On 03/31/2014 05:44 AM, dw wrote:
> So, after looking over this discussion, I have updated the text. This
> time no undefined terms, while still conveying all the points I had in mind:
>
> The "memory" clobber tells the compiler that the assembly code performs
> memory reads or writes to items other than those listed in the input and
> output operands (for example accessing the memory pointed to by one of
> the input parameters). To ensure memory contains correct values, GCC
> may need to flush specific register values to memory before executing
> the asm. Further, the compiler will not assume that any values read from
> memory before the @code{asm} will remain unchanged after the @code{asm};
> it will reload them as needed. This effectively forms a read/write
> memory barrier for the compiler.
>
> Note that this clobber does not prevent the @emph{processor} from doing
> speculative reads past the @code{asm} statement. To stop that, you need
> processor-specific fence instructions.
>
> Objections?
No, none. That's fine.
Andrew.
