Re: [Qemu-devel] classic emulator Vs QEMU-TCG

[Stefano Bonifazi <stefboombastic@gmail.com>]

On 12/16/2010 04:57 PM, Mulyadi Santosa wrote:
> With my limited C knowledge, I saw that as a instruction jump (to
> tb_ptr). The "code_gen_prologue" seems to me like a cast..... casting
> each opcode in tb_ptr as uint8_t.... with maximum length=1024
Hi! Thank you for your reply!

I've got an explanation from a C guru :)

>((long REGPARM (*)(void *))code_gen_prologue)(tb_ptr)
>---------
>(long REGPARM (*)(void *)) is a type: a pointer pointing to a function, which takes one (void*) parameter. code_gen_prologue is an>array, array's name when used is considered to be a pointer to its first element, thus you are casting here pointer to the first byte of>array to pointer to function (...).
>Ellipsis with tb_ptr mean 'call function under this address and pass there whatever tb_ptr is'

Now everything is very clear for me :)
I do know pointer to functions, and if I had got:

>long REGPARM (*myfunc)(void *)

I would have recognized it.. but removing the function pointer name, 
leaving only the * was enough for me to be lost :[
also the definition of code_gen_prologue was tricky:
> uint8_t code_gen_prologue[1024] code_gen_section;
that code_gen_section at first confused my idea of a normal variable 
definition as "type identifier" .. until I found out it was a define for 
a compiler directive (alignment) :[

So inside code_gen_prologue array there is stored some function (in 
binary code) that takes a tb_ptr as argument and returns a long .. I 
have to check what it is inside there for understanding how the 
translated target code is run now ;)

> I hope that's the right interpretation...I must admit Qemu is full of
> gcc and C tricks here and there...
Yes! I've only had some experience in OO programming, really always 
avoided defines and odd compiler directives in my code before..

  Best Regards!
Stefano B.