This patch is a rewrite of libc.debug.malloc = 10 (chk_malloc). It provides
the same features as the original (poison freed memory, detect heap overruns
and underruns), except that it provides more debugging information whenever it
detects a problem.
In addition to the original features, the new chk_malloc() implementation
detects multiple frees within a given range of the last N allocations, N being
configurable via the system property libc.debug.malloc.backlog.
Finally, this patch keeps track of all outstanding memory allocations. On
program exit, we walk that list and report each outstanding allocation.
(There is support (not enabled) for a scanner thread periodically walks over
the list of outstanding allocations as well as the backlog of recently-freed
allocations, checking for heap-usage errors.)
Feature overview:
1) memory leaks
2) multiple frees
3) use after free
4) overrun
Implementation:
-- for each allocation, there is a:
1) stack trace at the time the allocation is made
2) if the memory is freed, there is also a stack trace at the point
3) a front and rear guard (fence)
4) the stack traces are kept together with the allocation
-- the following lists and maintained
1) all outstanding memory allocations
3) a backlog of allocations what are freed; when you call free(), instead of
actually freed, the allocation is moved to this backlog;
4) when the backlog of allocations gets full, the oldest entry gets evicted
from it; at that point, the allocation is checked for overruns or
use-after-free errors, and then actually freed.
5) when the program exits, the list of outstanding allocations and the
backlog are inspected for errors, then freed;
To use this, set the following system properties before running the process or
processes you want to inspect:
libc.malloc.debug.backlog # defaults to 100
libc.malloc.debug 10
When a problem is detected, you will see the following on logcat for a multiple
free:
E/libc ( 7233): +++ ALLOCATION 0x404b9278 SIZE 10 BYTES MULTIPLY FREED!
E/libc ( 7233): +++ ALLOCATION 0x404b9278 SIZE 10 ALLOCATED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c658 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d80 /system/lib/libc.so
E/libc ( 7233): #03 pc 4009647c /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
E/libc ( 7233): +++ ALLOCATION 0x404b9278 SIZE 10 FIRST FREED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c7d2 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d94 /system/lib/libc.so
E/libc ( 7233): #03 pc 40096490 /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
E/libc ( 7233): +++ ALLOCATION 0x404b9278 SIZE 10 NOW BEING FREED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c6ac /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d94 /system/lib/libc.so
E/libc ( 7233): #03 pc 400964a0 /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
The following for a heap overrun and underrun:
E/libc ( 7233): +++ REAR GUARD MISMATCH [10, 11)
E/libc ( 7233): +++ ALLOCATION 0x404b9198 SIZE 10 HAS A CORRUPTED REAR GUARD
E/libc ( 7233): +++ ALLOCATION 0x404b9198 SIZE 10 ALLOCATED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c658 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d80 /system/lib/libc.so
E/libc ( 7233): #03 pc 40096438 /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
E/libc ( 7233): +++ ALLOCATION 0x404b9198 SIZE 10 FREED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c7d2 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d94 /system/lib/libc.so
E/libc ( 7233): #03 pc 40096462 /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
E/libc ( 7233): +++ ALLOCATION 0x404b9358 SIZE 10 HAS A CORRUPTED FRONT GUARD
E/libc ( 7233): +++ ALLOCATION 0x404b9358 SIZE 10 ALLOCATED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c658 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d80 /system/lib/libc.so
E/libc ( 7233): #03 pc 400964ba /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
E/libc ( 7233): +++ ALLOCATION 0x404b9358 SIZE 10 FREED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c7d2 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d94 /system/lib/libc.so
E/libc ( 7233): #03 pc 400964e4 /system/bin/malloctest
E/libc ( 7233): #04 pc 00016f24 /system/lib/libc.so
The following for a memory leak:
E/libc ( 7233): +++ THERE ARE 1 LEAKED ALLOCATIONS
E/libc ( 7233): +++ DELETING 4096 BYTES OF LEAKED MEMORY AT 0x404b95e8 (1 REMAINING)
E/libc ( 7233): +++ ALLOCATION 0x404b95e8 SIZE 4096 ALLOCATED HERE:
E/libc ( 7233): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
E/libc ( 7233): #00 pc 0000c35a /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #01 pc 0000c658 /system/lib/libc_malloc_debug_leak.so
E/libc ( 7233): #02 pc 00016d80 /system/lib/libc.so
E/libc ( 7233): #03 pc 0001bc94 /system/lib/libc.so
E/libc ( 7233): #04 pc 0001edf6 /system/lib/libc.so
E/libc ( 7233): #05 pc 0001b80a /system/lib/libc.so
E/libc ( 7233): #06 pc 0001c086 /system/lib/libc.so
E/libc ( 7233): #07 pc 40096402 /system/bin/malloctest
E/libc ( 7233): #08 pc 00016f24 /system/lib/libc.so
Change-Id: Ic440e9d05a01e2ea86b25e8998714e88bc2d16e0
Signed-off-by: Iliyan Malchev <malchev@google.com>
This change is intended to eliminate need to replace libc.so with libc_debug.so in order to enablememory allocation debugging.
This is also the first step towards implementing extended memoryallocation debugging using emulator's capabilities in monitoring memory access.
Iliyan Malchev
Vladimir Chtchetkine