On Thu, 2012-08-23 at 21:47 +0530, Srikar Dronamraju wrote: > * Benjamin Herrenschmidt <b...@kernel.crashing.org> [2012-08-23 20:06:18]: > > > On Thu, 2012-08-23 at 11:02 +0530, Srikar Dronamraju wrote: > > > > > > > > > > insn is updated/accessed in the arch independent code. Size of > > > uprobe_opcode_t could be different for different archs. > > > uprobe_opcode_t > > > represents the size of the smallest breakpoint instruction for an > > > arch. > > > > > > Hence u8 works out the best. I know we could still use uprobe_opcode_t > > > and achieve the same. In which case, we would have to interpret > > > MAX_UINSN_BYTES differently. Do you see any advantages of using > > > uprobe_opcode_t instead of u8 across archs? > > > > But don't you actively rely on the fact that on powerpc, unlike x86, you > > -can- atomically replace an instruction with a single 32-bit store ? > > > > We are not doing a replace here, we are only copying from the ->vm_file > for the largest size instruction possible for that instruction. For > powerpc, this is easy because of fixed size instructions. > > On other archs, at this point, we dont even know the length of the > underlying instruction. > > Now there are 3 ways to handle this: > 1. use arch independent copy_insn() (current.) (handles if the > instruction spreads across multiple pages on non fixed instruction > archs). > > 2. make the copy_insn() arch specific, that would mean every arch will > have to do read_mapping_page etc. > > 3. have a arch specific hook in arch independent copy_insn code that > either does a memcpy for non fixed instruction archs or does an > assignment in archs like powerpc. > > I think you are suggesting option 3. > But instead of adding another call that does the arch specific stuff, we > are probably be better of doing a memcpy. Right? > > For all powerpc references to insn we could refer to it as u32 as > suggested by Oleg.
Ok, doens't matter much either way, it's just odd and inefficient. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
