On Thu, 2016-02-25 at 14:31 +0100, Torsten Duwe wrote: > On Thu, Feb 25, 2016 at 11:08:54AM +1100, Balbir Singh wrote: > > How about some comments on r2 > > r2 is still pointing to the module's toc, will be saved by ftrace_caller and restored by the instruction following bl ftrace_caller (after patching _mcount/nop) > > To be precise: ftrace_caller needs to save _and_ restore r2 in case of -mprofile-kernel. > > > + /* Stub uses address relative to kernel_toc */ > > > + reladdr = (unsigned long)ftrace_caller - get_paca()->kernel_toc; Yeah true. I originally wrote it with the address of ftrace_caller passed as an argument, so it had to be computed at runtime, and getting it from the paca is ~= to getting it out of the GOT. > kernel_toc is a compile time constant; do you really want to look it up in > memory at runtime each time? It's a bit tricky to get the +- 0x8000 right > OTOH... > > I wrote: > extern unsigned long __toc_start; > reladdr = addr - ((unsigned long)(&__toc_start) + 0x8000UL); > > looks a bit odd, but evaluates to a constant for ftrace_caller. Yeah that makes sense. I'll add a helper to do the + 32k. 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
