__declspec(naked) and function body size

[Ilyes Gouta]

Hi,

Thank you so much, Brian, for your help.
I'm going to try this out and see if it fits my requirements.

BR,
Ilyes Gouta.

Brian Dessent wrote:
> Ilyes Gouta wrote:
> 
>> Is it possible to get the size of a function, i.e the number of bytes generated by the compiler between the prologue and
>> the final routine's ret instruction, so that it would be available through a 'sizeof' like operator for the other code?
> 
> You can do this at the assembler level:
> 
> int foo()
> {
>   int a = 0, b = 1;
>   int c = a + b;
> 
>   return (c);
> }
> 
> asm(".set foo_size, .-foo");
> extern unsigned foo_size;                
> 
> int main()
> {
>   unsigned char buf[512];
> 
>   memcpy (buf, foo, foo_size);
> }
> 
> There are two problems with this:
> 
> 1. In unit-at-a-time mode (which is enabled by default when optimizing)
> the compiler does not guarantee that functions and top-level asm
> statements are emitted in the same order as specified in the input
> source.  Since this technique requires that the asm() come immediately
> after the function it refers to, this will break.  So you have to use
> -fno-unit-at-a-time (for gcc < 4.2.0) or preferably
> -fno-toplevel-reorder (for gcc >= 4.2.0) unless you use -O0.
> 
> 2. The asm has to be adjusted if you want it to work on
> leading-underscore targets.  For example on win32 you'd need to use
> something like asm(".set _foo_size, .-_foo") instead.  I suppose you
> could abstract this away with some macro junk:
> 
> #define ASMNAME(cname)          ASMNAME2 (__USER_LABEL_PREFIX__, cname)
> #define ASMNAME2(prefix, cname) STRING (prefix) cname
> #define STRING(x)               #x
> 
> // ...
> 
> asm(".set " ASMNAME("foo_size") ", .-" ASMNAME("foo"));
> extern unsigned foo_size;
> 
> Brian
>