Subject: Re: [PATCH V2 3/4] arch/powerpc: Implement Optprobes
To: Masami Hiramatsu <mhiramat@kernel.org>
References: <1481732310-7779-1-git-send-email-anju@linux.vnet.ibm.com>
 <1481732310-7779-2-git-send-email-anju@linux.vnet.ibm.com>
 <20161216230256.89472387164de66c3a6888f5@kernel.org>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        ananth@in.ibm.com, naveen.n.rao@linux.vnet.ibm.com, paulus@samba.org,
        srikar@linux.vnet.ibm.com, benh@kernel.crashing.org,
        mpe@ellerman.id.au, mahesh@linux.vnet.ibm.com
From: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Date: Fri, 16 Dec 2016 23:24:54 +0530
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Hi Masami,


On Friday 16 December 2016 07:32 PM, Masami Hiramatsu wrote:
> On Wed, 14 Dec 2016 21:48:27 +0530
> Anju T Sudhakar <anju@linux.vnet.ibm.com> wrote:
>
>> Detour buffer contains instructions to create an in memory pt_regs.
>> After the execution of the pre-handler, a call is made for instruction emulation.
>> The NIP is determined in advanced through dummy instruction emulation and a branch
>> instruction is created to the NIP at the end of the trampoline.
>>
>> Instruction slot for detour buffer is allocated from the reserved area.
>> For the time being, 64KB is reserved in memory for this purpose.
>>
>> Instructions which can be emulated using analyse_instr() are suppliants
>> for optimization. Before optimization ensure that the address range
>> between the detour buffer allocated and the instruction being probed
>> is within ± 32MB.
> Thank you for updating!
> I think this has no critical issue, but I have some comments on it.
> (just cleanup and hardenings)
> Please see below.
>
>> Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
>> Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>> ---
>>   .../features/debug/optprobes/arch-support.txt      |   2 +-
>>   arch/powerpc/Kconfig                               |   1 +
>>   arch/powerpc/include/asm/kprobes.h                 |  23 +-
>>   arch/powerpc/include/asm/sstep.h                   |   1 +
>>   arch/powerpc/kernel/Makefile                       |   1 +
>>   arch/powerpc/kernel/optprobes.c                    | 333 +++++++++++++++++++++
>>   arch/powerpc/kernel/optprobes_head.S               | 135 +++++++++
>>   arch/powerpc/lib/sstep.c                           |  22 ++
>>   8 files changed, 516 insertions(+), 2 deletions(-)
>>   create mode 100644 arch/powerpc/kernel/optprobes.c
>>   create mode 100644 arch/powerpc/kernel/optprobes_head.S
>>
>> diff --git a/Documentation/features/debug/optprobes/arch-support.txt b/Documentation/features/debug/optprobes/arch-support.txt
>> index b8999d8..45bc99d 100644
>> --- a/Documentation/features/debug/optprobes/arch-support.txt
>> +++ b/Documentation/features/debug/optprobes/arch-support.txt
>> @@ -27,7 +27,7 @@
>>       |       nios2: | TODO |
>>       |    openrisc: | TODO |
>>       |      parisc: | TODO |
>> -    |     powerpc: | TODO |
>> +    |     powerpc: |  ok  |
>>       |        s390: | TODO |
>>       |       score: | TODO |
>>       |          sh: | TODO |
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index c7f120a..d563f0a 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -98,6 +98,7 @@ config PPC
>>   	select HAVE_IOREMAP_PROT
>>   	select HAVE_EFFICIENT_UNALIGNED_ACCESS if !(CPU_LITTLE_ENDIAN && POWER7_CPU)
>>   	select HAVE_KPROBES
>> +	select HAVE_OPTPROBES if PPC64
>>   	select HAVE_ARCH_KGDB
>>   	select HAVE_KRETPROBES
>>   	select HAVE_ARCH_TRACEHOOK
>> diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
>> index 2c9759bd..739ddc5 100644
>> --- a/arch/powerpc/include/asm/kprobes.h
>> +++ b/arch/powerpc/include/asm/kprobes.h
>> @@ -38,7 +38,22 @@ struct pt_regs;
>>   struct kprobe;
>>   
>>   typedef ppc_opcode_t kprobe_opcode_t;
>> -#define MAX_INSN_SIZE 1
>> +
>> +extern kprobe_opcode_t optinsn_slot;
>> +
>> +/* Optinsn template address */
>> +extern kprobe_opcode_t optprobe_template_entry[];
>> +extern kprobe_opcode_t optprobe_template_op_address[];
>> +extern kprobe_opcode_t optprobe_template_call_handler[];
>> +extern kprobe_opcode_t optprobe_template_insn[];
>> +extern kprobe_opcode_t optprobe_template_call_emulate[];
>> +extern kprobe_opcode_t optprobe_template_ret[];
>> +extern kprobe_opcode_t optprobe_template_end[];
>> +
>> +#define MAX_INSN_SIZE		1
>> +#define MAX_OPTIMIZED_LENGTH	4
>> +#define MAX_OPTINSN_SIZE	(optprobe_template_end - optprobe_template_entry)
>> +#define RELATIVEJUMP_SIZE	4
> These size/length macros seems a bit odd. I guess MAX_INSN_SIZE
> is based on sizeof(MAX_INSN_SIZE), but others are in byte.
> Could you fix that? For example, define it with
> sizeof(kprobe_opcode_t), and add comments on it, etc.

Sure. I will look into this and define it in  a consistent way.

>>   
>>   #ifdef PPC64_ELF_ABI_v2
>>   /* PPC64 ABIv2 needs local entry point */
>> @@ -124,6 +139,12 @@ struct kprobe_ctlblk {
>>   	struct prev_kprobe prev_kprobe;
>>   };
>>   
>> +struct arch_optimized_insn {
>> +	kprobe_opcode_t copied_insn[1];
>> +	/* detour buffer */
>> +	kprobe_opcode_t *insn;
>> +};
>> +
>>   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);
>> diff --git a/arch/powerpc/include/asm/sstep.h b/arch/powerpc/include/asm/sstep.h
>> index d3a42cc..f7ad425 100644
>> --- a/arch/powerpc/include/asm/sstep.h
>> +++ b/arch/powerpc/include/asm/sstep.h
>> @@ -87,3 +87,4 @@ struct instruction_op {
>>   
>>   extern int analyse_instr(struct instruction_op *op, struct pt_regs *regs,
>>   			 unsigned int instr);
>> +extern bool is_conditional_branch(unsigned int instr);
>> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
>> index 1925341..54f0f47 100644
>> --- a/arch/powerpc/kernel/Makefile
>> +++ b/arch/powerpc/kernel/Makefile
>> @@ -98,6 +98,7 @@ obj-$(CONFIG_KGDB)		+= kgdb.o
>>   obj-$(CONFIG_BOOTX_TEXT)	+= btext.o
>>   obj-$(CONFIG_SMP)		+= smp.o
>>   obj-$(CONFIG_KPROBES)		+= kprobes.o
>> +obj-$(CONFIG_OPTPROBES)		+= optprobes.o optprobes_head.o
>>   obj-$(CONFIG_UPROBES)		+= uprobes.o
>>   obj-$(CONFIG_PPC_UDBG_16550)	+= legacy_serial.o udbg_16550.o
>>   obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
>> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
>> new file mode 100644
>> index 0000000..ecba221
>> --- /dev/null
>> +++ b/arch/powerpc/kernel/optprobes.c
>> @@ -0,0 +1,333 @@
>> +/*
>> + * Code for Kernel probes Jump optimization.
>> + *
>> + * 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 <linux/kprobes.h>
>> +#include <linux/jump_label.h>
>> +#include <linux/types.h>
>> +#include <linux/slab.h>
>> +#include <linux/list.h>
>> +#include <asm/kprobes.h>
>> +#include <asm/ptrace.h>
>> +#include <asm/cacheflush.h>
>> +#include <asm/code-patching.h>
>> +#include <asm/sstep.h>
>> +#include <asm/ppc-opcode.h>
>> +
>> +#define TMPL_CALL_HDLR_IDX	\
>> +	(optprobe_template_call_handler - optprobe_template_entry)
>> +#define TMPL_EMULATE_IDX	\
>> +	(optprobe_template_call_emulate - optprobe_template_entry)
>> +#define TMPL_RET_IDX		\
>> +	(optprobe_template_ret - optprobe_template_entry)
>> +#define TMPL_OP_IDX		\
>> +	(optprobe_template_op_address - optprobe_template_entry)
>> +#define TMPL_INSN_IDX		\
>> +	(optprobe_template_insn - optprobe_template_entry)
>> +#define TMPL_END_IDX		\
>> +	(optprobe_template_end - optprobe_template_entry)
>> +
>> +DEFINE_INSN_CACHE_OPS(ppc_optinsn);
>> +
>> +static bool insn_page_in_use;
>> +
>> +static void *__ppc_alloc_insn_page(void)
>> +{
>> +	if (insn_page_in_use)
>> +		return NULL;
>> +	insn_page_in_use = true;
>> +	return &optinsn_slot;
>> +}
>> +
>> +static void __ppc_free_insn_page(void *page __maybe_unused)
>> +{
>> +	insn_page_in_use = false;
>> +}
>> +
>> +struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
>> +	.mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
>> +	.pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
>> +	/* insn_size initialized later */
>> +	.alloc = __ppc_alloc_insn_page,
>> +	.free = __ppc_free_insn_page,
>> +	.nr_garbage = 0,
>> +};
>> +
>> +/*
>> + * Check if we can optimize this probe. Returns NIP post-emulation if this can
>> + * be optimized and 0 otherwise.
>> + */
>> +static unsigned long can_optimize(struct kprobe *p)
>> +{
>> +	struct pt_regs regs;
>> +	struct instruction_op op;
>> +	unsigned long nip = 0;
>> +
>> +	/*
>> +	 * kprobe placed for kretprobe during boot time
>> +	 * is not optimizing now.
>> +	 *
>> +	 * TODO: Optimize kprobe in kretprobe_trampoline
>> +	 */
>> +	if (p->addr == (kprobe_opcode_t *)&kretprobe_trampoline)
>> +		return 0;
>> +
>> +	/*
>> +	 * We only support optimizing kernel addresses, but not
>> +	 * module addresses.
>> +	 */
>> +	if (!is_kernel_addr((unsigned long)p->addr))
>> +		return 0;
>> +
>> +	regs.nip = (unsigned long)p->addr;
>> +	regs.trap = 0x0;
>> +	regs.msr = MSR_KERNEL;
>> +
>> +	/*
>> +	 * Ensure that the instruction is not a conditional branch,
>> +	 * and that can be emulated.
>> +	 */
>> +	if (!is_conditional_branch(*p->ainsn.insn) &&
>> +			analyse_instr(&op, &regs, *p->ainsn.insn))
>> +		nip = regs.nip;
>> +
>> +	return nip;
>> +}
>> +
>> +static void optimized_callback(struct optimized_kprobe *op,
>> +			       struct pt_regs *regs)
>> +{
>> +	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
>> +	unsigned long flags;
>> +
>> +	/* This is possible if op is under delayed unoptimizing */
>> +	if (kprobe_disabled(&op->kp))
>> +		return;
>> +
>> +	local_irq_save(flags);
>> +
>> +	if (kprobe_running()) {
>> +		kprobes_inc_nmissed_count(&op->kp);
>> +	} else {
>> +		__this_cpu_write(current_kprobe, &op->kp);
>> +		regs->nip = (unsigned long)op->kp.addr;
>> +		kcb->kprobe_status = KPROBE_HIT_ACTIVE;
>> +		opt_pre_handler(&op->kp, regs);
>> +		__this_cpu_write(current_kprobe, NULL);
>> +	}
>> +	local_irq_restore(flags);
>> +}
>> +NOKPROBE_SYMBOL(optimized_callback);
>> +
>> +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
>> +{
>> +	if (op->optinsn.insn) {
>> +		free_ppc_optinsn_slot(op->optinsn.insn, 1);
>> +		op->optinsn.insn = NULL;
>> +	}
>> +}
>> +
>> +/*
>> + * emulate_step() requires insn to be emulated as
>> + * second parameter. Load register 'r4' with the
>> + * instruction.
>> + */
>> +void patch_imm32_load_insns(unsigned int val, kprobe_opcode_t *addr)
>> +{
>> +	/* addis r4,0,(insn)@h */
>> +	*addr++ = PPC_INST_ADDIS | ___PPC_RT(4) |
>> +		  ((val >> 16) & 0xffff);
>> +
>> +	/* ori r4,r4,(insn)@l */
>> +	*addr = PPC_INST_ORI | ___PPC_RA(4) | ___PPC_RS(4) |
>> +		(val & 0xffff);
>> +}
>> +
>> +/*
>> + * Generate instructions to load provided immediate 64-bit value
>> + * to register 'r3' and patch these instructions at 'addr'.
>> + */
>> +void patch_imm64_load_insns(unsigned long val, kprobe_opcode_t *addr)
>> +{
>> +	/* lis r3,(op)@highest */
>> +	*addr++ = PPC_INST_ADDIS | ___PPC_RT(3) |
>> +		  ((val >> 48) & 0xffff);
>> +
>> +	/* ori r3,r3,(op)@higher */
>> +	*addr++ = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
>> +		  ((val >> 32) & 0xffff);
>> +
>> +	/* rldicr r3,r3,32,31 */
>> +	*addr++ = PPC_INST_RLDICR | ___PPC_RA(3) | ___PPC_RS(3) |
>> +		  __PPC_SH64(32) | __PPC_ME64(31);
>> +
>> +	/* oris r3,r3,(op)@h */
>> +	*addr++ = PPC_INST_ORIS | ___PPC_RA(3) | ___PPC_RS(3) |
>> +		  ((val >> 16) & 0xffff);
>> +
>> +	/* ori r3,r3,(op)@l */
>> +	*addr = PPC_INST_ORI | ___PPC_RA(3) | ___PPC_RS(3) |
>> +		(val & 0xffff);
>> +}
> I need another PPC maintainer review for these.

ok.
>> +
>> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
>> +{
>> +	kprobe_opcode_t *buff, branch_op_callback, branch_emulate_step;
>> +	kprobe_opcode_t *op_callback_addr, *emulate_step_addr;
>> +	long b_offset;
>> +	unsigned long nip;
>> +
>> +	kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
>> +
>> +	nip = can_optimize(p);
>> +	if (!nip)
>> +		return -EILSEQ;
>> +
>> +	/* Allocate instruction slot for detour buffer */
>> +	buff = get_ppc_optinsn_slot();
>> +	if (!buff)
>> +		return -ENOMEM;
>> +
>> +	/*
>> +	 * OPTPROBE uses 'b' instruction to branch to optinsn.insn.
>> +	 *
>> +	 * The target address has to be relatively nearby, to permit use
>> +	 * of branch instruction in powerpc, because the address is specified
>> +	 * in an immediate field in the instruction opcode itself, ie 24 bits
>> +	 * in the opcode specify the address. Therefore the address should
>> +	 * be within 32MB on either side of the current instruction.
>> +	 */
>> +	b_offset = (unsigned long)buff - (unsigned long)p->addr;
>> +	if (!is_offset_in_branch_range(b_offset)) {
>> +		free_ppc_optinsn_slot(buff, 0);
>> +		return -ERANGE;
>> +	}
>> +
>> +	/* Check if the return address is also within 32MB range */
>> +	b_offset = (unsigned long)(buff + TMPL_RET_IDX) -
>> +			(unsigned long)nip;
>> +	if (!is_offset_in_branch_range(b_offset)) {
>> +		free_ppc_optinsn_slot(buff, 0);
>> +		return -ERANGE;
>> +	}
>> +
>> +	/* Setup template */
>> +	memcpy(buff, optprobe_template_entry,
>> +			TMPL_END_IDX * sizeof(kprobe_opcode_t));
>> +
>> +	/*
>> +	 * Fixup the template with instructions to:
>> +	 * 1. load the address of the actual probepoint
>> +	 */
>> +	patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
>> +
>> +	/*
>> +	 * 2. branch to optimized_callback() and emulate_step()
>> +	 */
>> +	kprobe_lookup_name("optimized_callback", op_callback_addr);
>> +	kprobe_lookup_name("emulate_step", emulate_step_addr);
>> +	if (!op_callback_addr || !emulate_step_addr) {
>> +		free_ppc_optinsn_slot(buff, 0);
>> +		WARN(1, "kprobe_lookup_name() failed\n");
>> +		return -ENOENT;
>> +	}
>> +
>> +	branch_op_callback = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
>> +				(unsigned long)op_callback_addr,
>> +				BRANCH_SET_LINK);
>> +
>> +	branch_emulate_step = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
>> +				(unsigned long)emulate_step_addr,
>> +				BRANCH_SET_LINK);
>> +
>> +	if (!branch_op_callback || !branch_emulate_step) {
>> +		free_ppc_optinsn_slot(buff, 0);
>> +		return -ERANGE;
> Since there are 4 free_ppc_optinsn_slot(buff, 0) and return error pattarns,
> I recommend you to consolidate it by using "goto error".

Ah, nice suggestion. Will change this. Thanks!
>> +	}
>> +
>> +	buff[TMPL_CALL_HDLR_IDX] = branch_op_callback;
>> +	buff[TMPL_EMULATE_IDX] = branch_emulate_step;
>> +
>> +	/*
>> +	 * 3. load instruction to be emulated into relevant register, and
>> +	 */
>> +	patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
>> +
>> +	/*
>> +	 * 4. branch back from trampoline
>> +	 */
>> +	buff[TMPL_RET_IDX] = create_branch((unsigned int *)buff + TMPL_RET_IDX,
>> +				(unsigned long)nip, 0);
>> +
>> +	flush_icache_range((unsigned long)buff,
>> +			   (unsigned long)(&buff[TMPL_END_IDX]));
>> +
>> +	op->optinsn.insn = buff;
>> +
>> +	return 0;
>> +}
>> +
>> +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
>> +{
>> +	return optinsn->insn != NULL;
>> +}
>> +
>> +/*
>> + * On powerpc, Optprobes always replaces one instruction (4 bytes
>> + * aligned and 4 bytes long). It is impossible to encounter another
>> + * kprobe in this address range. So always return 0.
>> + */
>> +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
>> +{
>> +	return 0;
>> +}
>> +
>> +void arch_optimize_kprobes(struct list_head *oplist)
>> +{
>> +	struct optimized_kprobe *op;
>> +	struct optimized_kprobe *tmp;
>> +
>> +	list_for_each_entry_safe(op, tmp, oplist, list) {
>> +		/*
>> +		 * Backup instructions which will be replaced
>> +		 * by jump address
>> +		 */
>> +		memcpy(op->optinsn.copied_insn, op->kp.addr,
>> +					       RELATIVEJUMP_SIZE);
>> +		patch_instruction(op->kp.addr,
>> +			create_branch((unsigned int *)op->kp.addr,
>> +				      (unsigned long)op->optinsn.insn, 0));
> Would you be sure that create_branch doesn't fail?


The b_offset check we did, before optimizing the kprobe will guarantee 
that the branch will be in +/- 32MB range. So create_branch will not fail.


>
>> +		list_del_init(&op->list);
>> +	}
>> +}
>> +
>> +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
>> +{
>> +	arch_arm_kprobe(&op->kp);
>> +}
>> +
>> +void arch_unoptimize_kprobes(struct list_head *oplist,
>> +			     struct list_head *done_list)
>> +{
>> +	struct optimized_kprobe *op;
>> +	struct optimized_kprobe *tmp;
>> +
>> +	list_for_each_entry_safe(op, tmp, oplist, list) {
>> +		arch_unoptimize_kprobe(op);
>> +		list_move(&op->list, done_list);
>> +	}
>> +}
>> +
>> +int arch_within_optimized_kprobe(struct optimized_kprobe *op,
>> +				 unsigned long addr)
>> +{
>> +	return ((unsigned long)op->kp.addr <= addr &&
>> +		(unsigned long)op->kp.addr + RELATIVEJUMP_SIZE > addr);
>> +}
>> diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.S
>> new file mode 100644
>> index 0000000..c86976b
>> --- /dev/null
>> +++ b/arch/powerpc/kernel/optprobes_head.S
>> @@ -0,0 +1,135 @@
>> +/*
>> + * 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>
>> +
>> +#define	OPT_SLOT_SIZE	65536
>> +
>> +	.balign	4
>> +
>> +	/*
>> +	 * Reserve an area to allocate slots for detour buffer.
>> +	 * This is part of .text section (rather than vmalloc area)
>> +	 * as this needs to be within 32MB of the probed address.
>> +	 */
>> +	.global optinsn_slot
>> +optinsn_slot:
>> +	.space	OPT_SLOT_SIZE
>> +
>> +	/*
>> +	 * Optprobe template:
>> +	 * This template gets copied into one of the slots in optinsn_slot
>> +	 * and gets fixed up with real optprobe structures et al.
>> +	 */
>> +	.global optprobe_template_entry
>> +optprobe_template_entry:
>> +	/* Create an in-memory pt_regs */
>> +	stdu	r1,-INT_FRAME_SIZE(r1)
>> +	SAVE_GPR(0,r1)
>> +	/* Save the previous SP into stack */
>> +	addi	r0,r1,INT_FRAME_SIZE
>> +	std	r0,GPR1(r1)
>> +	SAVE_10GPRS(2,r1)
>> +	SAVE_10GPRS(12,r1)
>> +	SAVE_10GPRS(22,r1)
>> +	/* Save SPRS */
>> +	mfmsr	r5
>> +	std	r5,_MSR(r1)
>> +	li	r5,0x700
>> +	std	r5,_TRAP(r1)
>> +	li	r5,0
>> +	std	r5,ORIG_GPR3(r1)
>> +	std	r5,RESULT(r1)
>> +	mfctr	r5
>> +	std	r5,_CTR(r1)
>> +	mflr	r5
>> +	std	r5,_LINK(r1)
>> +	mfspr	r5,SPRN_XER
>> +	std	r5,_XER(r1)
>> +	mfcr	r5
>> +	std	r5,_CCR(r1)
>> +	lbz     r5,PACASOFTIRQEN(r13)
>> +	std     r5,SOFTE(r1)
>> +	mfdar	r5
>> +	std	r5,_DAR(r1)
>> +	mfdsisr	r5
>> +	std	r5,_DSISR(r1)
>> +
>> +	.global optprobe_template_op_address
>> +optprobe_template_op_address:
>> +	/*
>> +	 * Parameters to optimized_callback():
>> +	 * 1. optimized_kprobe structure in r3
>> +	 */
>> +	nop
>> +	nop
>> +	nop
>> +	nop
>> +	nop
>> +	/* 2. pt_regs pointer in r4 */
>> +	addi	r4,r1,STACK_FRAME_OVERHEAD
>> +
>> +	.global optprobe_template_call_handler
>> +optprobe_template_call_handler:
>> +	/* Branch to optimized_callback() */
>> +	nop
>> +
>> +	/*
>> +	 * Parameters for instruction emulation:
>> +	 * 1. Pass SP in register r3.
>> +	 */
>> +	addi	r3,r1,STACK_FRAME_OVERHEAD
>> +
>> +	.global optprobe_template_insn
>> +optprobe_template_insn:
>> +	/* 2, Pass instruction to be emulated in r4 */
>> +	nop
>> +	nop
>> +
>> +	.global optprobe_template_call_emulate
>> +optprobe_template_call_emulate:
>> +	/* Branch to emulate_step()  */
>> +	nop
>> +
>> +	/*
>> +	 * All done.
>> +	 * Now, 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,_CCR(r1)
>> +	mtcr	r5
>> +	ld	r5,_DAR(r1)
>> +	mtdar	r5
>> +	ld	r5,_DSISR(r1)
>> +	mtdsisr	r5
>> +	REST_GPR(0,r1)
>> +	REST_10GPRS(2,r1)
>> +	REST_10GPRS(12,r1)
>> +	REST_10GPRS(22,r1)
>> +	/* Restore the previous SP */
>> +	addi	r1,r1,INT_FRAME_SIZE
>> +
>> +	.global optprobe_template_ret
>> +optprobe_template_ret:
>> +	/* ... and jump back from trampoline */
>> +	nop
>> +
>> +	.global optprobe_template_end
>> +optprobe_template_end:
>> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
>> index 3362299..0c6c2b0 100644
>> --- a/arch/powerpc/lib/sstep.c
>> +++ b/arch/powerpc/lib/sstep.c
>> @@ -618,6 +618,27 @@ static int __kprobes trap_compare(long v1, long v2)
>>   }
>>   
>>   /*
>> + * Helper to check if a given instruction is a conditional branch
>> + * Derived from the conditional checks in analyse_instr()
>> + */
>> +bool __kprobes is_conditional_branch(unsigned int instr)
>> +{
>> +	unsigned int opcode = instr >> 26;
>> +
>> +	if (opcode == 16)	/* bc, bca, bcl, bcla */
>> +		return true;
>> +	if (opcode == 19) {
>> +		switch ((instr >> 1) & 0x3ff) {
>> +		case 16:	/* bclr, bclrl */
>> +		case 528:	/* bcctr, bcctrl */
>> +		case 560:	/* bctar, bctarl */
>> +			return true;
>> +		}
>> +	}
>> +	return false;
>> +}
>> +
>> +/*
>>    * Elements of 32-bit rotate and mask instructions.
>>    */
>>   #define MASK32(mb, me)	((0xffffffffUL >> (mb)) + \
>> @@ -2018,3 +2039,4 @@ int __kprobes emulate_step(struct pt_regs *regs, unsigned int instr)
>>   	regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
>>   	return 1;
>>   }
>> +
> This seems unneeded linefeed :)


  :-) I will remove the extra line.


Thanks and Regards,
Anju
> Thank you,
>