Anju T Sudhakar <anju@xxxxxxxxxxxxxxxxxx> writes:
Detour buffer contains instructions to create an in memory pt_regs.That's good detail, but it's hard to follow for someone who isn't
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.
familiar with with kprobes/optprobes etc. You don't even tell us what an
optprobe is :)
So can you provide a bit more background before diving into the specific
details.
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
candidates ?
diff --git a/Documentation/features/debug/optprobes/arch-support.txt b/Documentation/features/debug/optprobes/arch-support.txtWe don't support them for modules yet, so maybe it's premature to flip
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 |
that?
diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.cThis sets off my "no-locking-visible" detector. I assume there's some
new file mode 100644
index 0000000..fb5e62d
--- /dev/null
+++ b/arch/powerpc/kernel/optprobes.c
@@ -0,0 +1,331 @@
+/*
+ * 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;
locking somewhere else that makes this work?
+ return &optinsn_slot;That probably warrants a TODO or FIXME.
+}
+
+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.
+ */It may not matter in practice, but leaving most of regs uninitialised
+ if (!is_kernel_addr((unsigned long)p->addr))
+ return 0;
+
+ regs.nip = (unsigned long)p->addr;
+ regs.trap = 0x0;
+ regs.msr = MSR_KERNEL;
seems a bit fishy. I'd prefer if we zeroed it first.
+ /*Can you spell out why it can't be a conditional branch.
+ * Ensure that the instruction is not a conditional branch,
+ * and that can be emulated.What is that protecting against? Because on powerpc it doesn't actually
+ */
+ if (!is_conditional_branch(*p->ainsn.insn) &&
+ analyse_instr(&op, ®s, *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);
disable interrupts, it just masks some of them, the perf interrupt for
example can still run.
+I can't say I love those patch functions. A PC-relative load would be
+ 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);
+}
cleaner, but I guess that's ugly/expensive on current CPUs.
diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.SSo this is what made me originally reply to this patch. This
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)
save/restore sequence.
I'm not clear on why this is what we need to save/restore.
Aren't we essentially just interposing a function call? If so do we need
to save/restore all of these? eg. MSR/DAR/DSISR. Non-volatile GPRs? And
why are we pretending there was a 0x700 trap?
Is it because we're going to end up emulating the instruction and so we
need everything in pt_regs ?
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.cWe already have some similar routines in code_patching.c/h. Can you move
index 3362299..895dcdd 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;
+
this in there instead?
cheers