kcore: add _text to KCORE_TEXT
Wu Fengguang [Wed, 26 May 2010 21:43:27 +0000 (14:43 -0700)]
Extend KCORE_TEXT to cover the pages between _text and _stext, to allow
examining some important page table pages.

`readelf -a` output on x86_64 before and after patch:
  Type           Offset             VirtAddr           PhysAddr
before    LOAD           0x00007fff8100c000 0xffffffff81009000 0x0000000000000000
after     LOAD           0x00007fff81003000 0xffffffff81000000 0x0000000000000000

The newly covered pages are:

0xffffffff81000000 <startup_64> etc.
0xffffffff81001000 <init_level4_pgt>
0xffffffff81002000 <level3_ident_pgt>
0xffffffff81003000 <level3_kernel_pgt>
0xffffffff81004000 <level2_fixmap_pgt>
0xffffffff81005000 <level1_fixmap_pgt>
0xffffffff81006000 <level2_ident_pgt>
0xffffffff81007000 <level2_kernel_pgt>
0xffffffff81008000 <level2_spare_pgt>

Before patch, /proc/kcore shows outdated contents for the above page
table pages, for example:

(gdb) p level3_ident_pgt
$1 = {<text variable, no debug info>} 0xffffffff81002000 <level3_ident_pgt>
(gdb) p/x *((pud_t *)&level3_ident_pgt)@512
$2 = {{pud = 0x1006063}, {pud = 0x0} <repeats 511 times>}

while the real content is:

root@hp /home/wfg# hexdump -s 0x1002000 -n 4096 /dev/mem
1002000 6063 0100 0000 0000 8067 0000 0000 0000
1002010 0000 0000 0000 0000 0000 0000 0000 0000
*
1003000

That is, on a x86_64 box with 2GB memory, we can see first-1GB / full-2GB
identity mapping before/after patch:

(gdb) p/x *((pud_t *)&level3_ident_pgt)@512
before  $1 = {{pud = 0x1006063}, {pud = 0x0} <repeats 511 times>}
after   $1 = {{pud = 0x1006063}, {pud = 0x8067}, {pud = 0x0} <repeats 510 times>}

Obviously the content before patch is wrong.

Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/kcore.c

index c837a77..6f37c39 100644 (file)
@@ -588,7 +588,7 @@ static struct kcore_list kcore_text;
  */
 static void __init proc_kcore_text_init(void)
 {
-       kclist_add(&kcore_text, _stext, _end - _stext, KCORE_TEXT);
+       kclist_add(&kcore_text, _text, _end - _text, KCORE_TEXT);
 }
 #else
 static void __init proc_kcore_text_init(void)