On 24/03/16 22:04, Michael Ellerman wrote: > Add the kconfig logic & assembly support for handling live patched > functions. This depends on DYNAMIC_FTRACE_WITH_REGS, which in turn > depends on the new -mprofile-kernel ftrace ABI, which is only supported > currently on ppc64le. > > Live patching is handled by a special ftrace handler. This means it runs > from ftrace_caller(). The live patch handler modifies the NIP so as to > redirect the return from ftrace_caller() to the new patched function. > > However there is one particularly tricky case we need to handle. > > If a function A calls another function B, and it is known at link time > that they share the same TOC, then A will not save or restore its TOC, > and will call the local entry point of B. > > When we live patch B, we replace it with a new function C, which may > not have the same TOC as A. At live patch time it's too late to modify A > to do the TOC save/restore, so the live patching code must interpose > itself between A and C, and do the TOC save/restore that A omitted. > > An additionaly complication is that the livepatch code can not create a > stack frame in order to save the TOC. That is because if C takes > 8 > arguments, or is varargs, A will have written the arguments for C in > A's stack frame. > > To solve this, we introduce a "livepatch stack" which grows upward from > the base of the regular stack, and is used to store the TOC & LR when > calling a live patched function. > > When the patched function returns, we retrieve the real LR & TOC from > the livepatch stack, restore them, and pop the livepatch "stack frame". > > Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > Reviewed-by: Balbir Singh <bsingharora@xxxxxxxxx> -- 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
