[Ovmsdev] Heap corruption alerts & heap tracing

Mon Dec 29 19:11:51 HKT 2025

Checking the heap immediately on events will probably not catch bugs 
that involve late callbacks using already freed buffers, and some events 
also are signaled before the actual shutdown (release of all resources) 
has fully taken place.

To register the heap checker for a delayed execution, use this scheme:

> # create custom heap checking event handler:
> vfs echo "module check alert" /store/events/usr.check.heap/00-checkheap
>
> # register delayed heap checks:
> vfs echo "event raise -d5000 usr.check.heap" 
> /store/events/server.v2.stopped/90-checkheap
> vfs echo "event raise -d5000 usr.check.heap" 
> /store/events/server.v3.stopped/90-checkheap
> …

Note: just guessing with the 5 second delay here, may need more, 
depending on the event.

Maybe we should register the check to be done by default on some 
selected events. Although the heap check normally is done within 
milliseconds, I still hesitate doing that. The heap check needs to lock 
the system while walking through all allocated memory blocks, which may 
create issues for vehicles that rely on consistent timing for CAN or 
custom hardware communication.

Regards,
Michael

Am 29.12.25 um 11:42 schrieb Michael Balzer via OvmsDev:
> The heap check + one-off alert function is now exposed for inclusion 
> in component code and can be called as a shell command to enable 
> inclusion in event scripts et al:
>
>> #include "ovms_module.h"
>>
>> /**
>>  * module_check_heap_alert: check for and send one-off alert 
>> notification on heap corruption
>>  *
>>  *    To enable the check every 5 minutes, set config "module" 
>> "debug.heap" to "yes".
>>  *
>>  *    To add custom checks, call from your code, or register event 
>> scripts as needed.
>>  *    Example: perform heap integrity check when the server V2 gets 
>> stopped:
>>  *      vfs echo "module check alert" 
>> /store/events/server.v2.stopped/90-checkheap
>>  *
>>  * @param verbosity     -- optional: channel capacity (default 0)
>>  * @param OvmsWriter    -- optional: channel (default NULL)
>>  * @return heapok       -- false = heap corrupted/full
>>  */
>> extern bool module_check_heap_alert(int verbosity=0, OvmsWriter* 
>> writer=NULL);
>
> Regards,
> Michael
>
>
> Am 28.12.25 um 19:21 schrieb Michael Balzer via OvmsDev:
>> PS: when creating a debug build, you may also consider enabling the 
>> "comprehensive" corruption detection mode, as that will catch more cases.
>>
>> But be aware that has a substantial impact on performance, so a user 
>> will probably not tolerate this for regular daily use.
>>
>> Regards,
>> Michael
>>
>>
>> Am 28.12.25 um 18:26 schrieb Michael Balzer via OvmsDev:
>>> Everyone,
>>>
>>> from the crash reports 
>>> (https://ovms.dexters-web.de/firmware/developer/), most remaining 
>>> crashes seem to be caused by heap corruptions.
>>>
>>> Not all heap corruptions are easily detectable from the backtrace 
>>> analysis, and the component or action causing the corruption isn't 
>>> detectable at all that way. So I've added a debug option to enable a 
>>> regular heap integrity check ever 5 minutes, with the module sending 
>>> an alert notification when a corruption has been detected. Example:
>>>
>>>> Heap corruption detected; reboot advised ASAP!
>>>> Please forward including task records and system log:
>>>>
>>>> CORRUPT HEAP: Bad tail at 0x3f8e44f0 owner 0x3ffea9bc. Expected 
>>>> 0xbaad5678 got 0xbaad5600
>>>
>>> I also added a final heap integrity check to our crash handler, so 
>>> the crash debug records should now show exactly which crashes 
>>> occurred with a corrupted heap.
>>>
>>> In combination with the system log and the task log, that should 
>>> give us some more opportunities to narrow down the cause(s).
>>>
>>> I've also added task ownershop to the heap corruption report. Note, 
>>> this needs my latest additions to our esp-idf fork, so take care to 
>>> pull these before building.
>>>
>>> Be aware, task ownership of corrupted blocks doesn't necessarily 
>>> tell about the task doing the corruption. If the tail canary is 
>>> compromised, and no other block located before that block is 
>>> compromised, it *may* be that task doing the out of bounds write. 
>>> But it may also be a use after free of some previous owner. So take 
>>> task ownership with a grain of salt.
>>>
>>> The corruptions are most probably caused by some unclean shutdown of 
>>> a component or by an undetected race conditions within a shutdown 
>>> procedure. The heap seems to be stable on modules with standard 
>>> configurations and components not being started & shut down on a 
>>> regular base. The heap corruptions are especially present now with 
>>> Smart (SQ) vehicles -- as the Smart doesn't keep the 12V battery 
>>> charged from the main battery, most Smart users probably use the 
>>> power management to shut down Wifi and/or modem while parking.
>>>
>>> So our main focus should be on analysing what happens before the 
>>> corruption. Ask users reporting heap corruptions to provide their 
>>> system logs, and possibly also their task logs. To encourage 
>>> enabling these, I've added the config to the web UI 
>>> (Config→Notifications).
>>>
>>>
>>> Once you can reproduce (!) the corruption, heap tracing might 
>>> provide some more insight as to where exactly the corruption occurs.
>>>
>>> Heap tracing means recording all memory allocations and frees. This 
>>> adds a recording layer on top of the heap functions, so comes with 
>>> some cost, even when inactive. CPU overhead is low, but stack 
>>> overhead may be an issue, so I think we should not enable heap 
>>> tracing by default for now, but rather use a debug build 
>>> specifically in cases we think heap tracing might help.
>>>
>>> To enable heap tracing on some user device, I've reworked the 
>>> ESP-IDF heap tracing to enable remote execution and to also include 
>>> the task handles performing the allocations and deallocations.
>>>
>>> To enable heap tracing for a build:
>>>
>>>>   * Under|makemenuconfig|, navigate
>>>>     to|Componentsettings|->|HeapMemoryDebugging|and
>>>>     setCONFIG_HEAP_TRACING
>>>>     <https://docs.espressif.com/projects/esp-idf/en/v3.3/api-reference/kconfig.html#config-heap-tracing>.
>>>>
>>>
>>> There's also an option to set the number of stack backtrace frames. 
>>> Tracing with two frames is mostly useless in our (C++) context, as 
>>> it will normally only show some inner frames of the allocator. I've 
>>> tried raising that to 5, and got an immediate crash in the mdns 
>>> component. I assume raising the depth will need raising some stack 
>>> sizes. If you find a good compromise, please report.
>>>
>>> Heap tracing will work best in a reduced configuration. In normal 
>>> operation, my module fills a 500 records buffer within seconds. The 
>>> buffer is a FIFO, so will always contain the latest n allocations, 
>>> and the last entry in the dump is the newest one.
>>>
>>> Reduced example dump:
>>>
>>>> OVMS# mod trace dump
>>>> Heap tracing started/resumed at ccount 0x1c70b453 = logtime 19415
>>>> 1000 allocations trace (1000 entry buffer)
>>>> 258 bytes (@ 0x3fffb3a8) allocated CPU 1 task 0x3ffc92e8 ccount 
>>>> 0x89074e74 caller 0x4031d4f0:0x4031f553
>>>> freed task 0x3ffc92e8 by 0x4031d514:0x4031f595
>>>> 201 bytes (@ 0x3f8e92f4) allocated CPU 1 task 0x3fff2290 ccount 
>>>> 0x89218bbc caller 0x40131b12:0x4014633c
>>>> freed task 0x3fff2290 by 0x402c4634:0x402cb14d
>>>> 112 bytes (@ 0x3ffebc80) allocated CPU 1 task 0x3ffee918 ccount 
>>>> 0x8a25d47c caller 0x4029b455:0x4017a5dc
>>>> freed task 0x3ffee918 by 0x4029b744:0x4017a5dc
>>>> 112 bytes (@ 0x3ffebc80) allocated CPU 1 task 0x3ffee918 ccount 
>>>> 0x8db89c40 caller 0x4029b455:0x4017a5dc
>>>> freed task 0x3ffee918 by 0x4029b744:0x4017a5dc
>>>> 12 bytes (@ 0x3f85d0d4) allocated CPU 1 task 0x3ffdfcd0 ccount 
>>>> 0x8fccdfd8 caller 0x40131b12:0x4014633c
>>>> freed task 0x3ffdfcd0 by 0x402c4634:0x401e0a04
>>>> […]
>>>> 12 bytes (@ 0x3f85d0d4) allocated CPU 1 task 0x3ffdfcd0 ccount 
>>>> 0x3cf429f4 caller 0x40131b12:0x4014633c
>>>> freed task 0x3ffdfcd0 by 0x402c4634:0x401e0a04
>>>> 112 bytes (@ 0x3ffebc80) allocated CPU 1 task 0x3ffee918 ccount 
>>>> 0x3fe1a0bc caller 0x4029b455:0x4017a5dc
>>>> 229 bytes alive in trace (3/1000 allocations)
>>>> total allocations 1207 total frees 3356
>>>> (NB: Buffer has overflowed; so trace data is incomplete.)
>>>
>>> "ccount" is the ESP32 CCOUNT register (CPU cycles), so provides an 
>>> orientation on when the allocation occurred.
>>>
>>>
>>> Some more basics on heap debugging are also covered here: 
>>> https://docs.espressif.com/projects/esp-idf/en/v3.3/api-reference/system/heap_debug.html
>>>
>>> Regards,
>>> Michael
>>>
>>> -- 
>>> Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
>>> Fon 02330 9104094 * Handy 0176 20698926
>>>
>>> _______________________________________________
>>> OvmsDev mailing list
>>> OvmsDev at lists.openvehicles.com
>>> http://lists.openvehicles.com/mailman/listinfo/ovmsdev
>>
>> -- 
>> Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
>> Fon 02330 9104094 * Handy 0176 20698926
>>
>>
>> _______________________________________________
>> OvmsDev mailing list
>> OvmsDev at lists.openvehicles.com
>> http://lists.openvehicles.com/mailman/listinfo/ovmsdev
>
> -- 
> Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
> Fon 02330 9104094 * Handy 0176 20698926
>
>
> _______________________________________________
> OvmsDev mailing list
> OvmsDev at lists.openvehicles.com
> http://lists.openvehicles.com/mailman/listinfo/ovmsdev

-- 
Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
Fon 02330 9104094 * Handy 0176 20698926

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