Re: Assembly constraints - offset?

[Avi Kivity <avi at qumranet dot com>]

Ian Lance Taylor wrote:
> Avi Kivity <avi@qumranet.com> writes:
>
>   
> > I'd like to access several members of a structure from inline assembly
> > (x86):
> >
> > asm ( "mov $1, %[member1](%[base]) \n\t"
> >           "mov $2, %[member2](%[base]) \n\t"
> >           : : [base]"r"(ptr),
> >               [member1]"i"(offsetof(struct the_struct, member1)),
> >               [member2]"i"(offsetof(struct the_struct, member2)));
> >
> > However, the "i" constraint generates an immediate marker ('$'), so I get
> >
> >     mov $1, $4(%ecx)
> >     mov $2, $8(%ecx)
> >
> > The second '$' is a bit unhelpful.
> >
> > Is there any constraint which will emit the offset without the '$'?
> >     
>
> Using %[member1]c should work.
>   

Where exactly?

In the instruction section ("mov $1, %[member]c(%[base])") the 'c' is 
emitted unchanged.

In the constraint section ([member1]"c"(...)) 'c' means the ecx or rcx 
register.

Thanks,

Avi

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.