On Thu, Jul 21, 2016 at 12:33:36PM -0400, David Long wrote: > On 07/20/2016 12:09 PM, Marc Zyngier wrote: > >On 08/07/16 17:35, David Long wrote: > >>diff --git a/arch/arm64/include/asm/kprobes.h > >>b/arch/arm64/include/asm/kprobes.h > >>new file mode 100644 > >>index 0000000..79c9511 > >>--- /dev/null > >>+++ b/arch/arm64/include/asm/kprobes.h > >>@@ -0,0 +1,60 @@ > >>+/* > >>+ * arch/arm64/include/asm/kprobes.h > >>+ * > >>+ * Copyright (C) 2013 Linaro Limited > >>+ * > >>+ * This program is free software; you can redistribute it and/or modify > >>+ * it under the terms of the GNU General Public License version 2 as > >>+ * published by the Free Software Foundation. > >>+ * > >>+ * This program is distributed in the hope that it will be useful, > >>+ * but WITHOUT ANY WARRANTY; without even the implied warranty of > >>+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > >>+ * General Public License for more details. > >>+ */ > >>+ > >>+#ifndef _ARM_KPROBES_H > >>+#define _ARM_KPROBES_H > >>+ > >>+#include <linux/types.h> > >>+#include <linux/ptrace.h> > >>+#include <linux/percpu.h> > >>+ > >>+#define __ARCH_WANT_KPROBES_INSN_SLOT > >>+#define MAX_INSN_SIZE 1 > >>+#define MAX_STACK_SIZE 128 > > > >Where is that value coming from? Because even on my 6502, I have a 256 > >byte stack. > > Although I don't claim to know the original author's thoughts I would guess > it is based on the seven other existing implementations for kprobes on > various architectures, all of which appear to use either 64 or 128 for > MAX_STACK_SIZE. The code is not trying to duplicate the whole stack.
This seems to be some random choice in the hope that arguments passed on the stack cannot exceed MAX_STACK_SIZE. I'll put a patch together which checks the previous stack frame and limit the copying. If the fp information or if the size to be copied exceeds MAX_STACK_SIZE, just skip the probe hook (return 0 in setjmp_pre_handler). -- Catalin
