[Vm-dev] SIZEOF_VOID_P 8 and mprotect

[David T. Lewis]

On Wed, Jul 09, 2014 at 11:56:59AM -0700, gettimothy wrote:
>  
> Hi All.
> 
> 
> Don't spend brain cycles on this, but I want to mention it in passing.

Hi tty,

The Cog VMs cannot be compiled in 32-bit mode, so if you are on a 64-bit platform the
CFLAGS will need to specify -m32 to tell the compiler to use the 32 bit memory model.
If you pass the right CFLAGS (with "-m32") to platforms/unix/cmake/configure, you will
find that the generated config.h will have the correct type definitions.

CMake takes care of the rest. But if you want to explicitly tell it to use a 32-bit
memory model (required for Cog), you will want this to happen at the "configure" step
so that config.h is defined properly for a 32-bit build. That is the reason that the
CFLAGS are specified as an option to unix/cmake/configure, and it is the reason that
config.h is generated at this point in the configure/make process.

Dave

> 
> 
> I am working out integrating Ian's configuration approach into the CMakeVMakerSqueak and ran into this interesting thing.
> 
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> Ian's code on my system will detect the SIZEOF_ stuff on my system
> 
> 
> 
> #define SIZEOF_INT 4
> 
> #define SIZEOF_LONG 8
> #define SIZEOF_LONG_LONG 8
> #define SIZEOF_VOID_P 8
> 
>  
> When I go to run the cog, I get this error.
> 
> 
> 
> mprotect(x,y,PROT_READ | PROT_WRITE | PROT_EXEC): Cannot allocate memory
> Segmentation fault (core dumped)
> 
> 
>  
> 
> 
> Changing SIZEOF_VOID_P to 4 makes that problem go away and the image launches.
> 
> 
> I am thinking I am going to throw a conditional in the configuration such that if it is a 64 bit system with 32 bit libs, to work around this.
> 
> 
> I mention this in passing in case there is a "magic" 
> #define mprotect_will_just_work 1 
>  
> flag or something.
> 
> 
> 
> 
> cordially,
> 
> 
> tty
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