On Fri, 15 Apr 2016, Alexander Monakov wrote: > On Fri, 15 Apr 2016, Michael Matz wrote: > > Replace first nop with a breakpoint, handle rest of patching in breakpoint > > handler, patch breakpoint insn last, no need to atomically patch multiple > > instructions. > > Alternatively: replace first nop with a short forward branch that jumps over > the rest of the pad, patch rest of the pad, patch the initial forward branch.
I've noticed an issue in my (and probably Michael's) solution: if there's a thread that made it past the first nop, but is still executing the nop pad, it's unsafe to replace the nops. To solve that, it suffices to have a forward branch in place of the first nop to begin with (i.e. have the compiler emit it). But if Szabolcs' two-instruction sequence in the adjacent subthread is sufficient, this is moot. Alexander
