powerpc: Uprobes port to powerpc

This is the port of uprobes to powerpc. Usage is similar to x86.

[root@xxxx ~]# ./bin/perf probe -x /lib64/libc.so.6 malloc
Added new event:
  probe_libc:malloc    (on 0xb4860)

You can now use it in all perf tools, such as:

	perf record -e probe_libc:malloc -aR sleep 1

[root@xxxx ~]# ./bin/perf record -e probe_libc:malloc -aR sleep 20
[ perf record: Woken up 22 times to write data ]
[ perf record: Captured and wrote 5.843 MB perf.data (~255302 samples) ]
[root@xxxx ~]# ./bin/perf report --stdio
...

    69.05%           tar  libc-2.12.so   [.] malloc
    28.57%            rm  libc-2.12.so   [.] malloc
     1.32%  avahi-daemon  libc-2.12.so   [.] malloc
     0.58%          bash  libc-2.12.so   [.] malloc
     0.28%          sshd  libc-2.12.so   [.] malloc
     0.08%    irqbalance  libc-2.12.so   [.] malloc
     0.05%         bzip2  libc-2.12.so   [.] malloc
     0.04%         sleep  libc-2.12.so   [.] malloc
     0.03%    multipathd  libc-2.12.so   [.] malloc
     0.01%      sendmail  libc-2.12.so   [.] malloc
     0.01%     automount  libc-2.12.so   [.] malloc

The trap_nr addition patch is a prereq.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 184 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
new file mode 100644
index 000000000000..d2d46d1014f8
--- /dev/null
+++ b/arch/powerpc/kernel/uprobes.c
@@ -0,0 +1,184 @@
+/*
+ * User-space Probes (UProbes) for powerpc
+ *
+ * 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 IBM Corporation, 2007-2012
+ *
+ * Adapted from the x86 port by Ananth N Mavinakayanahalli <ananth@in.ibm.com>
+ */
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/ptrace.h>
+#include <linux/uprobes.h>
+#include <linux/uaccess.h>
+#include <linux/kdebug.h>
+
+#include <asm/sstep.h>
+
+#define UPROBE_TRAP_NR  UINT_MAX
+
+/**
+ * arch_uprobe_analyze_insn
+ * @mm: the probed address space.
+ * @arch_uprobe: the probepoint information.
+ * @addr: vaddr to probe.
+ * Return 0 on success or a -ve number on error.
+ */
+int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
+                struct mm_struct *mm, unsigned long addr)
+{
+        if (addr & 0x03)
+                return -EINVAL;
+
+        /*
+         * We currently don't support a uprobe on an already
+         * existing breakpoint instruction underneath
+         */
+        if (is_trap(auprobe->ainsn))
+                return -ENOTSUPP;
+        return 0;
+}
+
+/*
+ * arch_uprobe_pre_xol - prepare to execute out of line.
+ * @auprobe: the probepoint information.
+ * @regs: reflects the saved user state of current task.
+ */
+int arch_uprobe_pre_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+        struct arch_uprobe_task *autask = &current->utask->autask;
+
+        autask->saved_trap_nr = current->thread.trap_nr;
+        current->thread.trap_nr = UPROBE_TRAP_NR;
+        regs->nip = current->utask->xol_vaddr;
+        return 0;
+}
+
+/**
+ * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
+ * @regs: Reflects the saved state of the task after it has hit a breakpoint
+ * instruction.
+ * Return the address of the breakpoint instruction.
+ */
+unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
+{
+        return instruction_pointer(regs);
+}
+
+/*
+ * If xol insn itself traps and generates a signal (SIGILL/SIGSEGV/etc),
+ * then detect the case where a singlestepped instruction jumps back to its
+ * own address. It is assumed that anything like do_page_fault/do_trap/etc
+ * sets thread.trap_nr != UINT_MAX.
+ *
+ * arch_uprobe_pre_xol/arch_uprobe_post_xol save/restore thread.trap_nr,
+ * arch_uprobe_xol_was_trapped() simply checks that ->trap_nr is not equal to
+ * UPROBE_TRAP_NR == UINT_MAX set by arch_uprobe_pre_xol().
+ */
+bool arch_uprobe_xol_was_trapped(struct task_struct *t)
+{
+        if (t->thread.trap_nr != UPROBE_TRAP_NR)
+                return true;
+
+        return false;
+}
+
+/*
+ * Called after single-stepping. 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.
+ *
+ * This function prepares to resume execution after the single-step.
+ */
+int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+        struct uprobe_task *utask = current->utask;
+
+        WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
+
+        current->thread.trap_nr = utask->autask.saved_trap_nr;
+
+        /*
+         * On powerpc, except for loads and stores, most instructions
+         * including ones that alter code flow (branches, calls, returns)
+         * are emulated in the kernel. We get here only if the emulation
+         * support doesn't exist and have to fix-up the next instruction
+         * to be executed.
+         */
+        regs->nip = utask->vaddr + MAX_UINSN_BYTES;
+        return 0;
+}
+
+/* callback routine for handling exceptions. */
+int arch_uprobe_exception_notify(struct notifier_block *self,
+                                unsigned long val, void *data)
+{
+        struct die_args *args = data;
+        struct pt_regs *regs = args->regs;
+
+        /* regs == NULL is a kernel bug */
+        if (WARN_ON(!regs))
+                return NOTIFY_DONE;
+
+        /* We are only interested in userspace traps */
+        if (!user_mode(regs))
+                return NOTIFY_DONE;
+
+        switch (val) {
+        case DIE_BPT:
+                if (uprobe_pre_sstep_notifier(regs))
+                        return NOTIFY_STOP;
+                break;
+        case DIE_SSTEP:
+                if (uprobe_post_sstep_notifier(regs))
+                        return NOTIFY_STOP;
+        default:
+                break;
+        }
+        return NOTIFY_DONE;
+}
+
+/*
+ * This function gets called when XOL instruction either gets trapped or
+ * the thread has a fatal signal, so reset the instruction pointer to its
+ * probed address.
+ */
+void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+        struct uprobe_task *utask = current->utask;
+
+        current->thread.trap_nr = utask->autask.saved_trap_nr;
+        instruction_pointer_set(regs, utask->vaddr);
+}
+
+/*
+ * See if the instruction can be emulated.
+ * Returns true if instruction was emulated, false otherwise.
+ */
+bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
+{
+        int ret;
+
+        /*
+         * emulate_step() returns 1 if the insn was successfully emulated.
+         * For all other cases, we need to single-step in hardware.
+         */
+        ret = emulate_step(regs, auprobe->ainsn);
+        if (ret > 0)
+                return true;
+
+        return false;
+}