Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx> writes: > On Monday 13 November 2017 02:08 PM, Balbir Singh wrote: >> On Fri, Nov 10, 2017 at 2:28 PM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: >>> On Fri, Nov 10, 2017 at 01:06:25PM +1100, Balbir Singh wrote: >>>> On Fri, Nov 10, 2017 at 2:19 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: >>>>> FWIW, I think it won't matter anyway. I'm currently pursuing the option >>>>> of inserting nops after local calls, because it has less runtime >>>>> complexity than using a stub. >>>>> >>>>> I think I've figured out a way to do it with a GCC plugin, but if that >>>>> doesn't work I'll try the asm listing sed approach suggested by Michael. >>>>> >>>> >>>> A plugin that runs for the new kernel with the patch? Just for >>>> specific files involved in the patch? >>> >>> The plugin will affect the code generation of all functions in the patch >>> module. So all calls in all replacement functions will have the nops. >>> >>> Here's a prototype (not yet fully tested): >>> >>> https://github.com/jpoimboe/kpatch/blob/TODO-ppc-fix/kpatch-build/gcc-plugins/ppc64le-plugin.c >>> >> > > [...] > >> I'd have to look closer, but I wonder what happens if a >> function has no global entry >> point >> >> (See http://mpe.github.io/posts/2016/05/23/kernel-live-patching-for-ppc64le/) >> section >> Understanding the TOC & entry points and the example of int_to_scsilun() >> > > int_to_scsilun() is accessed via global entry point, but the TOC setup > part in the function prologue is skipped as the function doesn't have a > need to save/restore TOC. The reason begin, it doesn't calls any global > functions, thus the r2 register is not clobbered. > > As per my understanding, the plug-in inserts a nop instruction after > branch to a function called via localentry a.k.a call to local > function. In case of int_to_scsilun(), the plug-in will not modify the > function in any way, as there are no local calls also made by the > int_to_scsilun(). Yeah there should be no issue. This happens all the time, ie. the compiler sees it needs to make a global call, inserts the nop, but then it turns out the callee didn't need to use the TOC anyway. cheers -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
