From 85baa095497f3e590df9f6c8932121f123efca5c Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Thu, 24 Mar 2016 22:04:05 +1100 Subject: powerpc/livepatch: Add live patching support on ppc64le 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 Reviewed-by: Torsten Duwe Reviewed-by: Balbir Singh --- arch/powerpc/kernel/asm-offsets.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/powerpc/kernel/asm-offsets.c') diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 07cebc3514f3..723efac2d917 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -86,6 +86,10 @@ int main(void) DEFINE(KSP_LIMIT, offsetof(struct thread_struct, ksp_limit)); #endif /* CONFIG_PPC64 */ +#ifdef CONFIG_LIVEPATCH + DEFINE(TI_livepatch_sp, offsetof(struct thread_info, livepatch_sp)); +#endif + DEFINE(KSP, offsetof(struct thread_struct, ksp)); DEFINE(PT_REGS, offsetof(struct thread_struct, regs)); #ifdef CONFIG_BOOKE -- cgit v1.2.3