On Thu, Nov 29, 2018 at 10:58 AM Linus Torvalds
<[email protected]> wrote:
>
> In contrast, if the call was wrapped in an inline asm, we'd *know* the
> compiler couldn't turn a "call wrapper(%rip)" into anything else.
Actually, I think I have a better model - if the caller is done with inline asm.
What you can do then is basically add a single-byte prefix to the
"call" instruction that does nothing (say, cs override), and then
replace *that* with a 'int3' instruction.
Boom. Done.
Now, the "int3" handler can just update the instruction in-place, but
leave the "int3" in place, and then return to the next instruction
byte (which is just the normal branch instruction without the prefix
byte).
The cross-CPU case continues to work, because the 'int3' remains in
place until after the IPI.
But that would require that we'd mark those call instruction with
Linus
