Re: GCC proposal for "@" asm constraint

[Jamie Lokier <egcs at tantalophile dot demon dot co dot uk>]

Andrea Arcangeli wrote:
> > p is a variable.  The _address_ of p is constant, but the reload is
> > not loading the address of p, it's loading the _value_.  That value can
> 
> Wrong: it's really loading the _address_. The value that is loaded into the
> register is the addess of p that is stored only in the .text and that is an
> immediate value embedded into the opcodes of the asm.
> 
> If you can change the address it it means it's selfmodifying code, and GCC
> shouldn't really assume anything about that so GCC is _wrong_.
> 
...
>  80483f5:       a1 a4 95 04 08          mov    0x80495a4,%eax

That instruction loads the _value_ of p.  I.e. reads the memory from
location 0x80495a4 into %eax.  The source instruction was:

       movl p,%eax

The instructions that you're thinking of, that load fixed addresses,
look like these:

       mov $0x80495a4,%eax
       lea 0x80495a4,%eax

or in source form:

       movl $p,%eax
       leal p,%eax

You must be working too hard.
Please take a short break, relax, enjoy nature again :-)

have a nice day,
-- Jamie