On Tue, Jul 08, 2014 at 10:07:40AM +0200, Heiko Carstens wrote: > On Thu, Jul 03, 2014 at 02:00:46PM +0200, Vojtech Pavlik wrote: > > Add support for DYNAMIC_FTRACE_WITH_REGS to 64-bit and 31-bit s390 > > architectures. This is required for kGraft and kpatch to work on s390. > > > > It's done by adding a _regs variant of ftrace_caller that preserves > > registers and puts them on stack in a struct pt_regs layout and > > allows modification of return address by changing the PSW (instruction > > pointer) member od struct pt_regs. > > > > Signed-off-by: Vojtech Pavlik <vojtech@xxxxxxx> > > Reviewed-by: Jiri Kosina <jkosina@xxxxxxx> > > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > > So I assume you use the instruction_pointer() macro to access the > return address then? > > All of this seems a bit of a hack to me.. the natural place of the > return address of a function would be register 14, and not the > psw member of the pt_regs structure. > > It's then also inconsistent to only save register r0-r13 to the > gprs member.. well, you can't save r14, since what should > happen if both r14 in the gprs member of pt_regs and in the psw > part would have been changed? > > Besides that a couple more comments below. [...] > Some objections: this code assumes that sizeof(struct pt_regs) does not > change, which is not correct. So as soon as we touch struct pt_regs this > code would be broken. Also the order of the members within struct pt_regs > is not necessarily static (pt_regs is not ABI). FWIW, this already happened with d3a73acbc26a4a81a01a35fd162973e53d0386f5 "s390: split TIF bits into CIF, PIF and TIF bits". Anyway, since I didn't got any response from you during the last couple of weeks, I changed the ftrace code so it should fit your needs. I will send five patches in reply to this mail - patch 4 of 5 is the one that implements the DYNAMIC_FTRACE_WITH_REGS functionality, how differently to your patch, especially possible return address changing. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
