Changes between Initial Version and Version 1 of Dev/KernelHack/COINS/worklog/201110

Timestamp:

Oct 12, 2011 12:38:06 PM (13 years ago)

Author:

mitty

Comment:

--

Dev/KernelHack/COINS/worklog/201110

@@ +1 @@
+[[PageOutline]]
+
+ = 10/12 =
+ == trace getpid() syscall with GDB ==
+ * windell57:x86_64 s0711489$ gdb
+{{{
+
+(gdb) set logging file gdb.getpid.log
+(gdb) set logging on
+Copying output to gdb.getpid.log.
+(gdb) file vmlinux
+Reading symbols from /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/vmlinux...(no debugging symbols found)...done.
+(gdb) b sys_getpid
+Breakpoint 1 at 0xffffffff81048ce4: file kernel/timer.c, line 1344.
+(gdb) target remote localhost:8864
+Remote debugging using localhost:8864
+0xffffffff810097a9 in native_safe_halt ()
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/irqflags.h:49
+49              asm volatile("sti; hlt": : :"memory");
+(gdb) c
+Continuing.
+
+Breakpoint 1, sys_getpid () at kernel/timer.c:1344
+}}}
+ * => attachment:gdb.getpid.log
+
+ * on VM guest
+  * s0711489@ubuntu-lucid64:~/coursework/KernelHack/02$ ./getpid
+{{{
+getpid() -> 2143
+}}}
+
+ == trace log with source list and print data ==
+* windell57:x86_64 s0711489$ gdb
+{{{
+
+(gdb) file vmlinux
+Reading symbols from /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/vmlinux...(no debugging symbols found)...done.
+(gdb) b sys_getpid
+Breakpoint 1 at 0xffffffff81048ce4: file kernel/timer.c, line 1344.
+(gdb) target remote localhost:8864
+Remote debugging using localhost:8864
+0xffffffff810097a9 in native_safe_halt ()
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/irqflags.h:49
+49              asm volatile("sti; hlt": : :"memory");
+(gdb) c
+Continuing.
+
+Breakpoint 1, sys_getpid () at kernel/timer.c:1344
+1344    {
+(gdb) bt
+#0  sys_getpid () at kernel/timer.c:1344
+#1  0xffffffff810029eb in ?? ()
+#2  0x0000000000000246 in ?? ()
+#3  0x00007fff70d418e0 in ?? ()
+#4  0x00007f6c11b19210 in ?? ()
+#5  0x00007f6c11b05300 in ?? ()
+#6  0x0000000000000027 in ?? ()
+#7  0x0000000000000000 in ?? ()
+(gdb) l
+1339     * which case the tgid is the same in all threads of the same group.
+1340     *
+1341     * This is SMP safe as current->tgid does not change.
+1342     */
+1343    SYSCALL_DEFINE0(getpid)
+1344    {
+1345            return task_tgid_vnr(current);
+1346    }
+1347
+1348    /*
+(gdb) s
+1345            return task_tgid_vnr(current);
+(gdb)
+get_current ()
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/current.h:14
+14              return percpu_read_stable(current_task);
+(gdb) l
+9
+10      DECLARE_PER_CPU(struct task_struct *, current_task);
+11
+12      static __always_inline struct task_struct *get_current(void)
+13      {
+14              return percpu_read_stable(current_task);
+15      }
+16
+17      #define current get_current()
+18
+(gdb) bt
+#0  get_current ()
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/current.h:14
+#1  sys_getpid () at kernel/timer.c:1345
+#2  0xffffffff810029eb in ?? ()
+#3  0x0000000000000246 in ?? ()
+#4  0x00007fff63204890 in ?? ()
+#5  0x00007fc615a98210 in ?? ()
+#6  0x00007fc615a84300 in ?? ()
+#7  0x0000000000000027 in ?? ()
+#8  0x0000000000000000 in ?? ()
+(gdb) p current_task
+Cannot access memory at address 0xb540
+(gdb) ptype current_task
+type = struct task_struct {
+
+(snip)
+
+(gdb) s
+sys_getpid () at kernel/timer.c:1344
+1344    {
+(gdb) l
+1339     * which case the tgid is the same in all threads of the same group.
+1340     *
+1341     * This is SMP safe as current->tgid does not change.
+1342     */
+1343    SYSCALL_DEFINE0(getpid)
+1344    {
+1345            return task_tgid_vnr(current);
+1346    }
+1347
+1348    /*
+(gdb) bt
+#0  sys_getpid () at kernel/timer.c:1344
+#1  0xffffffff810029eb in ?? ()
+#2  0x0000000000000246 in ?? ()
+#3  0x00007fff63204890 in ?? ()
+#4  0x00007fc615a98210 in ?? ()
+#5  0x00007fc615a84300 in ?? ()
+#6  0x0000000000000027 in ?? ()
+#7  0x0000000000000000 in ?? ()
+(gdb) s
+1345            return task_tgid_vnr(current);
+(gdb) s
+task_tgid_vnr (tsk=0xffff88001bbe5880) at include/linux/sched.h:1606
+1606    {
+(gdb) l
+1601    }
+1602
+1603    pid_t task_tgid_nr_ns(struct task_struct *tsk, struct pid_namespace *ns);
+1604
+1605    static inline pid_t task_tgid_vnr(struct task_struct *tsk)
+1606    {
+1607            return pid_vnr(task_tgid(tsk));
+1608    }
+1609
+1610
+(gdb) bt
+#0  task_tgid_vnr (tsk=0xffff88001bbe5880) at include/linux/sched.h:1606
+#1  0xffffffff81048cf6 in sys_getpid () at kernel/timer.c:1345
+#2  0xffffffff810029eb in ?? ()
+#3  0x0000000000000246 in ?? ()
+#4  0x00007fff63204890 in ?? ()
+#5  0x00007fc615a98210 in ?? ()
+#6  0x00007fc615a84300 in ?? ()
+#7  0x0000000000000027 in ?? ()
+#8  0x0000000000000000 in ?? ()
+(gdb) p tsk
+$2 = (struct task_struct *) 0xffff88001bbe5880
+(gdb) ptype tsk
+type = struct task_struct {
+
+(snip)
+
+    pid_t pid;
+    pid_t tgid;
+
+(snip)
+
+    struct task_struct *group_leader;
+    struct list_head ptraced;
+    struct list_head ptrace_entry;
+    struct pid_link pids[3];
+
+(snip)
+
+(gdb) ptype tsk->group_leader->pids
+type = struct pid_link {
+    struct hlist_node node;
+    struct pid *pid;
+} [3]
+
+(snip)
+
+(gdb) s
+1607            return pid_vnr(task_tgid(tsk));
+(gdb)
+1606    {
+(gdb)
+1607            return pid_vnr(task_tgid(tsk));
+(gdb)
+pid_vnr (pid=0xffff88001fb55400) at kernel/pid.c:444
+444     {
+(gdb) bt
+#0  pid_vnr (pid=0xffff88001fb55400) at kernel/pid.c:444
+#1  0xffffffff81048783 in task_tgid_vnr (tsk=<value optimized out>)
+    at include/linux/sched.h:1607
+#2  0xffffffff81048cf6 in sys_getpid () at kernel/timer.c:1345
+#3  0xffffffff810029eb in ?? ()
+#4  0x0000000000000246 in ?? ()
+#5  0x00007fff63204890 in ?? ()
+#6  0x00007fc615a98210 in ?? ()
+#7  0x00007fc615a84300 in ?? ()
+#8  0x0000000000000027 in ?? ()
+#9  0x0000000000000000 in ?? ()
+(gdb) l
+439             }
+440             return nr;
+441     }
+442
+443     pid_t pid_vnr(struct pid *pid)
+444     {
+445             return pid_nr_ns(pid, current->nsproxy->pid_ns);
+446     }
+447     EXPORT_SYMBOL_GPL(pid_vnr);
+448
+(gdb) ptype pid
+type = struct pid {
+    atomic_t count;
+    unsigned int level;
+    struct hlist_head tasks[3];
+    struct rcu_head rcu;
+    struct upid numbers[1];
+} *
+(gdb) up
+#1  0xffffffff81048783 in task_tgid_vnr (tsk=<value optimized out>)
+    at include/linux/sched.h:1607
+1607            return pid_vnr(task_tgid(tsk));
+(gdb) ptype tsk->nsproxy->pid_ns
+type = struct pid_namespace {
+    struct kref kref;
+    struct pidmap pidmap[128];
+    int last_pid;
+    struct task_struct *child_reaper;
+    struct kmem_cache *pid_cachep;
+    unsigned int level;
+    struct pid_namespace *parent;
+    struct vfsmount *proc_mnt;
+    struct bsd_acct_struct *bacct;
+} *
+(gdb) down
+#0  pid_vnr (pid=0xffff88001fb55400) at kernel/pid.c:444
+444     {
+(gdb) s
+445             return pid_nr_ns(pid, current->nsproxy->pid_ns);
+(gdb)
+get_current (pid=0xffff88001fb55400)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/current.h:14
+14              return percpu_read_stable(current_task);
+(gdb) p current_task
+Cannot access memory at address 0xb540
+(gdb) s
+pid_vnr (pid=0xffff88001fb55400) at kernel/pid.c:445
+445             return pid_nr_ns(pid, current->nsproxy->pid_ns);
+(gdb) s
+444     {
+(gdb)
+445             return pid_nr_ns(pid, current->nsproxy->pid_ns);
+(gdb)
+pid_nr_ns (pid=0xffff88001fb55400, ns=0xffffffff8181bfe0) at kernel/pid.c:431
+431     {
+(gdb) bt
+#0  pid_nr_ns (pid=0xffff88001fb55400, ns=0xffffffff8181bfe0)
+    at kernel/pid.c:431
+#1  0xffffffff81052db6 in pid_vnr (pid=0xffff88001fb55400) at kernel/pid.c:445
+#2  0xffffffff81048783 in task_tgid_vnr (tsk=<value optimized out>)
+    at include/linux/sched.h:1607
+#3  0xffffffff81048cf6 in sys_getpid () at kernel/timer.c:1345
+#4  0xffffffff810029eb in ?? ()
+#5  0x0000000000000246 in ?? ()
+#6  0x00007fff63204890 in ?? ()
+#7  0x00007fc615a98210 in ?? ()
+#8  0x00007fc615a84300 in ?? ()
+#9  0x0000000000000027 in ?? ()
+#10 0x0000000000000000 in ?? ()
+(gdb) l
+426             return pid;
+427     }
+428     EXPORT_SYMBOL_GPL(find_get_pid);
+429
+430     pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
+431     {
+432             struct upid *upid;
+433             pid_t nr = 0;
+434
+435             if (pid && ns->level <= pid->level) {
+(gdb) l
+436                     upid = &pid->numbers[ns->level];
+437                     if (upid->ns == ns)
+438                             nr = upid->nr;
+439             }
+440             return nr;
+441     }
+442
+443     pid_t pid_vnr(struct pid *pid)
+444     {
+445             return pid_nr_ns(pid, current->nsproxy->pid_ns);
+(gdb) ptype pid
+type = struct pid {
+    atomic_t count;
+    unsigned int level;
+    struct hlist_head tasks[3];
+    struct rcu_head rcu;
+    struct upid numbers[1];
+} *
+(gdb) ptype ns
+type = struct pid_namespace {
+    struct kref kref;
+    struct pidmap pidmap[128];
+    int last_pid;
+    struct task_struct *child_reaper;
+    struct kmem_cache *pid_cachep;
+    unsigned int level;
+    struct pid_namespace *parent;
+    struct vfsmount *proc_mnt;
+    struct bsd_acct_struct *bacct;
+} *
+type = struct upid {
+    int nr;
+    struct pid_namespace *ns;
+    struct hlist_node pid_chain;
+} *
+(gdb) ptype pid_t
+type = int
+(gdb) p ns->level
+$5 = 0
+(gdb) p pid->level
+$6 = 0
+(gdb) p ns->level <= pid->level
+$7 = 1
+(gdb) p ns
+$8 = (struct pid_namespace *) 0xffffffff8181bfe0
+(gdb) p &pid->numbers[ns->level]
+$9 = (struct upid *) 0xffff88001fb55430
+(gdb) p (&pid->numbers[ns->level])->ns
+$10 = (struct pid_namespace *) 0xffffffff8181bfe0
+(gdb) info locals
+upid = <value optimized out>
+nr = <value optimized out>
+(gdb) p nr
+$11 = <value optimized out>
+(gdb) p (&pid->numbers[ns->level])->nr
+$12 = 2225
+(gdb) s
+435             if (pid && ns->level <= pid->level) {
+(gdb)
+431     {
+(gdb)
+435             if (pid && ns->level <= pid->level) {
+(gdb)
+436                     upid = &pid->numbers[ns->level];
+(gdb)
+437                     if (upid->ns == ns)
+(gdb) p upid
+$13 = (struct upid *) 0xffff88001fb55430
+(gdb) s
+438                             nr = upid->nr;
+(gdb) p upid->ns == ns
+$14 = 1
+(gdb) p nr
+$15 = <value optimized out>
+(gdb) p upid->nr
+$16 = 2225
+(gdb) s
+441     }
+(gdb)
+pid_vnr (pid=<value optimized out>) at kernel/pid.c:446
+446     }
+(gdb) s
+task_tgid_vnr (tsk=<value optimized out>) at include/linux/sched.h:1608
+1608    }
+(gdb)
+sys_getpid () at kernel/timer.c:1346
+1346    }
+(gdb)
+sys_getpid () at kernel/timer.c:1345
+1345            return task_tgid_vnr(current);
+(gdb)
+sys_getpid () at kernel/timer.c:1346
+1346    }
+(gdb)
+}}}
+
+ * on VM guest
+  * s0711489@ubuntu-lucid64:~/coursework/KernelHack/02$ ./getpid
+{{{
+getpid() -> 2225
+}}}
+
+ === location of functions on source file ===
+ * windell57:x86_64 s0711489$ grep percpu_read_stable -r .
+{{{
+(snip)
+
+./arch/x86/include/asm/percpu.h:#define percpu_read_stable(var)         percpu_from_op("mov", var, "p" (&(var)))
+
+(snip)
+}}}
+
+ * windell57:x86_64 s0711489$ grep task_tgid -r .
+{{{
+(snip)
+
+./include/linux/sched.h:static inline struct pid *task_tgid(struct task_struct *task)
+
+(snip)
+}}}
+
+ * include/linux/sched.h
+{{{
+static inline struct pid *task_tgid(struct task_struct *task)
+{
+        return task->group_leader->pids[PIDTYPE_PID].pid;
+}
+}}}
+
+ === get_current function ===
+ * windell57:02 s0711489$ gcc -E ../linux-2.6.35.14/x86_64/arch/x86/include/asm/current.h -I ~/coursework/KernelHack/linux-2.6.35.14/x86_64/include -I ~/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/ > current.h
+{{{
+In file included from /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/percpu.h:44,
+                 from ../linux-2.6.35.14/x86_64/arch/x86/include/asm/current.h:5:
+/home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/include/linux/kernel.h:733:2: warning: #warning Attempt to use kernel headers from user space, see http:
+}}}
+ * pre-processed arch/x86/include/asm/current.h
+{{{
+static __always_inline struct task_struct *get_current(void)
+{
+ return ({ typeof(current_task) pfo_ret__; switch (sizeof(current_task)) { case 1: asm("mov" "b ""%P" "1"",%0" : "=q" (pfo_ret__) : "p" (&(current_task))); break; case 2: asm("mov" "w ""%P" "1"",%0" : "=r" (pfo_ret__) : "p" (&(current_task))); break; case 4: asm("mov" "l ""%P" "1"",%0" : "=r" (pfo_ret__) : "p" (&(current_task))); break; case 8: asm("mov" "q ""%P" "1"",%0" : "=r" (pfo_ret__) : "p" (&(current_task))); break; default: __bad_percpu_size(); } pfo_ret__; });
+}
+}}}