[asterisk-dev] [Code Review] 2567: Add backtrace generation to MALLOC_DEBUG

[Matt Jordan]

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https://reviewboard.asterisk.org/r/2567/
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Review request for Asterisk Developers and rmudgett.


Repository: Asterisk


Description
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Richard's patch that added a 'mini-valgrind' into Asterisk is incredibly useful. When you have a memory corruption, it will tell you the particular location in Asterisk that allocated the memory. Unfortunately, this often simply tells you the needle to look for in a stack of needles. For example, a memory corruption caused by improper JSON reference counting may just tell you this:

WARNING: Memory corrupted after free of 0x27eb8e0 allocated at json.c json_malloc() line 52

Since there's a whole mess of json_malloc calls, this is only so useful.

Luckily, we have backtrace generation in Asterisk - which is used primarily by DEBUG_THREADS and locations where Asterisk with DO_CRASH enabled will abort. This patch refactors the backtrace generation code into its own translation unit so that astmm.c can get at it safely, and adds an ast_bt object to the region memory structure. When a memory region is allocated or used, a backtrace is generated so that if the memory becomes corrupted, we know who originally allocated it.

That turns the previous line into this:

WARNING: Memory corrupted after free of 0x27eb8e0 allocated at json.c json_malloc() line 52
Memory allocation backtrace:
#0: [0x4593e5] main/astmm.c:498 __ast_malloc() (0x4593a9+3C)
#1: [0x532f3a] main/json.c:53 json_malloc()
#2: [0x7f9e93c3a8ca] src/value.c:40 json_object() (0x7f9e93c3a8b0+1A)
#3: [0x7f9e93c396dd] src/pack_unpack.c:91 pack_object()
#4: [0x7f9e93c39be0] src/pack_unpack.c:550 json_vpack_ex() (0x7f9e93c39b50+90)
#5: [0x533ce6] main/json.c:496 ast_json_vpack() (0x533caa+3C)
#6: [0x533c9a] main/json.c:488 ast_json_pack() (0x533bfb+9F)
#7: [0x44e580] main/asterisk.c:1168 publish_fully_booted()
#8: [0x4583bd] main/asterisk.c:4444 main()


Diffs
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  /trunk/include/asterisk/backtrace.h PRE-CREATION 
  /trunk/include/asterisk/lock.h 389768 
  /trunk/include/asterisk/logger.h 389768 
  /trunk/main/astmm.c 389768 
  /trunk/main/astobj2.c 389768 
  /trunk/main/backtrace.c PRE-CREATION 
  /trunk/main/logger.c 389768 
  /trunk/utils/extconf.c 389768 

Diff: https://reviewboard.asterisk.org/r/2567/diff/


Testing
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Fixed two memory corruptions thanks to this patch. Yay MALLOC_DEBUG.


Thanks,

Matt Jordan

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