问题
While dumping heap of a win32 processes (Mostly in process which has high heap memory consumption like IE ) using !heap -a 004e0000 I find multiple segments of a particular heap like ,
Heap entries for Segment00 in Heap 004e0000
Heap entries for Segment01 in Heap 004e0000
Heap entries for Segment02 in Heap 004e0000
My questions are
Question 1. Why its necessory to divide single heap into multiple segments ?
Question 2. Most of the times I find a large gap between two segments. For example in below image Segment00 actually ends @ 0x005e0000 (Where un-commited bytes started) and Segment01 getting started @ 0x05b60000.
Why this gap ?? Couldn't we use the same segment (Segment00)for further allocation ??
Question 3. How can I find the number of segments present in particular heap and their addresses from process memory memory or more specifically heap offset (example heap_handle+0xsomeoffset ?
回答1:
As an answer to Question 3, I think, I've found a "hacky" way to get the segment base address from memory.
0:027> !heap
Index Address Name Debugging options enabled
1: 00790000
2: 004d0000
3: 028b0000
4: 02a40000
5: 02fa0000
6: 03b00000
7: 02ca0000
8: 03ac0000
9: 04d80000
10: 0a850000
We take heap 0x00790000 and list all Segments in it.
0:027> !heap 00790000
Index Address Name Debugging options enabled
1: 00790000
Segment at 00790000 to 00890000 (00100000 bytes committed)
Segment at 053a0000 to 054a0000 (00100000 bytes committed)
Segment at 05d40000 to 05f40000 (00200000 bytes committed)
Segment at 063e0000 to 067e0000 (00400000 bytes committed)
Segment at 09ce0000 to 0a4e0000 (007fa000 bytes committed)
Now its time to get the same Segment base addresses manually from memory.
0:027> dt _HEAP 00790000
ntdll!_HEAP
+0x000 Entry : _HEAP_ENTRY
+0x008 SegmentSignature : 0xffeeffee
+0x00c SegmentFlags : 0
+0x010 SegmentListEntry : _LIST_ENTRY [ 0x53a0010 - 0x7900a8 ]
+0x018 Heap : 0x00790000 _HEAP
+0x01c BaseAddress : 0x00790000 Void
..
..
We are interested in SegmentListEntry (Which is @ offset 0x010)
We dump 2 DWORD from address heap_base + 0x10
0:027> dd 00790000 + 0x10 L2
00790010 053a0010 007900a8
Then we take the BLINK (which means the 2nd DWORD of above output, which is 0x007900a8) and dump 2 DWROD from there. And we keep doing it until we reach the same pointer from where we started, which is 0x007900a8
0:027> dd 007900a8 L2
007900a8 00790010 09ce0010
0:027> dd 09ce0010 L2
09ce0010 007900a8 063e0010
0:027> dd 063e0010 L2
063e0010 09ce0010 05d40010
0:027> dd 05d40010 L2
05d40010 063e0010 053a0010
0:027> dd 053a0010 L2
053a0010 05d40010 00790010
0:027> dd 00790010 L2
00790010 053a0010 007900a8
Since we reached the same point from where we started, we can stop here.
0:027> dd 007900a8 L2
007900a8 00790010 09ce0010
Now take a look at the values we got above. If you subtract 16 from all (except 0x007900a8 and 0x007900a8)them you will get Segment Base addresses.
0:027> ? 09ce0000 + 16
Evaluate expression: 164495382 = 09ce0016
Which are
00790000
053a0000
05d40000
063e0000
09ce0000
来源：https://stackoverflow.com/questions/28524619/process-heap-segments-and-their-necessity