[RFC PATCH v2 1/3] arch/powerpc : Add detour buffer support for optprobes

[Anju T]

Detour buffer contains instructions to create an in memory pt_regs.
After the execution of prehandler a call is made for instruction emulation.
The NIP is decided after the probed instruction is executed. Hence a branch
instruction is created to the NIP returned by emulate_step().

Instruction slot for detour buffer is allocated from
the reserved area. For the time being 64KB is reserved
in memory for this purpose.

Signed-off-by: Anju T <anju@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/kprobes.h   |  25 ++++++++
 arch/powerpc/kernel/optprobes_head.S | 108 +++++++++++++++++++++++++++++++++++
 2 files changed, 133 insertions(+)
 create mode 100644 arch/powerpc/kernel/optprobes_head.S

diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index 039b583..3e4c998 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -38,7 +38,25 @@ struct pt_regs;
 struct kprobe;
 
 typedef ppc_opcode_t kprobe_opcode_t;
+
+extern kprobe_opcode_t optinsn_slot;
+/* Optinsn template address */
+extern kprobe_opcode_t optprobe_template_entry[];
+extern kprobe_opcode_t optprobe_template_call_handler[];
+extern kprobe_opcode_t optprobe_template_call_emulate[];
+extern kprobe_opcode_t optprobe_template_ret_branch[];
+extern kprobe_opcode_t optprobe_template_ret[];
+extern kprobe_opcode_t optprobe_template_insn[];
+extern kprobe_opcode_t optprobe_template_op_address1[];
+extern kprobe_opcode_t optprobe_template_op_address2[];
+extern kprobe_opcode_t optprobe_template_end[];
+
 #define MAX_INSN_SIZE 1
+#define MAX_OPTIMIZED_LENGTH    4
+#define MAX_OPTINSN_SIZE				\
+	((unsigned long)&optprobe_template_end -	\
+	(unsigned long)&optprobe_template_entry)
+#define RELATIVEJUMP_SIZE       4
 
 #ifdef CONFIG_PPC64
 #if defined(_CALL_ELF) && _CALL_ELF == 2
@@ -129,5 +147,12 @@ struct kprobe_ctlblk {
 extern int kprobe_exceptions_notify(struct notifier_block *self,
 					unsigned long val, void *data);
 extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
+
+struct arch_optimized_insn {
+	kprobe_opcode_t copied_insn[1];
+	/* detour buffer */
+	kprobe_opcode_t *insn;
+};
+
 #endif /* __KERNEL__ */
 #endif	/* _ASM_POWERPC_KPROBES_H */
diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.S
new file mode 100644
index 0000000..ce32aec
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes_head.S
@@ -0,0 +1,108 @@
+/*
+ * Code to prepare detour buffer for optprobes in kernel.
+ *
+ * Copyright 2016, Anju T, IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <asm/ppc_asm.h>
+#include <asm/ptrace.h>
+#include <asm/asm-offsets.h>
+
+.global optinsn_slot
+optinsn_slot:
+	/* Reserve an area to allocate slots for detour buffer */
+	.space	65536
+.global optprobe_template_entry
+optprobe_template_entry:
+	stdu	r1,-INT_FRAME_SIZE(r1)
+	SAVE_GPR(0,r1)
+	/* Save the previous SP into stack */
+	addi	r0,r1,INT_FRAME_SIZE
+	std	0,GPR1(r1)
+	SAVE_2GPRS(2,r1)
+	SAVE_8GPRS(4,r1)
+	SAVE_10GPRS(12,r1)
+	SAVE_10GPRS(22,r1)
+	/* Save SPRS */
+	mfcfar	r5
+	std	r5,_NIP(r1)
+	mfmsr	r5
+	std	r5,_MSR(r1)
+	mfctr	r5
+	std	r5,_CTR(r1)
+	mflr	r5
+	std	r5,_LINK(r1)
+	mfspr	r5,SPRN_XER
+	std	r5,_XER(r1)
+	li	r5,0
+	std	r5,_TRAP(r1)
+	mfdar	r5
+	std	r5,_DAR(r1)
+	mfdsisr	r5
+	std	r5,_DSISR(r1)
+	/* Pass parameters for optimized_callback */
+.global optprobe_template_op_address1
+optprobe_template_op_address1:
+	nop
+	nop
+	nop
+	nop
+	nop
+	addi	r4,r1,STACK_FRAME_OVERHEAD
+	/* Branch to the prehandler */
+.global optprobe_template_call_handler
+optprobe_template_call_handler:
+	nop
+	/* Pass parameters for instruction emulation */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+.global optprobe_template_insn
+optprobe_template_insn:
+	nop
+	nop
+	/* Branch to instruction emulation  */
+.global optprobe_template_call_emulate
+optprobe_template_call_emulate:
+	nop
+.global optprobe_template_op_address2
+optprobe_template_op_address2:
+	nop
+	nop
+	nop
+	nop
+	nop
+	addi	r4,r1,STACK_FRAME_OVERHEAD
+	/* Branch to create_return_branch() function */
+.global optprobe_template_ret_branch
+optprobe_template_ret_branch:
+	nop
+	/* Restore the registers */
+	ld	r5,_MSR(r1)
+	mtmsr	r5
+	ld	r5,_CTR(r1)
+	mtctr	r5
+	ld	r5,_LINK(r1)
+	mtlr	r5
+	ld	r5,_XER(r1)
+	mtxer	r5
+	ld	r5,_DAR(r1)
+	mtdar	r5
+	ld	r5,_DSISR(r1)
+	mtdsisr	r5
+	REST_GPR(0,r1)
+	REST_2GPRS(2,r1)
+	REST_8GPRS(4,r1)
+	REST_10GPRS(12,r1)
+	REST_10GPRS(22,r1)
+	/* Restore the previous SP */
+	addi	r1,r1,INT_FRAME_SIZE
+	/* Jump back to the normal workflow from trampoline */
+.global optprobe_template_ret
+optprobe_template_ret:
+	nop
+.global optprobe_template_end
+optprobe_template_end:
-- 
2.1.0