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Message-ID: <20160524111411.GB18654@naverao1-tp.localdomain> Date: Tue, 24 May 2016 16:44:11 +0530 From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> To: Anju T <anju@...ux.vnet.ibm.com> Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, ananth@...ibm.com, paulus@...ba.org, srikar@...ux.vnet.ibm.com, benh@...nel.crashing.org, mpe@...erman.id.au, hemant@...ux.vnet.ibm.com, mahesh@...ux.vnet.ibm.com, mhiramat@...nel.org Subject: Re: [RFC PATCH v2 1/3] arch/powerpc : Add detour buffer support for optprobes On 2016/05/19 08:40PM, Anju T wrote: > 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@...ux.vnet.ibm.com> > --- > 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) I think this will not work. Looking through the code, I don't see us saving/restoring CFAR across interrupts. Also, per the ISA: "The Come-From Address Register (CFAR) is a 64-bit register. When an rfebb, rfid, or rfscv instruction is executed, the register is set to the effective address of the instruction." So, it looks like we actually can't save/restore it anyway. Regardless, NIP is the same as the kprobe'd address, so you should be able to either use immediate loads or load the address from kprobe structure. - Naveen
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