SVR4 m68k ABI with ELF.

Martin
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