Heap Memory Debugging

[中文]

Overview

ESP-IDF integrates tools for requesting heap information, heap corruption detection, and heap tracing. These can help track down memory-related bugs.

For general information about the heap memory allocator, see Heap Memory Allocation.

Heap Information

To obtain information about the state of the heap, call the following functions:

Heap Allocation and Free Function Hooks

Users can use allocation and free detection hooks to be notified of every successful allocation and free operation:

  • Providing a definition of esp_heap_trace_alloc_hook() allows you to be notified of every successful memory allocation operation

  • Providing a definition of esp_heap_trace_free_hook() allows you to be notified of every successful memory-free operations

This feature can be enabled by setting the CONFIG_HEAP_USE_HOOKS option. esp_heap_trace_alloc_hook() and esp_heap_trace_free_hook() have weak declarations (e.g., __attribute__((weak))), thus it is not necessary to provide declarations for both hooks. Given that it is technically possible to allocate and free memory from an ISR (though strongly discouraged from doing so), the esp_heap_trace_alloc_hook() and esp_heap_trace_free_hook() can potentially be called from an ISR.

It is not recommended to perform (or call API functions to perform) blocking operations or memory allocation/free operations in the hook functions. In general, the best practice is to keep the implementation concise and leave the heavy computation outside of the hook functions.

The example below shows how to define the allocation and free function hooks:

#include "esp_heap_caps.h"

void esp_heap_trace_alloc_hook(void* ptr, size_t size, uint32_t caps)
{
  ...
}
void esp_heap_trace_free_hook(void* ptr)
{
  ...
}

void app_main()
{
  ...
}

Memory Allocation Failed Hook

Users can use heap_caps_register_failed_alloc_callback() to register a callback that is invoked every time an allocation operation fails.

Additionally, users can enable the CONFIG_HEAP_ABORT_WHEN_ALLOCATION_FAILS, which will automatically trigger a system abort if any allocation operation fails.

The example below shows how to register an allocation failure callback:

#include "esp_heap_caps.h"

void heap_caps_alloc_failed_hook(size_t requested_size, uint32_t caps, const char *function_name)
{
  printf("%s was called but failed to allocate %d bytes with 0x%X capabilities. \n",function_name, requested_size, caps);
}

void app_main()
{
    ...
    esp_err_t error = heap_caps_register_failed_alloc_callback(heap_caps_alloc_failed_hook);
    ...
    void *ptr = heap_caps_malloc(allocation_size, MALLOC_CAP_DEFAULT);
    ...
}

Heap Corruption Detection

Heap corruption detection allows you to detect various types of heap memory errors:

  • Out-of-bound writes & buffer overflows

  • Writes to freed memory

  • Reads from freed or uninitialized memory

Three levels of corruption detection are available. Each one providing a finer level of detection than the previous:

Assertions

The heap implementation (heap/multi_heap.c, etc.) includes numerous assertions that will fail if the heap memory is corrupted. To detect heap corruption most effectively, ensure that assertions are enabled in the project configuration via the CONFIG_COMPILER_OPTIMIZATION_ASSERTION_LEVEL option.

If a heap integrity assertion fails, a line will be printed like CORRUPT HEAP: multi_heap.c:225 detected at 0x3ffbb71c. The memory address printed is the address of the heap structure that has corrupt content.

It is also possible to manually check heap integrity by calling heap_caps_check_integrity_all() or related functions. This function checks all of the requested heap memory for integrity and can be used even if assertions are disabled. If the integrity checks detects an error, it will print the error along with the address(es) of corrupt heap structures.

Finding Heap Corruption

Memory corruption can be one of the hardest classes of bugs to find and fix, as the source of the corruption could be completely unrelated to the symptoms of the corruption. Here are some tips:

  • A crash with a CORRUPT HEAP: message usually includes a stack trace, but this stack trace is rarely useful. The crash is the symptom of memory corruption when the system realizes the heap is corrupt. But usually, the corruption happens elsewhere and earlier in time.

  • Increasing the heap memory debugging Configuration level to "Light impact" or "Comprehensive" gives you a more accurate message with the first corrupt memory address.

  • Adding regular calls to heap_caps_check_integrity_all() or heap_caps_check_integrity_addr() in your code helps you pin down the exact time that the corruption happened. You can move these checks around to "close in on" the section of code that corrupted the heap.

  • Based on the memory address that has been corrupted, you can use JTAG debugging to set a watchpoint on this address and have the CPU halt when it is written to.

  • If you do not have JTAG, but you do know roughly when the corruption happens, set a watchpoint in software just beforehand via esp_cpu_set_watchpoint(). A fatal exception will occur when the watchpoint triggers. The following is an example of how to use the function - esp_cpu_set_watchpoint(0, (void *)addr, 4, ESP_WATCHPOINT_STORE). Note that watchpoints are per-CPU and are set on the current running CPU only. So if you do not know which CPU is corrupting memory, call this function on both CPUs.

  • For buffer overflows, heap tracing in HEAP_TRACE_ALL mode tells which callers are allocating which addresses from the heap. See Heap Tracing To Find Heap Corruption for more details. You can try to find the function that allocates memory with an address immediately before the corrupted address, since it is probably the function that overflows the buffer.

  • Calling heap_caps_dump() or heap_caps_dump_all() can give an indication of what heap blocks are surrounding the corrupted region and may have overflowed or underflowed, etc.

Configuration

Temporarily increasing the heap corruption detection level can give more detailed information about heap corruption errors.

In the project configuration menu, under Component config, there is a menu Heap memory debugging. The option CONFIG_HEAP_CORRUPTION_DETECTION can be set to one of the following three levels:

Basic (No Poisoning)

This is the default level. By default, no special heap corruption features are enabled, but the provided assertions are enabled. A heap corruption error will be printed if any of the heap's internal data structures appear overwritten or corrupted. This usually indicates a buffer overrun or out-of-bounds write.

If assertions are enabled, an assertion will also trigger if a double-free occurs (the same memory is freed twice).

Calling heap_caps_check_integrity() in Basic mode checks the integrity of all heap structures, and print errors if any appear to be corrupted.

Light Impact

This level incorporates the "Basic" detection features. Additionally, each block of memory allocated is "poisoned" with head and tail "canary bytes". If an application writes over the "canary bytes", they will be seen as corrupted and integrity checks will fail.

The head canary word is 0xABBA1234 (3412BAAB in byte order), and the tail canary word is 0xBAAD5678 (7856ADBA in byte order).

With basic heap corruption checks, most out-of-bound writes can be detected and the number of overrun bytes before a failure is detected depends on the properties of the heap. However, the Light Impact mode is more precise as even a single-byte overrun can be detected.

Enabling light-impact checking increases the memory usage since each individual allocation uses additional bytes of metadata.

Each time heap_caps_free() is called in Light Impact mode, the head and tail canary bytes of the buffer being freed are checked against the expected values.

When heap_caps_check_integrity() or heap_caps_check_integrity_all() is called, all allocated blocks of heap memory have their canary bytes checked against the expected values.

In both cases, the functions involve checking that the first 4 bytes of an allocated block (before the buffer is returned to the user) should be the word 0xABBA1234, and the last 4 bytes of the allocated block (after the buffer is returned to the user) should be the word 0xBAAD5678.

Different values usually indicate buffer underrun or overrun. Overrun indicates that when writing to memory, the data written exceeds the size of the allocated memory, resulting in writing to an unallocated memory area; underrun indicates that when reading memory, the data read exceeds the allocated memory and reads data from an unallocated memory area.

Comprehensive

This level incorporates the "Light Impact" detection features. Additionally, it checks for uninitialized-access and use-after-free bugs. In this mode, all freshly allocated memory is filled with the pattern 0xCE, and all freed memory is filled with the pattern 0xFE.

Enabling Comprehensive mode has a substantial impact on runtime performance, as all memory needs to be set to the allocation patterns each time a heap_caps_malloc() or heap_caps_free() completes, and the memory also needs to be checked each time. However, this mode allows easier detection of memory corruptions which are much more subtle to find otherwise. It is recommended to only enable this mode when debugging, not in production.

The checks for allocated and free patterns (0xCE and respectively 0xFE) are also done when calling heap_caps_check_integrity() or heap_caps_check_integrity_all().

Crashes in Comprehensive Mode

If an application crashes when reading or writing an address related to 0xCECECECE in Comprehensive mode, it indicates that it has read uninitialized memory. The application should be changed to either use heap_caps_calloc() (which zeroes memory), or initialize the memory before using it. The value 0xCECECECE may also be seen in stack-allocated automatic variables, because, in ESP-IDF, most task stacks are originally allocated from the heap, and in C, stack memory is uninitialized by default.

If an application crashes, and the exception register dump indicates that some addresses or values were 0xFEFEFEFE, this indicates that it is reading heap memory after it has been freed, i.e., a "use-after-free bug". The application should be changed to not access heap memory after it has been freed.

If a call to heap_caps_malloc() or heap_caps_realloc() causes a crash because it was expected to find the pattern 0xFEFEFEFE in free memory and a different pattern was found, it indicates that the app has a use-after-free bug where it is writing to memory that has already been freed.

Manual Heap Checks in Comprehensive Mode

Calls to heap_caps_check_integrity() or heap_caps_check_integrity_all() may print errors relating to 0xFEFEFEFE, 0xABBA1234, or 0xBAAD5678. In each case the checker is expected to find a given pattern, and will error out if not found:

  • For free heap blocks, the checker expects to find all bytes set to 0xFE. Any other values indicate a use-after-free bug where free memory has been incorrectly overwritten.

  • For allocated heap blocks, the behavior is the same as for the Light Impact mode. The canary bytes 0xABBA1234 and 0xBAAD5678 are checked at the head and tail of each allocated buffer, and any variation indicates a buffer overrun or underrun.

Heap Task Tracking

Heap Task Tracking can be used to get per-task info for heap memory allocation. The application has to specify the heap capabilities for which the heap allocation is to be tracked.

Example code is provided in system/heap_task_tracking.

Heap Tracing

Heap Tracing allows the tracing of code which allocates or frees memory. Two tracing modes are supported:

  • Standalone. In this mode, traced data are kept on-board, so the size of the gathered information is limited by the buffer assigned for that purpose, and the analysis is done by the on-board code. There are a couple of APIs available for accessing and dumping collected info.

  • Host-based. This mode does not have the limitation of the standalone mode, because traced data are sent to the host over JTAG connection using app_trace library. Later on, they can be analyzed using special tools.

Heap tracing can perform two functions:

  • Leak checking: find memory that is allocated and never freed.

  • Heap use analysis: show all functions that are allocating or freeing memory while the trace is running.

How to Diagnose Memory Leaks

If you suspect a memory leak, the first step is to figure out which part of the program is leaking memory. Use the heap_caps_get_free_size() or related functions in heap information to track memory use over the life of the application. Try to narrow the leak down to a single function or sequence of functions where free memory always decreases and never recovers.

Standalone Mode

Once you have identified the code which you think is leaking:

  • Enable the CONFIG_HEAP_TRACING_DEST option.

  • Call the function heap_trace_init_standalone() early in the program, to register a buffer that can be used to record the memory trace.

  • Call the function heap_trace_start() to begin recording all mallocs or frees in the system. Call this immediately before the piece of code which you suspect is leaking memory.

  • Call the function heap_trace_stop() to stop the trace once the suspect piece of code has finished executing. This state will stop the tracing of both allocations and frees.

  • Call the function heap_trace_alloc_pause() to pause the tracing of new allocations while continuing to trace the frees. Call this immediately after the piece of code which you suspect is leaking memory to prevent any new allocations to be recorded.

  • Call the function heap_trace_dump() to dump the results of the heap trace.

The following code snippet demonstrates how application code would typically initialize, start, and stop heap tracing:

#include "esp_heap_trace.h"

#define NUM_RECORDS 100
static heap_trace_record_t trace_record[NUM_RECORDS]; // This buffer must be in internal RAM

...

void app_main()
{
    ...
    ESP_ERROR_CHECK( heap_trace_init_standalone(trace_record, NUM_RECORDS) );
    ...
}

void some_function()
{
    ESP_ERROR_CHECK( heap_trace_start(HEAP_TRACE_LEAKS) );

    do_something_you_suspect_is_leaking();

    ESP_ERROR_CHECK( heap_trace_stop() );
    heap_trace_dump();
    ...
}

The output from the heap trace has a similar format to the following example:

====== Heap Trace: 8 records (8 capacity) ======
    3 bytes (@ 0x3fcb26f8, Internal) allocated CPU 0 ccount 0x1e7af728 freed
    6 bytes (@ 0x3fcb4ff0, Internal) allocated CPU 0 ccount 0x1e7afc38 freed
    9 bytes (@ 0x3fcb5000, Internal) allocated CPU 0 ccount 0x1e7b01d4 freed
    12 bytes (@ 0x3fcb5010, Internal) allocated CPU 0 ccount 0x1e7b0778 freed
    15 bytes (@ 0x3fcb5020, Internal) allocated CPU 0 ccount 0x1e7b0d18 freed
    18 bytes (@ 0x3fcb5034, Internal) allocated CPU 0 ccount 0x1e7b12b8 freed
    21 bytes (@ 0x3fcb504c, Internal) allocated CPU 0 ccount 0x1e7b1858 freed
    24 bytes (@ 0x3fcb5068, Internal) allocated CPU 0 ccount 0x1e7b1dfc freed
====== Heap Trace Summary ======
Mode: Heap Trace All
0 bytes alive in trace (0/8 allocations)
records: 8 (8 capacity, 8 high water mark)
total allocations: 8
total frees: 8
================================

Note

The above example output uses IDF Monitor to automatically decode PC addresses to their source files and line numbers.

(NB: Internal Buffer has overflowed, so trace data is incomplete.) will be logged if the list of records overflow. If you see this log, consider either shortening the tracing period or increasing the number of records in the trace buffer.

(NB: New entries were traced while dumping, so trace dump may have duplicate entries.) will be logged in the summary if new entries are traced while calling heap_trace_dump() or heap_trace_dump_caps().

In HEAP_TRACE_LEAKS or HEAP_TRACE_ALL mode, for each traced memory allocation that has not already been freed, a line is printed with:

  • XX bytes is the number of bytes allocated.

  • @ 0x... is the heap address returned from heap_caps_malloc() or heap_caps_calloc() .

  • Internal or PSRAM is the general location of the allocated memory.

  • CPU x is the CPU (0 or 1) running when the allocation was made.

  • ccount 0x... is the CCOUNT (CPU cycle count) register value the allocation was made. The value is different for CPU 0 vs CPU 1.

In HEAP_TRACE_LEAKS mode, when memory is freed, the associated record is dropped.

In HEAP_TRACE_ALL:

  • when memory is freed, the associated record is kept in the list and its field freed is set to true.

  • After the maximum number of records is reached, old records are dropped and replaced with new records.

Finally, the total number of the 'leaked' bytes (bytes allocated but not freed while the trace is running) is printed together with the total number of allocations it represents.

Using hashmap for increased performance

By default, the heap tracing uses a statically allocated doubly-linked list to store the trace records. This has the disadvantage of causing runtime performance issues as the list gets fuller since the more items are in the list, the more time consuming it is to find a given item. This problem makes the use of the doubly linked list particularly inefficient if the user wishes to store a very large amount of records (to the point where the feature is simply no longer usable as the time it takes to retrieve an item in the list prevents the user application from executing properly).

For this reason, the option to use a hashmap mechanism to store records is available by enabling Component config > Heap Memory Debugging > CONFIG_HEAP_TRACE_HASH_MAP in the project configuration menu, allowing users to track significant amounts of records without suffering from drastic performance loss.

Each hashmap entry is a singly linked list of records sharing the same hash ID.

Each record hash ID is calculated based on the pointer to the memory they track. The hash function used is based on the Fowler-Noll-Vo hash function modified to ensure an even spread of all records in the range [0 ; hashmap size[ where hashmap size can be defined by setting Component config > Heap Memory Debugging > CONFIG_HEAP_TRACE_HASH_MAP_SIZE in the project configuration menu.

Note

  • The option CONFIG_HEAP_TRACE_HASH_MAP_SIZE defines the number of entries in the hashmap. The total number of records that can be stored is still defined by the user when calling heap_trace_init_standalone(). If N is the maximum number of records and H the number of entries in the hashmap, Then each entry will contain at max N / H records.

  • The hashmap complements the doubly-linked list and does not replace it. This means that the hashmap usage can create a significant memory overhead.

  • The memory used to store the hashmap is dynamically allocated (in internal memory by default) but by setting Component config > Heap Memory Debugging > CONFIG_HEAP_TRACE_HASH_MAP_IN_EXT_RAM, the user can force the hashmap in external memory (this option is available under the condition that CONFIG_SPIRAM is enabled).

Host-Based Mode

Once you have identified the code which you think is leaking:

  • In the project configuration menu, navigate to Component config > Heap Memory Debugging > CONFIG_HEAP_TRACING_DEST and select Host-Based.

  • In the project configuration menu, navigate to Component config > Application Level Tracing > CONFIG_APPTRACE_DESTINATION1 and select Trace memory.

  • In the project configuration menu, navigate to Component config > Application Level Tracing > FreeRTOS SystemView Tracing and enable CONFIG_APPTRACE_SV_ENABLE.

  • Call the function heap_trace_init_tohost() early in the program, to initialize the JTAG heap tracing module.

  • Call the function heap_trace_start() to begin recording all memory allocation and free calls in the system. Call this immediately before the piece of code which you suspect is leaking memory.

    In host-based mode, the argument to this function is ignored, and the heap tracing module behaves like HEAP_TRACE_ALL is passed, i.e., all allocations and deallocations are sent to the host.

  • Call the function heap_trace_stop() to stop the trace once the suspect piece of code has finished executing.

The following code snippet demonstrates how application code would typically initialize, start, and stop host-based mode heap tracing:

#include "esp_heap_trace.h"

...

void app_main()
{
    ...
    ESP_ERROR_CHECK( heap_trace_init_tohost() );
    ...
}

void some_function()
{
    ESP_ERROR_CHECK( heap_trace_start(HEAP_TRACE_LEAKS) );

    do_something_you_suspect_is_leaking();

    ESP_ERROR_CHECK( heap_trace_stop() );
    ...
}

To gather and analyze heap trace, do the following on the host:

  1. Build the program and download it to the target as described in Step 5. First Steps on ESP-IDF.

  2. Run OpenOCD (see JTAG Debugging).

Note

In order to use this feature, you need OpenOCD version v0.10.0-esp32-20181105 or later.

  1. You can use GDB to start and/or stop tracing automatically. To do this you need to prepare a special gdbinit file:

target remote :3333

mon reset halt
maintenance flush register-cache

tb heap_trace_start
commands
mon esp sysview start file:///tmp/heap.svdat
c
end

tb heap_trace_stop
commands
mon esp sysview stop
end

c

Using this file GDB can connect to the target, reset it, and start tracing when the program hits breakpoint at heap_trace_start(). Tracing will be stopped when the program hits breakpoint at heap_trace_stop(). Traced data will be saved to /tmp/heap_log.svdat.

  1. Run GDB using riscv32-esp-elf-gdb -x gdbinit </path/to/program/elf>.

  2. Quit GDB when the program stops at heap_trace_stop(). Traced data are saved in /tmp/heap.svdat.

  3. Run processing script $IDF_PATH/tools/esp_app_trace/sysviewtrace_proc.py -p -b </path/to/program/elf> /tmp/heap_log.svdat.

The output from the heap trace has a similar format to the following example:

Parse trace from '/tmp/heap.svdat'...
Stop parsing trace. (Timeout 0.000000 sec while reading 1 bytes!)
Process events from '['/tmp/heap.svdat']'...
[0.002244575] HEAP: Allocated 1 bytes @ 0x3ffaffd8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.002258425] HEAP: Allocated 2 bytes @ 0x3ffaffe0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:48
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.002563725] HEAP: Freed bytes @ 0x3ffaffe0 from task "free" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:31 (discriminator 9)
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.002782950] HEAP: Freed bytes @ 0x3ffb40b8 from task "main" on core 0 by:
/home/user/projects/esp/esp-idf/components/freertos/tasks.c:4590
/home/user/projects/esp/esp-idf/components/freertos/tasks.c:4590

[0.002798700] HEAP: Freed bytes @ 0x3ffb50bc from task "main" on core 0 by:
/home/user/projects/esp/esp-idf/components/freertos/tasks.c:4590
/home/user/projects/esp/esp-idf/components/freertos/tasks.c:4590

[0.102436025] HEAP: Allocated 2 bytes @ 0x3ffaffe0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.102449800] HEAP: Allocated 4 bytes @ 0x3ffaffe8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:48
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.102666150] HEAP: Freed bytes @ 0x3ffaffe8 from task "free" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:31 (discriminator 9)
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.202436200] HEAP: Allocated 3 bytes @ 0x3ffaffe8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.202451725] HEAP: Allocated 6 bytes @ 0x3ffafff0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:48
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.202667075] HEAP: Freed bytes @ 0x3ffafff0 from task "free" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:31 (discriminator 9)
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.302436000] HEAP: Allocated 4 bytes @ 0x3ffafff0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.302451475] HEAP: Allocated 8 bytes @ 0x3ffb40b8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:48
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.302667500] HEAP: Freed bytes @ 0x3ffb40b8 from task "free" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:31 (discriminator 9)
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

Processing completed.

Processed 1019 events

=============== HEAP TRACE REPORT ===============

Processed 14 heap events.

[0.002244575] HEAP: Allocated 1 bytes @ 0x3ffaffd8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.102436025] HEAP: Allocated 2 bytes @ 0x3ffaffe0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.202436200] HEAP: Allocated 3 bytes @ 0x3ffaffe8 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

[0.302436000] HEAP: Allocated 4 bytes @ 0x3ffafff0 from task "alloc" on core 0 by:
/home/user/projects/esp/esp-idf/examples/system/sysview_tracing_heap_log/main/sysview_heap_log.c:47
/home/user/projects/esp/esp-idf/components/freertos/port.c:355 (discriminator 1)

Found 10 leaked bytes in 4 blocks.

Heap Tracing To Find Heap Corruption

Heap tracing can also be used to help track down heap corruption. When a region in the heap is corrupted, it may be from some other part of the program that allocated memory at a nearby address.

If you have an approximate idea of when the corruption occurred, enabling heap tracing in HEAP_TRACE_ALL mode allows you to record all the memory allocation functions used and the corresponding allocation addresses.

Using heap tracing in this way is very similar to memory leak detection as described above. For memories that are allocated and not freed, the output is the same. However, records will also be shown for memory that has been freed.

Performance Impact

Enabling heap tracing in menuconfig increases the code size of your program, and has a very small negative impact on the performance of heap allocation or free operations even when heap tracing is not running.

When heap tracing is running, heap allocation or free operations are substantially slower than when heap tracing is stopped. Increasing the depth of stack frames recorded for each allocation (see above) also increases this performance impact.

To mitigate the performance loss when the heap tracing is enabled and active, enable CONFIG_HEAP_TRACE_HASH_MAP. With this configuration enabled, a hash map mechanism will be used to handle the heap trace records, thus considerably decreasing the heap allocation or free execution time. The size of the hash map can be modified by setting the value of CONFIG_HEAP_TRACE_HASH_MAP_SIZE.

By default, the hash map is placed into internal RAM. It can also be placed into external RAM if CONFIG_HEAP_TRACE_HASH_MAP_IN_EXT_RAM is enabled. In order to enable this configuration, make sure to enable CONFIG_SPIRAM and CONFIG_SPIRAM_ALLOW_BSS_SEG_EXTERNAL_MEMORY.

False-Positive Memory Leaks

Not everything printed by heap_trace_dump() is necessarily a memory leak. The following cases may also be printed:

  • Any memory that is allocated after heap_trace_start() but freed after heap_trace_stop() appears in the leaked dump.

  • Allocations may be made by other tasks in the system. Depending on the timing of these tasks, it is quite possible that this memory is freed after heap_trace_stop() is called.

  • The first time a task uses stdio - e.g., when it calls heap_caps_printf() - a lock, i.e., RTOS mutex semaphore, is allocated by the libc. This allocation lasts until the task is deleted.

  • Certain uses of heap_caps_printf(), such as printing floating point numbers and allocating some memory from the heap on demand. These allocations last until the task is deleted.

  • The Bluetooth, Wi-Fi, and TCP/IP libraries allocate heap memory buffers to handle incoming or outgoing data. These memory buffers are usually short-lived, but some may be shown in the heap leak trace if the data has been received or transmitted by the lower levels of the network during the heap tracing.

  • TCP connections retain some memory even after they are closed due to the TIME_WAIT state. Once the TIME_WAIT period is completed, this memory will be freed.

One way to differentiate between "real" and "false positive" memory leaks is to call the suspect code multiple times while tracing is running, and look for patterns (multiple matching allocations) in the heap trace output.

Application Examples

  • system/heap_task_tracking demonstrates the use of the heap task tracking feature to track heap memory allocated on a per-task basis.

API Reference - Heap Tracing

Header File

Functions

esp_err_t heap_trace_init_standalone(heap_trace_record_t *record_buffer, size_t num_records)

Initialise heap tracing in standalone mode.

This function must be called before any other heap tracing functions.

To disable heap tracing and allow the buffer to be freed, stop tracing and then call heap_trace_init_standalone(NULL, 0);

Parameters

  • record_buffer -- Provide a buffer to use for heap trace data. Note: External RAM is allowed, but it prevents recording allocations made from ISR's.

  • num_records -- Size of the heap trace buffer, as number of record structures.

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE Heap tracing is currently in progress.

  • ESP_OK Heap tracing initialised successfully.

esp_err_t heap_trace_init_tohost(void)

Initialise heap tracing in host-based mode.

This function must be called before any other heap tracing functions.

Returns

  • ESP_ERR_INVALID_STATE Heap tracing is currently in progress.

  • ESP_OK Heap tracing initialised successfully.

esp_err_t heap_trace_start(heap_trace_mode_t mode)

Start heap tracing. All heap allocations & frees will be traced, until heap_trace_stop() is called.

Note

heap_trace_init_standalone() must be called to provide a valid buffer, before this function is called.

Note

Calling this function while heap tracing is running will reset the heap trace state and continue tracing.

Parameters

mode -- Mode for tracing.

  • HEAP_TRACE_ALL means all heap allocations and frees are traced.

  • HEAP_TRACE_LEAKS means only suspected memory leaks are traced. (When memory is freed, the record is removed from the trace buffer.)

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE A non-zero-length buffer has not been set via heap_trace_init_standalone().

  • ESP_OK Tracing is started.

esp_err_t heap_trace_stop(void)

Stop heap tracing.

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE Heap tracing was not in progress.

  • ESP_OK Heap tracing stopped.

esp_err_t heap_trace_alloc_pause(void)

Pause heap tracing of allocations.

Note

This function puts the heap tracing in the state where the new allocations will no longer be traced but the free will still be. This can be used to e.g., strategically monitor a set of allocations to make sure each of them will get freed without polluting the list of records with unwanted allocations.

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE Heap tracing was not in progress.

  • ESP_OK Heap tracing paused.

esp_err_t heap_trace_resume(void)

Resume heap tracing which was previously stopped.

Unlike heap_trace_start(), this function does not clear the buffer of any pre-existing trace records.

The heap trace mode is the same as when heap_trace_start() was last called (or HEAP_TRACE_ALL if heap_trace_start() was never called).

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE Heap tracing was already started.

  • ESP_OK Heap tracing resumed.

size_t heap_trace_get_count(void)

Return number of records in the heap trace buffer.

It is safe to call this function while heap tracing is running.

esp_err_t heap_trace_get(size_t index, heap_trace_record_t *record)

Return a raw record from the heap trace buffer.

Note

It is safe to call this function while heap tracing is running, however in HEAP_TRACE_LEAK mode record indexing may skip entries unless heap tracing is stopped first.

Parameters

  • index -- Index (zero-based) of the record to return.

  • record -- [out] Record where the heap trace record will be copied.

Returns

  • ESP_ERR_NOT_SUPPORTED Project was compiled without heap tracing enabled in menuconfig.

  • ESP_ERR_INVALID_STATE Heap tracing was not initialised.

  • ESP_ERR_INVALID_ARG Index is out of bounds for current heap trace record count.

  • ESP_OK Record returned successfully.

void heap_trace_dump(void)

Dump heap trace record data to stdout.

Note

It is safe to call this function while heap tracing is running, however in HEAP_TRACE_LEAK mode the dump may skip entries unless heap tracing is stopped first.

void heap_trace_dump_caps(const uint32_t caps)

Dump heap trace from the memory of the capabilities passed as parameter.

Parameters

caps -- Capability(ies) of the memory from which to dump the trace. Set MALLOC_CAP_INTERNAL to dump heap trace data from internal memory. Set MALLOC_CAP_SPIRAM to dump heap trace data from PSRAM. Set both to dump both heap trace data.

esp_err_t heap_trace_summary(heap_trace_summary_t *summary)

Get summary information about the result of a heap trace.

Note

It is safe to call this function while heap tracing is running.

Structures

struct heap_trace_record_t

Trace record data type. Stores information about an allocated region of memory.

Public Members

uint32_t ccount

CCOUNT of the CPU when the allocation was made. LSB (bit value 1) is the CPU number (0 or 1).

void *address

Address which was allocated. If NULL, then this record is empty.

size_t size

Size of the allocation.

bool freed

State of the allocation (false if not freed, true if freed)

void *alloced_by[CONFIG_HEAP_TRACING_STACK_DEPTH]

Call stack of the caller which allocated the memory.

void *freed_by[CONFIG_HEAP_TRACING_STACK_DEPTH]

Call stack of the caller which freed the memory (all zero if not freed.)

struct heap_trace_summary_t

Stores information about the result of a heap trace.

Public Members

heap_trace_mode_t mode

The heap trace mode we just completed / are running.

size_t total_allocations

The total number of allocations made during tracing.

size_t total_frees

The total number of frees made during tracing.

size_t count

The number of records in the internal buffer.

size_t capacity

The capacity of the internal buffer.

size_t high_water_mark

The maximum value that 'count' got to.

size_t has_overflowed

True if the internal buffer overflowed at some point.

Macros

CONFIG_HEAP_TRACING_STACK_DEPTH

Type Definitions

typedef struct heap_trace_record_t heap_trace_record_t

Trace record data type. Stores information about an allocated region of memory.

Enumerations

enum heap_trace_mode_t

Values:

enumerator HEAP_TRACE_ALL
enumerator HEAP_TRACE_LEAKS

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