Changes between Version 12 and Version 13 of Dev/KernelHack/COINS/worklog/201111

Timestamp:

Nov 25, 2011 2:26:06 AM (12 years ago)

Author:

mitty

Comment:

--

Dev/KernelHack/COINS/worklog/201111

@@ -2822 +2822 @@
 Continuing.
 }}}
+
+ === use pointer of DATA ===
+ * s0711489@ubuntu-lucid64:~$ sudo insmod stackmod.ko entry=4
+ * s0711489@ubuntu-lucid64:~$ sudo mknod /dev/stack c 251 0
+ * s0711489@ubuntu-lucid64:~$ sudo chmod 666 /dev/stack
+
+ * s0711489@ubuntu-lucid64:~$ cat /sys/module/stackmod/sections/.text
+{{{
+0xffffffffa0056000
+}}}
+ * s0711489@ubuntu-lucid64:~$ cat /sys/module/stackmod/sections/.data
+{{{
+0xffffffffa0056718
+}}}
+ * s0711489@ubuntu-lucid64:~$ cat /sys/module/stackmod/sections/.bss
+{{{
+0xffffffffa0056950
+}}}
+
+ * 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) add-symbol-file ../../04/stackmod/stackmod.o 0xffffffffa0056000 -s .data 0xffffffffa0056718 -s .bss 0xffffffffa0056950
+add symbol table from file "../../04/stackmod/stackmod.o" at
+        .text_addr = 0xffffffffa0056000
+        .data_addr = 0xffffffffa0056718
+        .bss_addr = 0xffffffffa0056950
+(y or n) y
+Reading symbols from /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.o...done.
+(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) b stackmod_read
+Breakpoint 1 at 0xffffffffa00560b4: file /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c, line 62.
+(gdb) b stackmod_write
+Breakpoint 2 at 0xffffffffa0056207: file /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c, line 105.
+(gdb) b stackmod_proc_read
+Breakpoint 3 at 0xffffffffa00561ca: file /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c, line 153.
+(gdb) c
+Continuing.
+}}}
+
+ * s0711489@ubuntu-lucid64:~$ cat /proc/stackmod
+{{{
+stack: 0
+}}}
+{{{
+Breakpoint 3, stackmod_proc_read (page=0xffff880019958000 "`\204\225\031",
+    start=0xffff88001ac77e90, off=0, count=3072, eof=0xffff88001ac77e9c,
+    data=0x0)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:153
+153     ) {
+(gdb) p stack
+$1 = {data = 0xffff88001aca6d40, depth = 0, errno = 0}
+(gdb) p stack p
+A syntax error in expression, near `p'.
+(gdb) p p
+No symbol "p" in current context.
+(gdb) p stack.data
+$2 = (DATA *) 0xffff88001aca6d40
+(gdb) p stack.data[0]
+$3 = {length = 449474496, content = 0xffff88001aca6c88 "\210l\312\032"}
+(gdb) p stack.data[1]
+$4 = {length = 0, content = 0x0}
+(gdb) p stack.data[2]
+$5 = {length = 0,
+  content = 0x2e2e02020010e071 <Address 0x2e2e02020010e071 out of bounds>}
+(gdb) p stack.data[3]
+$6 = {length = 0, content = 0x0}
+(gdb) p stack.data[4]
+$7 = {length = 0, content = 0xffff88001dfc94b0 "h\n\235\037"}
+(gdb) c
+Continuing.
+
+Breakpoint 3, stackmod_proc_read (page=0xffff880019958000 "stack: 0\n",
+    start=0xffff88001ac77e90, off=9, count=3072, eof=0xffff88001ac77e9c,
+    data=0x0)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:153
+153     ) {
+(gdb) p eof
+$8 = (int *) 0xffff88001ac77e9c
+(gdb) p *eof
+$9 = 0
+(gdb) c
+Continuing.
+}}}
+
+ * s0711489@ubuntu-lucid64:~$ echo depth0 > /dev/stack
+{{{
+Breakpoint 2, stackmod_write (filep=0xffff88001b793900,
+    buf_user=0x2262c08 "depth0\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>..., size=7,
+    offset=0xffff88001ac19f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:105
+105     ) {
+(gdb) p p
+$10 = <value optimized out>
+(gdb) n
+108             printk(KERN_DEBUG MODNAME " is written\n");
+(gdb)
+105     ) {
+(gdb)
+108             printk(KERN_DEBUG MODNAME " is written\n");
+(gdb)
+110             if (size == 0) {
+(gdb)
+113             if (stack.depth >= entry) {
+(gdb)
+117             if (buf_user == NULL) {
+(gdb)
+121             p = stack.data + stack.depth;
+(gdb) p stack
+$11 = {data = 0xffff88001aca6d40, depth = 0, errno = 0}
+(gdb) p stack.data
+$12 = (DATA *) 0xffff88001aca6d40
+(gdb) p stack.data[0]
+$13 = {length = 449474496, content = 0xffff88001aca6c88 "\210l\312\032"}
+(gdb) p stack.data[1]
+$14 = {length = 0, content = 0x0}
+(gdb) n
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb)
+121             p = stack.data + stack.depth;
+(gdb)
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb) p p
+$15 = (DATA *) 0xffff88001aca6d40
+(gdb) ptype p
+type = struct kernel_module_stack_data {
+    int length;
+    char *content;
+} *
+(gdb) p *p
+$16 = {length = 449474496, content = 0xffff88001aca6c88 "\210l\312\032"}
+(gdb) n
+123             if (p->content == NULL) {
+(gdb) n
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb) p *p
+$17 = {length = 449474496, content = 0xffff88001aca6c88 "\210l\312\032"}
+(gdb) n
+123             if (p->content == NULL) {
+(gdb)
+127             p->length = size;
+(gdb) p *p
+$18 = {length = 449474496, content = 0xffff88001dfc94c8 "\030\225\374\035"}
+(gdb) p size
+$19 = 7
+(gdb) n
+129             if (copy_from_user(p->content, buf_user, size) != 0) {
+(gdb) p *p
+$20 = {length = 7, content = 0xffff88001dfc94c8 "\030\225\374\035"}
+(gdb) n
+136             stack.depth++;
+(gdb) p *p
+$21 = {length = 7, content = 0xffff88001dfc94c8 "depth0\n\377holders"}
+(gdb) p stack
+$22 = {data = 0xffff88001aca6d40, depth = 0, errno = 0}
+(gdb) n
+140             return size;
+(gdb) p size
+$23 = 0
+(gdb) n
+138             *offset += size;
+(gdb)
+141     }
+(gdb) p size
+$24 = <value optimized out>
+(gdb) n
+vfs_write (file=0xffff88001b793900,
+    buf=0x2262c08 "depth0\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>...,
+    count=<value optimized out>, pos=0xffff88001ac19f48) at fs/read_write.c:369
+369                     if (ret > 0) {
+(gdb) finish
+Run till exit from #0  vfs_write (file=0xffff88001b793900,
+    buf=0x2262c08 "depth0\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>...,
+    count=<value optimized out>, pos=0xffff88001ac19f48) at fs/read_write.c:369
+0xffffffff810df6b7 in sys_write (fd=<value optimized out>,
+    buf=0x2262c08 "depth0\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>..., count=7)
+    at fs/read_write.c:418
+418                     ret = vfs_write(file, buf, count, &pos);
+Could not fetch register "orig_rax"; remote failure reply 'E00'
+(gdb) c
+Continuing.
+}}}
+
+ * s0711489@ubuntu-lucid64:~$ echo depth1 > /dev/stack
+{{{
+Breakpoint 2, stackmod_write (filep=0xffff88001b906480,
+    buf_user=0x2262c08 "depth1\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>..., size=7,
+    offset=0xffff88001ac19f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:105
+105     ) {
+(gdb) n
+108             printk(KERN_DEBUG MODNAME " is written\n");
+(gdb)
+105     ) {
+(gdb)
+108             printk(KERN_DEBUG MODNAME " is written\n");
+(gdb)
+110             if (size == 0) {
+(gdb)
+113             if (stack.depth >= entry) {
+(gdb)
+117             if (buf_user == NULL) {
+(gdb)
+121             p = stack.data + stack.depth;
+(gdb)
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb)
+121             p = stack.data + stack.depth;
+(gdb)
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb)
+123             if (p->content == NULL) {
+(gdb)
+122             p->content = (char *) kmalloc(size * sizeof(char), GFP_KERNEL);
+(gdb)
+123             if (p->content == NULL) {
+(gdb)
+127             p->length = size;
+(gdb)
+129             if (copy_from_user(p->content, buf_user, size) != 0) {
+(gdb) p size
+$25 = 7
+(gdb) p p
+$26 = (DATA *) 0xffff88001aca6d50
+(gdb) p *p
+$27 = {length = 7, content = 0xffff88001dfc9518 " \225\374\035"}
+(gdb) p stack
+$28 = {data = 0xffff88001aca6d40, depth = 1, errno = 0}
+(gdb) s
+copy_from_user (filep=<value optimized out>,
+    buf_user=0x2262c08 "depth1\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>..., size=7,
+    offset=0xffff88001ac19f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/uaccess_64.h:53
+53              might_fault();
+(gdb) finish
+Run till exit from #0  copy_from_user (filep=<value optimized out>,
+    buf_user=0x2262c08 "depth1\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>..., size=7,
+    offset=0xffff88001ac19f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/linux-2.6.35.14/x86_64/arch/x86/include/asm/uaccess_64.h:53
+129             if (copy_from_user(p->content, buf_user, size) != 0) {
+(gdb) p size
+$29 = 7
+(gdb) n
+136             stack.depth++;
+(gdb)
+140             return size;
+(gdb) p size
+$30 = 0
+(gdb) n
+138             *offset += size;
+(gdb) p *offset
+$31 = 0
+(gdb) n
+141     }
+(gdb) p *offset
+$32 = 7
+(gdb) p size
+$33 = <value optimized out>
+(gdb) finish
+Run till exit from #0  stackmod_write (filep=<value optimized out>,
+    buf_user=0x2262c08 "depth1\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>...,
+    size=<value optimized out>, offset=0xffff88001ac19f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:141
+0xffffffff810df5a3 in vfs_write (file=0xffff88001b906480,
+    buf=0x2262c08 "depth1\ne -o filenames -F _insmod insmod\nalternatives\n\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337\337", <incomplete sequence \337>...,
+    count=<value optimized out>, pos=0xffff88001ac19f48) at fs/read_write.c:366
+366                             ret = file->f_op->write(file, buf, count, pos);
+Could not fetch register "orig_rax"; remote failure reply 'E00'
+(gdb) c
+Continuing.
+}}}
+
+ * s0711489@ubuntu-lucid64:~$ cat /proc/stackmod
+{{{
+stack: 2
+}}}
+{{{
+Breakpoint 3, stackmod_proc_read (page=0xffff880019958000 "stack: 0\n",
+    start=0xffff88001b885e90, off=0, count=3072, eof=0xffff88001b885e9c,
+    data=0x0)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:153
+153     ) {
+(gdb) p stack
+$34 = {data = 0xffff88001aca6d40, depth = 2, errno = 0}
+(gdb) p stack.data
+$35 = (DATA *) 0xffff88001aca6d40
+(gdb) p stack.data[0]
+$36 = {length = 7, content = 0xffff88001dfc94c8 "depth0\n\377holders"}
+(gdb) p stack.data[1]
+$37 = {length = 7, content = 0xffff88001dfc9518 "depth1\n\377(\225\374\035"}
+(gdb) p stack.data[2]
+$38 = {length = 0,
+  content = 0x2e2e02020010e071 <Address 0x2e2e02020010e071 out of bounds>}
+(gdb) p stack.data[3]
+$39 = {length = 0, content = 0x0}
+(gdb) p stack.data[4]
+$40 = {length = 0, content = 0xffff88001dfc94b0 "h\n\235\037"}
+(gdb) p stack.data[5]
+$41 = {length = 1, content = 0x0}
+(gdb) n
+156             outlen = sprintf(page, "stack: %d\n", stack.depth);
+(gdb)
+153     ) {
+(gdb)
+156             outlen = sprintf(page, "stack: %d\n", stack.depth);
+(gdb) p outlen
+$42 = <value optimized out>
+(gdb) n
+157             *eof = 1;
+(gdb) p outlen
+$43 = <value optimized out>
+(gdb) n
+156             outlen = sprintf(page, "stack: %d\n", stack.depth);
+(gdb)
+159             printk(KERN_DEBUG "/proc/" PROCNAME " is read\n");
+(gdb) p outlen
+$44 = <value optimized out>
+(gdb) n
+162     }
+(gdb) p outlen
+$45 = <value optimized out>
+(gdb) finish
+Run till exit from #0  stackmod_proc_read (page=<value optimized out>,
+    start=<value optimized out>, off=<value optimized out>,
+    count=<value optimized out>, eof=0xffff88001b885e9c,
+    data=<value optimized out>)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:162
+__proc_file_read (file=<value optimized out>,
+    buf=0xfb6000 <Address 0xfb6000 out of bounds>, nbytes=32768,
+    ppos=0xffff88001b885f48) at fs/proc/generic.c:125
+125                     if (n == 0)   /* end of file */
+Could not fetch register "orig_rax"; remote failure reply 'E00'
+(gdb) c
+Continuing.
+
+Breakpoint 3, stackmod_proc_read (page=0xffff880019958000 "stack: 2\n",
+    start=0xffff88001b885e90, off=9, count=3072, eof=0xffff88001b885e9c,
+    data=0x0)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:153
+153     ) {
+(gdb) c
+Continuing.
+}}}
+
+
+ * s0711489@ubuntu-lucid64:~$ cat /dev/stack
+{{{
+depth1
+depth0
+}}}
+{{{
+Breakpoint 1, stackmod_read (filep=0xffff88001b591180,
+    buf_user=0xcec000 <Address 0xcec000 out of bounds>, size=32768,
+    offset=0xffff88001ba91f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:62
+62      ) {
+(gdb) p stack
+$46 = {data = 0xffff88001aca6d40, depth = 2, errno = 0}
+(gdb) n
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+62      ) {
+(gdb)
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+68              if (size == 0) {
+(gdb)
+71              if (stack.depth == 0) {
+(gdb)
+75              if (buf_user == NULL) {
+(gdb)
+78              if (! access_ok(VERIFY_WRITE, buf_user, size) ) {
+(gdb)
+82              stack.depth--;
+(gdb)
+83              p = stack.data + stack.depth;
+(gdb)
+82              stack.depth--;
+(gdb)
+83              p = stack.data + stack.depth;
+(gdb)
+85              len = p->length;
+(gdb) p p
+$47 = (DATA *) 0xffff88001aca6d50
+(gdb) p stack.data
+$48 = (DATA *) 0xffff88001aca6d40
+(gdb) p stack.data[0]
+$49 = {length = 7, content = 0xffff88001dfc94c8 "depth0\n\377holders"}
+(gdb) p stack.data[1]
+$50 = {length = 7, content = 0xffff88001dfc9518 "depth1\n\377(\225\374\035"}
+(gdb) n
+86              if (size < len) {
+(gdb) p len
+$51 = 7
+(gdb) n
+87                      len = size;
+(gdb)
+89              if (len > 0 && copy_to_user(buf_user, p->content, len) != 0) {
+(gdb) p len
+$52 = 7
+(gdb) n
+94              kfree(p->content);
+(gdb) p p
+$53 = (DATA *) 0xffff88001aca6d50
+(gdb) p *p
+$54 = {length = 7, content = 0xffff88001dfc9518 "depth1\n\377(\225\374\035"}
+(gdb) n
+98              *offset += len;
+(gdb) p *p
+$55 = {length = 7, content = 0xffff88001dfc9518 " \225\374\035"}
+(gdb) n
+95              p->content = NULL;
+(gdb)
+96              p->length = 0;
+(gdb)
+98              *offset += len;
+(gdb) p len
+$56 = 7
+(gdb) p *p
+$57 = {length = 0, content = 0x0}
+(gdb) n
+100             return len;
+(gdb)
+101     }
+(gdb) c
+Continuing.
+
+Breakpoint 1, stackmod_read (filep=0xffff88001b591180,
+    buf_user=0xcec000 "depth1\n", size=32768, offset=0xffff88001ba91f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:62
+62      ) {
+(gdb) n
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+62      ) {
+(gdb)
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+68              if (size == 0) {
+(gdb)
+71              if (stack.depth == 0) {
+(gdb) p stack
+$58 = {data = 0xffff88001aca6d40, depth = 1, errno = 0}
+(gdb) n
+75              if (buf_user == NULL) {
+(gdb)
+78              if (! access_ok(VERIFY_WRITE, buf_user, size) ) {
+(gdb)
+82              stack.depth--;
+(gdb)
+83              p = stack.data + stack.depth;
+(gdb)
+82              stack.depth--;
+(gdb)
+83              p = stack.data + stack.depth;
+(gdb)
+85              len = p->length;
+(gdb) p *p
+$59 = {length = 7, content = 0xffff88001dfc94c8 "depth0\n\377holders"}
+(gdb) n
+86              if (size < len) {
+(gdb)
+87                      len = size;
+(gdb)
+89              if (len > 0 && copy_to_user(buf_user, p->content, len) != 0) {
+(gdb) p len
+$60 = 7
+(gdb) n
+94              kfree(p->content);
+(gdb) n
+98              *offset += len;
+(gdb)
+95              p->content = NULL;
+(gdb)
+96              p->length = 0;
+(gdb)
+98              *offset += len;
+(gdb) p *p
+$61 = {length = 0, content = 0x0}
+(gdb) n
+100             return len;
+(gdb) p buf_user
+$62 = 0xcec000 "depth0\n"
+(gdb) n
+101     }
+(gdb) c
+Continuing.
+
+Breakpoint 1, stackmod_read (filep=0xffff88001b591180,
+    buf_user=0xcec000 "depth0\n", size=32768, offset=0xffff88001ba91f48)
+    at /home/ugrad/07/s0711489/coursework/KernelHack/04/stackmod/stackmod.c:62
+62      ) {
+(gdb) n
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+62      ) {
+(gdb)
+66              printk(KERN_DEBUG MODNAME " is read\n");
+(gdb)
+68              if (size == 0) {
+(gdb) p stack
+$63 = {data = 0xffff88001aca6d40, depth = 0, errno = 0}
+(gdb) p stack.data[0]
+$64 = {length = 0, content = 0x0}
+(gdb) n
+71              if (stack.depth == 0) {
+(gdb)
+101     }
+(gdb) c
+Continuing.
+}}}