1. 02 8月, 2008 1 次提交
  2. 05 3月, 2008 1 次提交
  3. 17 10月, 2007 2 次提交
  4. 20 7月, 2007 1 次提交
  5. 05 5月, 2007 1 次提交
  6. 20 9月, 2006 1 次提交
  7. 01 8月, 2006 1 次提交
  8. 27 6月, 2006 1 次提交
  9. 27 3月, 2006 1 次提交
    • M
      [PATCH] x86: kprobes-booster · 311ac88f
      Masami Hiramatsu 提交于
      Current kprobe copies the original instruction at the probe point and replaces
      it with a breakpoint instruction (int3).  When the kernel hits the probe
      point, kprobe handler is invoked.  And the copied instruction is single-step
      executed on the copied buffer (not on the original address) by kprobe.  After
      that, the kprobe checks registers and modify it (if need) as if the
      instructions was executed on the original address.
      
      My proposal is based on the fact there are many instructions which do NOT
      require the register modification after the single-step execution.  When the
      copied instruction is a kind of them, kprobe just jumps back to the next
      instruction after single-step execution.  If so, why don't we execute those
      instructions directly?
      
      With kprobe-booster patch, kprobes will execute a copied instruction directly
      and (if need) jump back to original code.  This direct execution is executed
      when the kprobe don't have both post_handler and break_handler, and the copied
      instruction can be executed directly.
      
      I sorted instructions which can be executed directly or not;
      
      - Call instructions are NG(can not be executed directly).
        We should correct the return address pushed into top of stack.
      - Indirect instructions except for absolute indirect-jumps
        are NG. Those instructions changes EIP randomly. We should
        check EIP and correct it.
      - Instructions that change EIP beyond the range of the
        instruction buffer are NG.
      - Instructions that change EIP to tail 5 bytes of the
        instruction buffer (it is the size of a jump instruction).
        We must write a jump instruction which backs to original
        kernel code in the instruction buffer.
      - Break point instruction is NG. We should not touch EIP and
        pass to other handlers.
      - Absolute direct/indirect jumps are OK.- Conditional Jumps are NG.
      - Halt and software-interruptions are NG. Because it will stay on
        the instruction buffer of kprobes.
      - Prefixes are NG.
      - Unknown/reserved opcode is NG.
      - Other 1 byte instructions are OK. But those instructions need a
        jump back code.
      - 2 bytes instructions are mapped sparsely. So, in this release,
        this patch don't boost those instructions.
      
      >From Intel's IA-32 opcode map described in IA-32 Intel Architecture Software
      Developer's Manual Vol.2 B, I determined that following opcodes are not
      boostable.
      
      - 0FH (2byte escape)
      - 70H - 7FH (Jump on condition)
      - 9AH (Call) and 9CH (Pushf)
      - C0H-C1H (Grp 2: includes reserved opcode)
      - C6H-C7H (Grp11: includes reserved opcode)
      - CCH-CEH (Software-interrupt)
      - D0H-D3H (Grp2: includes reserved opcode)
      - D6H (Reserved)
      - D8H-DFH (Coprocessor)
      - E0H-E3H (loop/conditional jump)
      - E8H (Call)
      - F0H-F3H (Prefixes and reserved)
      - F4H (Halt)
      - F6H-F7H (Grp3: includes reserved opcode)
      - FEH-FFH(Grp4,5: includes reserved opcode)
      
      Kprobe-booster checks whether target instruction can be boosted (can be
      executed directly) at arch_copy_kprobe() function.  If the target instruction
      can be boosted, it clears "boostable" flag.  If not, it sets "boostable" flag
      -1.  This is disabled status.  In resume_execution() function, If "boostable"
      flag is cleared, kprobe-booster measures the size of the target instruction
      and sets "boostable" flag 1.
      
      In kprobe_handler(), kprobe checks the "boostable" flag.  If the flag is 1, it
      resets current kprobe and executes instruction buffer directly instead of
      single stepping.
      
      When unregistering a boosted kprobe, it calls synchronize_sched()
      after "int3" is removed. So we can ensure followings after
      the synchronize_sched() called.
      - interrupt handlers are finished on all CPUs.
      - instruction buffer is not executed on all CPUs.
      And we can release the boosted kprobe safely.
      
      And also, on preemptible kernel, the booster is not enabled where the kernel
      preemption is enabled.  So, there are no preempted threads on the instruction
      buffer.
      
      The description of kretprobe-booster:
      ====================================
      
      In the normal operation, kretprobe make a target function return to trampoline
      code.  And a kprobe (called trampoline_probe) have been inserted at the
      trampoline code.  When the kernel hits this kprobe, it calls kretprobe's
      handler and it returns to original return address.
      
      Kretprobe-booster patch removes the trampoline_probe.  It allows the
      trampoline code to call kretprobe's handler directly instead of invoking
      kprobe.  And tranpoline code returns to original return address.
      
      This new trampoline code stores and restores registers, so the kretprobe
      handler is still able to access those registers.
      
      Current kprobe has about 1.3 usec/probe(*) overhead, and kprobe-booster patch
      reduces it to 0.6 usec/probe(*).  Also current kretprobe has about 2.0
      usec/probe(*) overhead.  Kprobe-booster patch reduces it to 1.3 usec/probe(*),
      and the combination of both kprobe-booster patch and kretprobe-booster patch
      reduces it to 0.9 usec/probe(*).
      
      I expect the combination of both patches can reduce half of a probing
      overhead.
      
      Performance numbers strongly depend on the processor model.
      
      Andrew Morton wrote:
      > These preempt tricks look rather nasty.  Can you please describe what the
      > problem is, precisely?  And how this code avoids it?  Perhaps we can find
      > something cleaner.
      
      The problem is how to remove the copied instructions of the
      kprobe *safely* on the preemptable kernel (CONFIG_PREEMPT=y).
      
      Kprobes basically executes the following actions;
      
      (1)int3
      (2)preempt_disable()
      (3)kprobe_prehandler()
      (4)copied instructioin(single step)
      (5)kprobe_posthandler()
      (6)preempt_enable()
      (7)return to the original code
      
      During the execution of copied instruction, preemption is
      disabled (from step (2) to (6)).
      When unregistering the probes, Kprobe waits for RCU
      quiescent state by using synchronize_sched() after removing
      int3 instruction.
      Thus we can ensure the copied instruction is not executed.
      
      On the other hand, kprobe-booster executes the following actions;
      
      (1)int3
      (2)preempt_disable()
      (3)kprobe_prehandler()
      (4)preempt_enable()             <-- this one is added by my patch
      (5)copied instruction(direct execution)
      (6)jmp back to the original code
      
      The problem is that we have no way to prevent preemption on
      step (5) or (6). We cannot call preempt_disable() after step (6),
      because there are no rooms to do that. Thus, some other
      processes may be preempted at step(5) or (6) on preemptable kernel.
      And I couldn't find the easy way to ensure that other processes'
      stack do *not* have the address of them. (I thought some way
      to do that, but those are very costly.)
      
      So currently, I simply boost the kprobe only when the probe
      point is already preemption disabled.
      
      > Also, the patch adds a preempt_enable() but I don't see a corresponding
      > preempt_disable().  Am I missing something?
      
      It is corresponding to the preempt_disable() in the top of
      kprobe_handler().
      I copied the code of kprobe_handler() here:
      
      static int __kprobes kprobe_handler(struct pt_regs *regs)
      {
              struct kprobe *p;
              int ret = 0;
              kprobe_opcode_t *addr = NULL;
              unsigned long *lp;
              struct kprobe_ctlblk *kcb;
      
              /*
               * We don't want to be preempted for the entire
               * duration of kprobe processing
               */
              preempt_disable();             <-- HERE
              kcb = get_kprobe_ctlblk();
      Signed-off-by: NMasami Hiramatsu <hiramatu@sdl.hitachi.co.jp>
      Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
      Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
      Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
      Cc: David S. Miller <davem@davemloft.net>
      Signed-off-by: NAndrew Morton <akpm@osdl.org>
      Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      311ac88f
  10. 25 2月, 2006 1 次提交
  11. 11 1月, 2006 3 次提交
  12. 07 11月, 2005 1 次提交
  13. 24 6月, 2005 1 次提交
    • H
      [PATCH] kprobes: function-return probes · b94cce92
      Hien Nguyen 提交于
      This patch adds function-return probes to kprobes for the i386
      architecture.  This enables you to establish a handler to be run when a
      function returns.
      
      1. API
      
      Two new functions are added to kprobes:
      
      	int register_kretprobe(struct kretprobe *rp);
      	void unregister_kretprobe(struct kretprobe *rp);
      
      2. Registration and unregistration
      
      2.1 Register
      
        To register a function-return probe, the user populates the following
        fields in a kretprobe object and calls register_kretprobe() with the
        kretprobe address as an argument:
      
        kp.addr - the function's address
      
        handler - this function is run after the ret instruction executes, but
        before control returns to the return address in the caller.
      
        maxactive - The maximum number of instances of the probed function that
        can be active concurrently.  For example, if the function is non-
        recursive and is called with a spinlock or mutex held, maxactive = 1
        should be enough.  If the function is non-recursive and can never
        relinquish the CPU (e.g., via a semaphore or preemption), NR_CPUS should
        be enough.  maxactive is used to determine how many kretprobe_instance
        objects to allocate for this particular probed function.  If maxactive <=
        0, it is set to a default value (if CONFIG_PREEMPT maxactive=max(10, 2 *
        NR_CPUS) else maxactive=NR_CPUS)
      
        For example:
      
          struct kretprobe rp;
          rp.kp.addr = /* entrypoint address */
          rp.handler = /*return probe handler */
          rp.maxactive = /* e.g., 1 or NR_CPUS or 0, see the above explanation */
          register_kretprobe(&rp);
      
        The following field may also be of interest:
      
        nmissed - Initialized to zero when the function-return probe is
        registered, and incremented every time the probed function is entered but
        there is no kretprobe_instance object available for establishing the
        function-return probe (i.e., because maxactive was set too low).
      
      2.2 Unregister
      
        To unregiter a function-return probe, the user calls
        unregister_kretprobe() with the same kretprobe object as registered
        previously.  If a probed function is running when the return probe is
        unregistered, the function will return as expected, but the handler won't
        be run.
      
      3. Limitations
      
      3.1 This patch supports only the i386 architecture, but patches for
          x86_64 and ppc64 are anticipated soon.
      
      3.2 Return probes operates by replacing the return address in the stack
          (or in a known register, such as the lr register for ppc).  This may
          cause __builtin_return_address(0), when invoked from the return-probed
          function, to return the address of the return-probes trampoline.
      
      3.3 This implementation uses the "Multiprobes at an address" feature in
          2.6.12-rc3-mm3.
      
      3.4 Due to a limitation in multi-probes, you cannot currently establish
          a return probe and a jprobe on the same function.  A patch to remove
          this limitation is being tested.
      
      This feature is required by SystemTap (http://sourceware.org/systemtap),
      and reflects ideas contributed by several SystemTap developers, including
      Will Cohen and Ananth Mavinakayanahalli.
      Signed-off-by: NHien Nguyen <hien@us.ibm.com>
      Signed-off-by: NPrasanna S Panchamukhi <prasanna@in.ibm.com>
      Signed-off-by: NFrederik Deweerdt <frederik.deweerdt@laposte.net>
      Signed-off-by: NAndrew Morton <akpm@osdl.org>
      Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      b94cce92
  14. 17 4月, 2005 1 次提交
    • L
      Linux-2.6.12-rc2 · 1da177e4
      Linus Torvalds 提交于
      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!
      1da177e4