Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 631 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
new file mode 100644
index 00000000000..4f2a852299b
--- /dev/null
+++ b/arch/x86_64/kernel/kprobes.c
@@ -0,0 +1,631 @@
+/*
+ *  Kernel Probes (KProbes)
+ *  arch/x86_64/kernel/kprobes.c
+ *
+ * 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.
+ *
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2004
+ *
+ * 2002-Oct     Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
+ *              Probes initial implementation ( includes contributions from
+ *              Rusty Russell).
+ * 2004-July    Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
+ *              interface to access function arguments.
+ * 2004-Oct     Jim Keniston <kenistoj@us.ibm.com> and Prasanna S Panchamukhi
+ *              <prasanna@in.ibm.com> adapted for x86_64
+ * 2005-Mar     Roland McGrath <roland@redhat.com>
+ *              Fixed to handle %rip-relative addressing mode correctly.
+ */
+
+#include <linux/config.h>
+#include <linux/kprobes.h>
+#include <linux/ptrace.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/preempt.h>
+#include <linux/moduleloader.h>
+
+#include <asm/pgtable.h>
+#include <asm/kdebug.h>
+
+static DECLARE_MUTEX(kprobe_mutex);
+
+/* kprobe_status settings */
+#define KPROBE_HIT_ACTIVE       0x00000001
+#define KPROBE_HIT_SS           0x00000002
+
+static struct kprobe *current_kprobe;
+static unsigned long kprobe_status, kprobe_old_rflags, kprobe_saved_rflags;
+static struct pt_regs jprobe_saved_regs;
+static long *jprobe_saved_rsp;
+static kprobe_opcode_t *get_insn_slot(void);
+static void free_insn_slot(kprobe_opcode_t *slot);
+void jprobe_return_end(void);
+
+/* copy of the kernel stack at the probe fire time */
+static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE];
+
+/*
+ * returns non-zero if opcode modifies the interrupt flag.
+ */
+static inline int is_IF_modifier(kprobe_opcode_t *insn)
+{
+        switch (*insn) {
+        case 0xfa:              /* cli */
+        case 0xfb:              /* sti */
+        case 0xcf:              /* iret/iretd */
+        case 0x9d:              /* popf/popfd */
+                return 1;
+        }
+
+        if (*insn  >= 0x40 && *insn <= 0x4f && *++insn == 0xcf)
+                return 1;
+        return 0;
+}
+
+int arch_prepare_kprobe(struct kprobe *p)
+{
+        /* insn: must be on special executable page on x86_64. */
+        up(&kprobe_mutex);
+        p->ainsn.insn = get_insn_slot();
+        down(&kprobe_mutex);
+        if (!p->ainsn.insn) {
+                return -ENOMEM;
+        }
+        return 0;
+}
+
+/*
+ * Determine if the instruction uses the %rip-relative addressing mode.
+ * If it does, return the address of the 32-bit displacement word.
+ * If not, return null.
+ */
+static inline s32 *is_riprel(u8 *insn)
+{
+#define W(row,b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,ba,bb,bc,bd,be,bf)                \
+        (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
+          (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
+          (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
+          (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
+         << (row % 64))
+        static const u64 onebyte_has_modrm[256 / 64] = {
+                /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
+                /*      -------------------------------         */
+                W(0x00, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 00 */
+                W(0x10, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 10 */
+                W(0x20, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0)| /* 20 */
+                W(0x30, 1,1,1,1,0,0,0,0,1,1,1,1,0,0,0,0), /* 30 */
+                W(0x40, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 40 */
+                W(0x50, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 50 */
+                W(0x60, 0,0,1,1,0,0,0,0,0,1,0,1,0,0,0,0)| /* 60 */
+                W(0x70, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 70 */
+                W(0x80, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 80 */
+                W(0x90, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 90 */
+                W(0xa0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* a0 */
+                W(0xb0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* b0 */
+                W(0xc0, 1,1,0,0,1,1,1,1,0,0,0,0,0,0,0,0)| /* c0 */
+                W(0xd0, 1,1,1,1,0,0,0,0,1,1,1,1,1,1,1,1)| /* d0 */
+                W(0xe0, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* e0 */
+                W(0xf0, 0,0,0,0,0,0,1,1,0,0,0,0,0,0,1,1)  /* f0 */
+                /*      -------------------------------         */
+                /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
+        };
+        static const u64 twobyte_has_modrm[256 / 64] = {
+                /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
+                /*      -------------------------------         */
+                W(0x00, 1,1,1,1,0,0,0,0,0,0,0,0,0,1,0,1)| /* 0f */
+                W(0x10, 1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0)| /* 1f */
+                W(0x20, 1,1,1,1,1,0,1,0,1,1,1,1,1,1,1,1)| /* 2f */
+                W(0x30, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0), /* 3f */
+                W(0x40, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 4f */
+                W(0x50, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 5f */
+                W(0x60, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 6f */
+                W(0x70, 1,1,1,1,1,1,1,0,0,0,0,0,1,1,1,1), /* 7f */
+                W(0x80, 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0)| /* 8f */
+                W(0x90, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* 9f */
+                W(0xa0, 0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,1)| /* af */
+                W(0xb0, 1,1,1,1,1,1,1,1,0,0,1,1,1,1,1,1), /* bf */
+                W(0xc0, 1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0)| /* cf */
+                W(0xd0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* df */
+                W(0xe0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1)| /* ef */
+                W(0xf0, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0)  /* ff */
+                /*      -------------------------------         */
+                /*      0 1 2 3 4 5 6 7 8 9 a b c d e f         */
+        };
+#undef  W
+        int need_modrm;
+
+        /* Skip legacy instruction prefixes.  */
+        while (1) {
+                switch (*insn) {
+                case 0x66:
+                case 0x67:
+                case 0x2e:
+                case 0x3e:
+                case 0x26:
+                case 0x64:
+                case 0x65:
+                case 0x36:
+                case 0xf0:
+                case 0xf3:
+                case 0xf2:
+                        ++insn;
+                        continue;
+                }
+                break;
+        }
+
+        /* Skip REX instruction prefix.  */
+        if ((*insn & 0xf0) == 0x40)
+                ++insn;
+
+        if (*insn == 0x0f) {    /* Two-byte opcode.  */
+                ++insn;
+                need_modrm = test_bit(*insn, twobyte_has_modrm);
+        } else {                /* One-byte opcode.  */
+                need_modrm = test_bit(*insn, onebyte_has_modrm);
+        }
+
+        if (need_modrm) {
+                u8 modrm = *++insn;
+                if ((modrm & 0xc7) == 0x05) { /* %rip+disp32 addressing mode */
+                        /* Displacement follows ModRM byte.  */
+                        return (s32 *) ++insn;
+                }
+        }
+
+        /* No %rip-relative addressing mode here.  */
+        return NULL;
+}
+
+void arch_copy_kprobe(struct kprobe *p)
+{
+        s32 *ripdisp;
+        memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE);
+        ripdisp = is_riprel(p->ainsn.insn);
+        if (ripdisp) {
+                /*
+                 * The copied instruction uses the %rip-relative
+                 * addressing mode.  Adjust the displacement for the
+                 * difference between the original location of this
+                 * instruction and the location of the copy that will
+                 * actually be run.  The tricky bit here is making sure
+                 * that the sign extension happens correctly in this
+                 * calculation, since we need a signed 32-bit result to
+                 * be sign-extended to 64 bits when it's added to the
+                 * %rip value and yield the same 64-bit result that the
+                 * sign-extension of the original signed 32-bit
+                 * displacement would have given.
+                 */
+                s64 disp = (u8 *) p->addr + *ripdisp - (u8 *) p->ainsn.insn;
+                BUG_ON((s64) (s32) disp != disp); /* Sanity check.  */
+                *ripdisp = disp;
+        }
+}
+
+void arch_remove_kprobe(struct kprobe *p)
+{
+        up(&kprobe_mutex);
+        free_insn_slot(p->ainsn.insn);
+        down(&kprobe_mutex);
+}
+
+static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs)
+{
+        *p->addr = p->opcode;
+        regs->rip = (unsigned long)p->addr;
+}
+
+static void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+{
+        regs->eflags |= TF_MASK;
+        regs->eflags &= ~IF_MASK;
+        /*single step inline if the instruction is an int3*/
+        if (p->opcode == BREAKPOINT_INSTRUCTION)
+                regs->rip = (unsigned long)p->addr;
+        else
+                regs->rip = (unsigned long)p->ainsn.insn;
+}
+
+/*
+ * Interrupts are disabled on entry as trap3 is an interrupt gate and they
+ * remain disabled thorough out this function.
+ */
+int kprobe_handler(struct pt_regs *regs)
+{
+        struct kprobe *p;
+        int ret = 0;
+        kprobe_opcode_t *addr = (kprobe_opcode_t *)(regs->rip - sizeof(kprobe_opcode_t));
+
+        /* We're in an interrupt, but this is clear and BUG()-safe. */
+        preempt_disable();
+
+        /* Check we're not actually recursing */
+        if (kprobe_running()) {
+                /* We *are* holding lock here, so this is safe.
+                   Disarm the probe we just hit, and ignore it. */
+                p = get_kprobe(addr);
+                if (p) {
+                        if (kprobe_status == KPROBE_HIT_SS) {
+                                regs->eflags &= ~TF_MASK;
+                                regs->eflags |= kprobe_saved_rflags;
+                                unlock_kprobes();
+                                goto no_kprobe;
+                        }
+                        disarm_kprobe(p, regs);
+                        ret = 1;
+                } else {
+                        p = current_kprobe;
+                        if (p->break_handler && p->break_handler(p, regs)) {
+                                goto ss_probe;
+                        }
+                }
+                /* If it's not ours, can't be delete race, (we hold lock). */
+                goto no_kprobe;
+        }
+
+        lock_kprobes();
+        p = get_kprobe(addr);
+        if (!p) {
+                unlock_kprobes();
+                if (*addr != BREAKPOINT_INSTRUCTION) {
+                        /*
+                         * The breakpoint instruction was removed right
+                         * after we hit it.  Another cpu has removed
+                         * either a probepoint or a debugger breakpoint
+                         * at this address.  In either case, no further
+                         * handling of this interrupt is appropriate.
+                         */
+                        ret = 1;
+                }
+                /* Not one of ours: let kernel handle it */
+                goto no_kprobe;
+        }
+
+        kprobe_status = KPROBE_HIT_ACTIVE;
+        current_kprobe = p;
+        kprobe_saved_rflags = kprobe_old_rflags
+            = (regs->eflags & (TF_MASK | IF_MASK));
+        if (is_IF_modifier(p->ainsn.insn))
+                kprobe_saved_rflags &= ~IF_MASK;
+
+        if (p->pre_handler && p->pre_handler(p, regs))
+                /* handler has already set things up, so skip ss setup */
+                return 1;
+
+ss_probe:
+        prepare_singlestep(p, regs);
+        kprobe_status = KPROBE_HIT_SS;
+        return 1;
+
+no_kprobe:
+        preempt_enable_no_resched();
+        return ret;
+}
+
+/*
+ * Called after single-stepping.  p->addr is the address of the
+ * instruction whose first byte has been replaced by the "int 3"
+ * instruction.  To avoid the SMP problems that can occur when we
+ * temporarily put back the original opcode to single-step, we
+ * single-stepped a copy of the instruction.  The address of this
+ * copy is p->ainsn.insn.
+ *
+ * This function prepares to return from the post-single-step
+ * interrupt.  We have to fix up the stack as follows:
+ *
+ * 0) Except in the case of absolute or indirect jump or call instructions,
+ * the new rip is relative to the copied instruction.  We need to make
+ * it relative to the original instruction.
+ *
+ * 1) If the single-stepped instruction was pushfl, then the TF and IF
+ * flags are set in the just-pushed eflags, and may need to be cleared.
+ *
+ * 2) If the single-stepped instruction was a call, the return address
+ * that is atop the stack is the address following the copied instruction.
+ * We need to make it the address following the original instruction.
+ */
+static void resume_execution(struct kprobe *p, struct pt_regs *regs)
+{
+        unsigned long *tos = (unsigned long *)regs->rsp;
+        unsigned long next_rip = 0;
+        unsigned long copy_rip = (unsigned long)p->ainsn.insn;
+        unsigned long orig_rip = (unsigned long)p->addr;
+        kprobe_opcode_t *insn = p->ainsn.insn;
+
+        /*skip the REX prefix*/
+        if (*insn >= 0x40 && *insn <= 0x4f)
+                insn++;
+
+        switch (*insn) {
+        case 0x9c:              /* pushfl */
+                *tos &= ~(TF_MASK | IF_MASK);
+                *tos |= kprobe_old_rflags;
+                break;
+        case 0xe8:              /* call relative - Fix return addr */
+                *tos = orig_rip + (*tos - copy_rip);
+                break;
+        case 0xff:
+                if ((*insn & 0x30) == 0x10) {
+                        /* call absolute, indirect */
+                        /* Fix return addr; rip is correct. */
+                        next_rip = regs->rip;
+                        *tos = orig_rip + (*tos - copy_rip);
+                } else if (((*insn & 0x31) == 0x20) ||  /* jmp near, absolute indirect */
+                           ((*insn & 0x31) == 0x21)) {  /* jmp far, absolute indirect */
+                        /* rip is correct. */
+                        next_rip = regs->rip;
+                }
+                break;
+        case 0xea:              /* jmp absolute -- rip is correct */
+                next_rip = regs->rip;
+                break;
+        default:
+                break;
+        }
+
+        regs->eflags &= ~TF_MASK;
+        if (next_rip) {
+                regs->rip = next_rip;
+        } else {
+                regs->rip = orig_rip + (regs->rip - copy_rip);
+        }
+}
+
+/*
+ * Interrupts are disabled on entry as trap1 is an interrupt gate and they
+ * remain disabled thoroughout this function.  And we hold kprobe lock.
+ */
+int post_kprobe_handler(struct pt_regs *regs)
+{
+        if (!kprobe_running())
+                return 0;
+
+        if (current_kprobe->post_handler)
+                current_kprobe->post_handler(current_kprobe, regs, 0);
+
+        resume_execution(current_kprobe, regs);
+        regs->eflags |= kprobe_saved_rflags;
+
+        unlock_kprobes();
+        preempt_enable_no_resched();
+
+        /*
+         * if somebody else is singlestepping across a probe point, eflags
+         * will have TF set, in which case, continue the remaining processing
+         * of do_debug, as if this is not a probe hit.
+         */
+        if (regs->eflags & TF_MASK)
+                return 0;
+
+        return 1;
+}
+
+/* Interrupts disabled, kprobe_lock held. */
+int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
+{
+        if (current_kprobe->fault_handler
+            && current_kprobe->fault_handler(current_kprobe, regs, trapnr))
+                return 1;
+
+        if (kprobe_status & KPROBE_HIT_SS) {
+                resume_execution(current_kprobe, regs);
+                regs->eflags |= kprobe_old_rflags;
+
+                unlock_kprobes();
+                preempt_enable_no_resched();
+        }
+        return 0;
+}
+
+/*
+ * Wrapper routine for handling exceptions.
+ */
+int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val,
+                             void *data)
+{
+        struct die_args *args = (struct die_args *)data;
+        switch (val) {
+        case DIE_INT3:
+                if (kprobe_handler(args->regs))
+                        return NOTIFY_STOP;
+                break;
+        case DIE_DEBUG:
+                if (post_kprobe_handler(args->regs))
+                        return NOTIFY_STOP;
+                break;
+        case DIE_GPF:
+                if (kprobe_running() &&
+                    kprobe_fault_handler(args->regs, args->trapnr))
+                        return NOTIFY_STOP;
+                break;
+        case DIE_PAGE_FAULT:
+                if (kprobe_running() &&
+                    kprobe_fault_handler(args->regs, args->trapnr))
+                        return NOTIFY_STOP;
+                break;
+        default:
+                break;
+        }
+        return NOTIFY_DONE;
+}
+
+int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        struct jprobe *jp = container_of(p, struct jprobe, kp);
+        unsigned long addr;
+
+        jprobe_saved_regs = *regs;
+        jprobe_saved_rsp = (long *) regs->rsp;
+        addr = (unsigned long)jprobe_saved_rsp;
+        /*
+         * As Linus pointed out, gcc assumes that the callee
+         * owns the argument space and could overwrite it, e.g.
+         * tailcall optimization. So, to be absolutely safe
+         * we also save and restore enough stack bytes to cover
+         * the argument area.
+         */
+        memcpy(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr));
+        regs->eflags &= ~IF_MASK;
+        regs->rip = (unsigned long)(jp->entry);
+        return 1;
+}
+
+void jprobe_return(void)
+{
+        preempt_enable_no_resched();
+        asm volatile ("       xchg   %%rbx,%%rsp     \n"
+                      "       int3                      \n"
+                      "       .globl jprobe_return_end  \n"
+                      "       jprobe_return_end:        \n"
+                      "       nop                       \n"::"b"
+                      (jprobe_saved_rsp):"memory");
+}
+
+int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs)
+{
+        u8 *addr = (u8 *) (regs->rip - 1);
+        unsigned long stack_addr = (unsigned long)jprobe_saved_rsp;
+        struct jprobe *jp = container_of(p, struct jprobe, kp);
+
+        if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) {
+                if ((long *)regs->rsp != jprobe_saved_rsp) {
+                        struct pt_regs *saved_regs =
+                            container_of(jprobe_saved_rsp, struct pt_regs, rsp);
+                        printk("current rsp %p does not match saved rsp %p\n",
+                               (long *)regs->rsp, jprobe_saved_rsp);
+                        printk("Saved registers for jprobe %p\n", jp);
+                        show_registers(saved_regs);
+                        printk("Current registers\n");
+                        show_registers(regs);
+                        BUG();
+                }
+                *regs = jprobe_saved_regs;
+                memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack,
+                       MIN_STACK_SIZE(stack_addr));
+                return 1;
+        }
+        return 0;
+}
+
+/*
+ * kprobe->ainsn.insn points to the copy of the instruction to be single-stepped.
+ * By default on x86_64, pages we get from kmalloc or vmalloc are not
+ * executable.  Single-stepping an instruction on such a page yields an
+ * oops.  So instead of storing the instruction copies in their respective
+ * kprobe objects, we allocate a page, map it executable, and store all the
+ * instruction copies there.  (We can allocate additional pages if somebody
+ * inserts a huge number of probes.)  Each page can hold up to INSNS_PER_PAGE
+ * instruction slots, each of which is MAX_INSN_SIZE*sizeof(kprobe_opcode_t)
+ * bytes.
+ */
+#define INSNS_PER_PAGE (PAGE_SIZE/(MAX_INSN_SIZE*sizeof(kprobe_opcode_t)))
+struct kprobe_insn_page {
+        struct hlist_node hlist;
+        kprobe_opcode_t *insns;         /* page of instruction slots */
+        char slot_used[INSNS_PER_PAGE];
+        int nused;
+};
+
+static struct hlist_head kprobe_insn_pages;
+
+/**
+ * get_insn_slot() - Find a slot on an executable page for an instruction.
+ * We allocate an executable page if there's no room on existing ones.
+ */
+static kprobe_opcode_t *get_insn_slot(void)
+{
+        struct kprobe_insn_page *kip;
+        struct hlist_node *pos;
+
+        hlist_for_each(pos, &kprobe_insn_pages) {
+                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
+                if (kip->nused < INSNS_PER_PAGE) {
+                        int i;
+                        for (i = 0; i < INSNS_PER_PAGE; i++) {
+                                if (!kip->slot_used[i]) {
+                                        kip->slot_used[i] = 1;
+                                        kip->nused++;
+                                        return kip->insns + (i*MAX_INSN_SIZE);
+                                }
+                        }
+                        /* Surprise!  No unused slots.  Fix kip->nused. */
+                        kip->nused = INSNS_PER_PAGE;
+                }
+        }
+
+        /* All out of space.  Need to allocate a new page. Use slot 0.*/
+        kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
+        if (!kip) {
+                return NULL;
+        }
+
+        /*
+         * For the %rip-relative displacement fixups to be doable, we
+         * need our instruction copy to be within +/- 2GB of any data it
+         * might access via %rip.  That is, within 2GB of where the
+         * kernel image and loaded module images reside.  So we allocate
+         * a page in the module loading area.
+         */
+        kip->insns = module_alloc(PAGE_SIZE);
+        if (!kip->insns) {
+                kfree(kip);
+                return NULL;
+        }
+        INIT_HLIST_NODE(&kip->hlist);
+        hlist_add_head(&kip->hlist, &kprobe_insn_pages);
+        memset(kip->slot_used, 0, INSNS_PER_PAGE);
+        kip->slot_used[0] = 1;
+        kip->nused = 1;
+        return kip->insns;
+}
+
+/**
+ * free_insn_slot() - Free instruction slot obtained from get_insn_slot().
+ */
+static void free_insn_slot(kprobe_opcode_t *slot)
+{
+        struct kprobe_insn_page *kip;
+        struct hlist_node *pos;
+
+        hlist_for_each(pos, &kprobe_insn_pages) {
+                kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
+                if (kip->insns <= slot
+                    && slot < kip->insns+(INSNS_PER_PAGE*MAX_INSN_SIZE)) {
+                        int i = (slot - kip->insns) / MAX_INSN_SIZE;
+                        kip->slot_used[i] = 0;
+                        kip->nused--;
+                        if (kip->nused == 0) {
+                                /*
+                                 * Page is no longer in use.  Free it unless
+                                 * it's the last one.  We keep the last one
+                                 * so as not to have to set it up again the
+                                 * next time somebody inserts a probe.
+                                 */
+                                hlist_del(&kip->hlist);
+                                if (hlist_empty(&kprobe_insn_pages)) {
+                                        INIT_HLIST_NODE(&kip->hlist);
+                                        hlist_add_head(&kip->hlist,
+                                                &kprobe_insn_pages);
+                                } else {
+                                        module_free(NULL, kip->insns);
+                                        kfree(kip);
+                                }
+                        }
+                        return;
+                }
+        }
+}