Messages in this thread | | | Date | Thu, 10 Jan 2019 14:52:26 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH v3 0/6] Static calls |
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On Thu, Jan 10, 2019 at 09:30:23PM +0100, Peter Zijlstra wrote: > On Wed, Jan 09, 2019 at 04:59:35PM -0600, Josh Poimboeuf wrote: > > With this version, I stopped trying to use text_poke_bp(), and instead > > went with a different approach: if the call site destination doesn't > > cross a cacheline boundary, just do an atomic write. Otherwise, keep > > using the trampoline indefinitely. > > > - Get rid of the use of text_poke_bp(), in favor of atomic writes. > > Out-of-line calls will be promoted to inline only if the call sites > > don't cross cache line boundaries. [Linus/Andy] > > Can we perserve why text_poke_bp() didn't work? I seem to have forgotten > again. The problem was poking the return address onto the stack from the > int3 handler, or something along those lines?
Right, emulating a call instruction from the #BP handler is ugly, because you have to somehow grow the stack to make room for the return address. Personally I liked the idea of shifting the iret frame by 16 bytes in the #DB entry code, but others hated it.
So many bad-but-not-completely-unacceptable options to choose from.
-- Josh
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