"Lin Chun-Zhi" <lcz90@xxxxxxxxxxxxx> writes:
> I got a question about register constraint in kernel source.
> Here is the cut of bios32_service()
>
> 597 __asm__("lcall (%%edi); cld"
> 598 : "=a" (return_code),
> 599 "=b" (address),
> 600 "=c" (length),
> 601 "=d" (entry)
> 602 : "" (service),
> 603 "1" (0),
> 604 "D" (&bios32_indirect));
>
> In line 602, its register constraint is a NULL string. I can't find how
> compiler arranges the registers in gcc.info.
If there are no constraints, the compiler does not constrain the
operand. It could be anywhere. The statement will use "service",
though; assignments to it will not be deleted.
By the way, in linux-2.6.8.1 that statement looks like this:
__asm__("lcall *(%%edi); cld"
: "=a" (return_code),
"=b" (address),
"=c" (length),
"=d" (entry)
: "0" (service),
"1" (0),
"D" (&bios32_indirect));
Ian
