llvm dev - Mar 2010 - [LLVMdev] Idea for Google Summer Code : C Compiler for EFI Byte Code implement in LLVM

On Mar 30, 2010, at 10:31 AM, 琬菁楊 wrote:
> What do you mean by "variable sized pointers"?  What does:
> 
> struct  S {void *X; };
> 
> return for sizeof(struct S); ?
> 
> I have surveyed the UEFI spec2.3.
> In my opinion, if the EBC VM is running on 32-bit processor, return value
is 4
> if the EBC VM is running on 64-bit processor, return value is 8
> 
> If error out on any sizeof that include a pointer, does it means that no
issue about pointer size determined at runtime??
Yes, if it is an error, it makes it much more feasible to implement.

-Chris
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On Mar 30, 2010, at 8:23 PM, Chris Lattner wrote:
> 
> On Mar 30, 2010, at 10:31 AM, 琬菁楊 wrote:
> 
>> What do you mean by "variable sized pointers"?  What does:
>> 
>> struct  S {void *X; };
>> 
>> return for sizeof(struct S); ?
>> 
>> I have surveyed the UEFI spec2.3.
>> In my opinion, if the EBC VM is running on 32-bit processor, return
value is 4
>> if the EBC VM is running on 64-bit processor, return value is 8
>> 
>> If error out on any sizeof that include a pointer, does it means that
no issue about pointer size determined at runtime??
> 
> Yes, if it is an error, it makes it much more feasible to implement.
But it is not an error, otherwise it would be hard to use malloc() like
functions.

2010/3/30 Chris Lattner <clattner at apple.com>:
> If error out on any sizeof that include a pointer, does it means that no
> issue about pointer size determined at runtime??
>
> Yes, if it is an error, it makes it much more feasible to implement.
I don't see why it should be that difficult.

If sizeof becomes an intrinsic that is called at runtime to determine
the pointer size (probably stored in some global or read from a
configuration register), than the problem is solved. If the types'
sizes change too, this intrinsic could accept a parameter (enum?) with
the type of the type.


cheers,
--renato

http://systemcall.org/

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Hi Tristan,

> But it is not an error, otherwise it would be hard to use malloc() like
> functions.
>
>
I cannot understand that it would be hard to use malloc() like functions
the parameter passed to malloc is evaluated at runtime
what is the issue of malloc when sizeof is determined at runtime?

thanks

ching
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