Re: [hatari-devel] Hatari segfault on cold boot with MMU + EmuTOS

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 11/1/18 11:48 PM, Nicolas Pomarède wrote:
> Le 01/11/2018 à 19:00, Nicolas Pomarède a écrit :
> > Le 01/11/2018 à 11:02, Nicolas Pomarède a écrit :
> > > I have an other PC which is still running linux 32 bit, I will try on 
> > > it too.
> >
> > good news is that I can duplicate the crash when using a 32 bit build.

Good.

With your latest update (which shouldn't affect this as I'm not using
TT-RAM), I'm not anymore able to reproduce the crash right after EmuTOS
bootup screen.  I get it only when pressing AltGr+C *after* EmuDesk
desktop has come up.


> > This looks like some memory being overwritten at some points, because 
> > when I add some debug printf, some of those printfs make the crash 
> > disappear ...
> >
> > So far, I see that the crash happens just after the reset, the 1st 
> > instruction after the reset get a bus error when being fetched.
> > I think it's a bug in hatari, because PC is not the correct value at 
> > this point, so when mmu is on, this calls mmu030_page_fault() and this 
> > is more or less where the crash happens (I still need to add more 
> > traces to see what part of the code can trigger the bus error).
> >
> > But I think the source of the bug is in Hatari, not in WinUAE.
>
> Additional note : it seems the crash happens when some optimisations are 
> enabled. cmake defaults will be -O3, but if I run "./configure 
> --enable-debug" and modify the debug section in CMakeList.txt to use 
> "-O0" instead of "-O", then I'm not able to crash hatari anymore.
> This really confirms that some memory must be leaking somewhere and its 
> impact/crash will depend on what region get overwritten.

-O0 keeps all variables in stack instead of using registers for them,
and doesn't do *any* other optimizations either, so the stack content
can be really different with it, than when optimizations are enabled.

It seems that GCC enables strict aliasing now even with -O2 & -Os.
Aliasing is one of the ways where code can shoot itself, but I don't
get any warnings with -Wstrict-aliasing (which should catch most, but
not all of potential issues).

Enabling -Wextra, complains just about missing field initializers
and things that might get clobbered by longjmp or vfork.  -Wshadow
complains mostly about very common names used by WinUAE core.

Of last one, the ones related to MMU use are:
-------------------------------------
hatari/src/cpu/memory.c: In function ‘memory_map_Standard_RAM’:
hatari/src/cpu/memory.c:1506:39: warning: declaration of 
‘MMU_Bank0_Size’ shadows a global declaration [-Wshadow]
 void memory_map_Standard_RAM ( Uint32 MMU_Bank0_Size , Uint32 
MMU_Bank1_Size )
                                       ^~~~~~~~~~~~~~
In file included from hatari/src/includes/ioMem.h:20:0,
                 from hatari/src/cpu/memory.c:24:
hatari/src/includes/stMemory.h:40:15: note: shadowed declaration is here
 extern Uint32 MMU_Bank0_Size;
               ^~~~~~~~~~~~~~
hatari/src/cpu/memory.c:1506:63: warning: declaration of 
‘MMU_Bank1_Size’ shadows a global declaration [-Wshadow]
 void memory_map_Standard_RAM ( Uint32 MMU_Bank0_Size , Uint32 
MMU_Bank1_Size )

^~~~~~~~~~~~~~
In file included from hatari/src/includes/ioMem.h:20:0,
                 from hatari/src/cpu/memory.c:24:
hatari/src/includes/stMemory.h:41:15: note: shadowed declaration is here
 extern Uint32 MMU_Bank1_Size;
               ^~~~~~~~~~~~~~
-------------------------------------

This looks also a bit suspect:
-------------------------------------
hatari/src/cpu/build68k.c: In function ‘main’:
hatari/src/cpu/build68k.c:83:19: warning: declaration of ‘flaguse’ 
shadows a global declaration [-Wshadow]
   int flagset[5], flaguse[5];
                   ^~~~~~~
In file included from hatari/src/cpu/build68k.c:10:0:
hatari/src/cpu/readcpu.h:62:13: note: shadowed declaration is here
 } ENUMNAME (flaguse);
             ^
hatari/src/cpu/sysdeps.h:274:24: note: in definition of macro ‘ENUMNAME’
 #define ENUMNAME(name) name
                        ^~~~
-------------------------------------


	- Eero