On Thu, 29 Nov 2018 11:08:26 -0800 Linus Torvalds <torva...@linux-foundation.org> wrote:
> On Thu, Nov 29, 2018 at 10:58 AM Linus Torvalds > <torva...@linux-foundation.org> 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 > In my original proof of concept, I tried to to implement the callers with asm, but then the way to handle parameters became a nightmare. The goal of this (for me) was to replace the tracepoint indirect calls with static calls, and tracepoints can have any number of parameters to pass. I ended up needing the compiler to help me with the passing of parameters. -- Steve
