ESP-IDF Heap Trace Issue Malloc Memory Allocation Not Traced

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Introduction

This article addresses an issue encountered in ESP-IDF version v5.4.1 where the heap trace component fails to track memory allocated using the standard malloc function. The expected behavior is for the heap trace to monitor all heap memory allocations, including those made with malloc, but the actual behavior only traces memory allocated via heap_caps_malloc. This discrepancy can hinder effective memory leak detection and debugging. This article provides an in-depth exploration of the issue, including steps to reproduce it, debug logs, and potential solutions.

Problem Description

The core issue is that the heap trace functionality in ESP-IDF v5.4.1 does not accurately monitor memory allocations made using the standard C library function malloc. Instead, it primarily tracks allocations performed with the ESP-IDF specific heap_caps_malloc. This limitation can lead to incomplete heap usage analysis and make it difficult to identify memory leaks originating from malloc calls. Understanding the nuances of memory management in embedded systems is crucial for developing robust and reliable applications. Efficient memory utilization is not just about preventing crashes; it's also about optimizing performance and ensuring long-term system stability. When memory leaks occur, they gradually consume available memory, leading to slowdowns and eventually system failure. Therefore, having a reliable heap tracing mechanism is vital for debugging and maintaining embedded software.

Expected Behavior

The heap trace component should trace all heap memory allocations, regardless of whether they are made using malloc or heap_caps_malloc. This comprehensive tracing is crucial for accurate memory usage analysis and leak detection. A robust heap tracing tool should provide a detailed snapshot of all memory allocations, allowing developers to pinpoint the exact locations in their code where memory is being allocated and, more importantly, where it might be leaked. This level of granularity is essential for identifying and fixing memory management issues, especially in complex embedded systems where memory resources are often limited.

Actual Behavior

The heap trace dump only shows memory allocated by heap_caps_malloc, effectively ignoring allocations made with the standard malloc. This incomplete tracing hinders the ability to detect memory leaks originating from standard library calls. This behavior can be particularly problematic in projects that heavily rely on malloc for dynamic memory allocation. The inability to trace these allocations means that developers are essentially flying blind when it comes to memory management, making it difficult to identify and resolve memory-related issues. This limitation underscores the need for a more comprehensive heap tracing solution that captures all memory allocation activities.

Steps to Reproduce

To reproduce this issue, the following code snippet can be used within an ESP-IDF project:

#include <unity.h>
#include <esp_heap_caps.h>
#include <esp_heap_trace.h>

static void testHeapTracer() {
    static heap_trace_record_t record[100];
    heap_trace_init_standalone(record,100);
    heap_trace_start(HEAP_TRACE_LEAKS);
    printf("%d\n",heap_caps_get_free_size(MALLOC_CAP_INTERNAL));

    void* ptr1 = malloc(128);
    void* ptr2 = heap_caps_malloc(256, MALLOC_CAP_DEFAULT);
    auto leaked = malloc(150);
    leaked = malloc(100);
    free(ptr1);
    heap_caps_free(ptr2);

    printf("%d\n",heap_caps_get_free_size(MALLOC_CAP_INTERNAL));

    heap_trace_stop();
    heap_trace_dump();
}

extern "C" void app_main() {
    UNITY_BEGIN();

    RUN_TEST(testHeapTracer);

    UNITY_END();
}

This code snippet initializes the heap trace, allocates memory using both malloc and heap_caps_malloc, and then frees some of the allocated memory. The heap_trace_dump() function is then called to display the heap trace results. The expected output should show all allocations, but the actual output only includes allocations made with heap_caps_malloc. This discrepancy clearly demonstrates the issue.

Detailed Breakdown of the Code

  1. Include Headers:
    • unity.h: For unit testing framework.
    • esp_heap_caps.h: For heap capabilities and allocation functions.
    • esp_heap_trace.h: For heap tracing functionality.
  2. testHeapTracer Function:
    • static heap_trace_record_t record[100];: Declares a static array to store heap trace records.
    • heap_trace_init_standalone(record,100);: Initializes the heap trace with the provided record array and size.
    • heap_trace_start(HEAP_TRACE_LEAKS);: Starts heap tracing in leak detection mode.
    • printf("%d\n",heap_caps_get_free_size(MALLOC_CAP_INTERNAL));: Prints the free size of internal heap memory.
    • void* ptr1 = malloc(128);: Allocates 128 bytes of memory using malloc.
    • void* ptr2 = heap_caps_malloc(256, MALLOC_CAP_DEFAULT);: Allocates 256 bytes of memory using heap_caps_malloc with default capabilities.
    • auto leaked = malloc(150); leaked = malloc(100);: Allocates 150 bytes and then 100 bytes using malloc without freeing, simulating a memory leak.
    • free(ptr1);: Frees the memory allocated by malloc.
    • heap_caps_free(ptr2);: Frees the memory allocated by heap_caps_malloc.
    • printf("%d\n",heap_caps_get_free_size(MALLOC_CAP_INTERNAL));: Prints the free size of internal heap memory after allocations and deallocations.
    • heap_trace_stop();: Stops heap tracing.
    • heap_trace_dump();: Dumps the heap trace records to the console.
  3. app_main Function:
    • UNITY_BEGIN();: Initializes the Unity testing framework.
    • RUN_TEST(testHeapTracer);: Runs the testHeapTracer function as a test case.
    • UNITY_END();: Finalizes the Unity testing framework.

Key Observations

  • The code allocates memory using both malloc and heap_caps_malloc to demonstrate the tracing discrepancy.
  • Memory is deliberately leaked using malloc to test the leak detection capabilities of the heap tracer.
  • The heap_trace_dump() function is crucial for observing which allocations are being tracked.

Debug Logs

The following debug logs illustrate the issue:

ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0x8 (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fce2810,len:0x15a0
load:0x403c8700,len:0x4
load:0x403c8704,len:0xd20
load:0x403cb700,len:0x2f00
entry 0x403c8920
I (27) boot: ESP-IDF 5.4.1 2nd stage bootloader
I (27) boot: compile time Jul 22 2025 12:29:41
I (27) boot: Multicore bootloader
I (27) boot: chip revision: v0.2
I (30) boot: efuse block revision: v1.3
I (33) boot.esp32s3: Boot SPI Speed : 80MHz
I (37) boot.esp32s3: SPI Mode       : DIO
I (41) boot.esp32s3: SPI Flash Size : 8MB
I (45) boot: Enabling RNG early entropy source...
I (49) boot: Partition Table:
I (52) boot: ## Label            Usage          Type ST Offset   Length
I (58) boot:  0 nvs              WiFi data        01 02 00009000 00005000
I (65) boot:  1 otadata          OTA data         01 00 0000e000 00002000
I (71) boot:  2 app0             OTA app          00 10 00010000 002e0000
I (78) boot:  3 littlefs         Unknown data     01 83 002f0000 00400000
I (84) boot:  4 coredump         Unknown data     01 03 006f0000 00010000
I (91) boot: End of partition table
I (94) esp_image: segment 0: paddr=00010020 vaddr=3c030020 size=0d898h ( 55448) map
I (111) esp_image: segment 1: paddr=0001d8c0 vaddr=3fc93d00 size=02758h ( 10072) load
I (114) esp_image: segment 2: paddr=00020020 vaddr=42000020 size=2a6d4h (173780) map
I (147) esp_image: segment 3: paddr=0004a6fc vaddr=3fc96458 size=00668h (  1640) load
I (148) esp_image: segment 4: paddr=0004ad6c vaddr=40374000 size=0fc48h ( 64584) load
I (165) esp_image: segment 5: paddr=0005a9bc vaddr=600fe100 size=0001ch (    28) load
I (171) boot: Loaded app from partition at offset 0x10000
I (171) boot: Disabling RNG early entropy source...
I (183) esp_psram: Found 2MB PSRAM device
I (183) esp_psram: Speed: 40MHz
I (183) cpu_start: Multicore app
I (602) esp_psram: SPI SRAM memory test OK
I (611) cpu_start: Pro cpu start user code
I (611) cpu_start: cpu freq: 160000000 Hz
I (611) app_init: Application information:
I (611) app_init: Project name:     Pixu
I (615) app_init: App version:      d05c181-dirty
I (619) app_init: Compile time:     Jul 22 2025 12:29:23
I (624) app_init: ELF file SHA256:  ff9a741da...
I (629) app_init: ESP-IDF:          5.4.1
I (632) efuse_init: Min chip rev:     v0.0
I (636) efuse_init: Max chip rev:     v0.99 
I (640) efuse_init: Chip rev:         v0.2
I (644) heap_init: Initializing. RAM available for dynamic allocation:
I (650) heap_init: At 3FC98490 len 00051280 (324 KiB): RAM
I (655) heap_init: At 3FCE9710 len 00005724 (21 KiB): RAM
I (660) heap_init: At 3FCF0000 len 00008000 (32 KiB): DRAM
I (666) heap_init: At 600FE11C len 00001ECC (7 KiB): RTCRAM
I (671) esp_psram: Adding pool of 2048K of PSRAM memory to heap allocator
I (679) spi_flash: detected chip: boya
I (681) spi_flash: flash io: dio
I (684) sleep_gpio: Configure to isolate all GPIO pins in sleep state
I (690) sleep_gpio: Enable automatic switching of GPIO sleep configuration
I (697) coexist: coex firmware version: e727207
I (721) coexist: coexist rom version e7ae62f
I (722) main_task: Started on CPU0
I (723) esp_psram: Reserving pool of 32K of internal memory for DMA/internal allocations
I (725) main_task: Calling app_main()
371035
371035
====== Heap Trace: 0 records (100 capacity) ======
====== Heap Trace Summary ======
Mode: Heap Trace Leaks
0 bytes 'leaked' in trace (0 allocations)
records: 0 (100 capacity, 1 high water mark)
total allocations: 1
total frees: 1
================================
test/test_pixu.cpp:339:testHeapTracer:PASS

The key observation from these logs is the "Heap Trace Summary" section. It indicates that 0 bytes are leaked and only a single allocation and free operation are recorded. This confirms that only the heap_caps_malloc allocation is being traced, while the malloc allocations are ignored. This discrepancy highlights a significant limitation in the heap tracing functionality, as it fails to capture a complete picture of memory usage within the application. The consequences of this incomplete tracing can be severe, as memory leaks originating from standard malloc calls may go undetected, leading to application instability and crashes over time. Therefore, addressing this issue is crucial for ensuring the reliability and robustness of ESP-IDF applications.

Analysis of the Debug Logs

  1. Boot Process: The logs show the standard ESP32-S3 boot process, including the bootloader version, chip revision, and flash configuration. These initial logs are important for verifying that the device is starting up correctly and that the flash memory is properly initialized.
  2. Memory Initialization: The heap initialization logs indicate the available RAM regions for dynamic allocation. This information is crucial for understanding the memory layout and ensuring that the application has sufficient memory resources. The logs show the available memory regions, including RAM and DRAM, along with their respective sizes. These details are essential for optimizing memory usage and preventing memory-related issues.
  3. PSRAM Initialization: The logs confirm the presence and initialization of 2MB of PSRAM. PSRAM (Pseudo-Static RAM) provides additional memory space for the application, which is particularly useful for memory-intensive tasks. The logs show the speed of the PSRAM and the successful completion of the memory test, indicating that the PSRAM is functioning correctly.
  4. Heap Trace Summary: This is the most critical section for this issue. The summary shows that the heap trace recorded 0 bytes leaked and only one allocation and one free operation. This clearly demonstrates that the heap trace is not capturing the allocations made with the standard malloc function, as the test code allocates memory using both malloc and heap_caps_malloc. The discrepancy in the recorded allocations highlights the core issue: the heap trace mechanism is not comprehensively monitoring all memory allocations within the application.
  5. Test Result: The final line test/test_pixu.cpp:339:testHeapTracer:PASS indicates that the unit test passed. However, this does not mean that the heap tracing is working correctly; it simply means that the test case executed without any runtime errors. The underlying issue of incomplete heap tracing remains unresolved.

Potential Causes

The most likely cause is that the heap trace component is specifically designed to track only heap_caps_malloc allocations and does not hook into the standard malloc implementation. This could be due to architectural decisions or limitations in the current implementation. Understanding the potential causes is crucial for devising effective solutions. Several factors might contribute to this behavior, including:

  1. Design Scope: The heap trace component might have been initially designed to focus solely on ESP-IDF's heap management functions (heap_caps_malloc) and not the standard C library's malloc. This could be a deliberate design choice based on the intended use cases or the complexity of hooking into the standard malloc implementation.
  2. Implementation Complexity: Hooking into the standard malloc implementation can be challenging due to its internal workings and platform-specific variations. The heap trace component might not have the necessary hooks or mechanisms to intercept and track allocations made by malloc across different platforms and configurations.
  3. Performance Considerations: Tracing every malloc allocation could introduce significant overhead, potentially impacting the performance of the application. The heap trace component might prioritize performance by focusing on a subset of allocation functions, such as heap_caps_malloc, which are more directly under ESP-IDF's control.
  4. Integration Challenges: Integrating with the standard C library's memory management functions might pose compatibility issues or conflicts with other system components. The heap trace component might avoid these challenges by limiting its scope to ESP-IDF's heap management functions.

Possible Solutions

  1. Extend Heap Trace Component: Modify the heap trace component to hook into the standard malloc and free functions, providing comprehensive memory allocation tracking. This would involve significant code changes but would provide the most complete solution. Extending the heap trace component to include standard malloc and free functions would require significant modifications to the existing implementation. This could involve:
    • Interception Mechanisms: Implementing hooks or interception mechanisms to capture calls to malloc and free.
    • Data Structures: Updating the internal data structures to store information about allocations made via malloc.
    • Tracing Logic: Modifying the tracing logic to handle allocations and deallocations from both heap_caps_malloc and malloc.
  2. Implement a Wrapper: Create a wrapper around malloc and free that calls the original functions and also records the allocations in a separate data structure. This approach would add overhead but could be a simpler workaround. Creating a wrapper around malloc and free is a viable workaround that involves creating custom functions that call the original malloc and free functions while also recording the allocations in a separate data structure. This approach adds some overhead but can be a simpler way to track memory allocations made via the standard C library functions. The wrapper functions would need to:
    • Allocate Memory: Call the original malloc to allocate the requested memory.
    • Record Allocation: Store information about the allocation, such as the address, size, and allocation time, in a separate data structure (e.g., a linked list or array).
    • Free Memory: Call the original free to deallocate the memory.
    • Remove Record: Remove the allocation record from the data structure.
  3. Use Memory Debugging Tools: Employ external memory debugging tools that can track all memory allocations, regardless of the allocation function used. This could involve integrating with tools like Valgrind or custom memory analysis scripts. Employing external memory debugging tools is another effective solution for tracking all memory allocations, regardless of the allocation function used. These tools can provide comprehensive memory usage analysis and help identify memory leaks and other memory-related issues. Some popular memory debugging tools include:
    • Valgrind: A powerful memory debugging and profiling tool for Linux-based systems.
    • AddressSanitizer (ASan): A memory error detector that can be integrated into the build process.
    • Custom Memory Analysis Scripts: Scripts that analyze memory dumps or logs to identify memory leaks and other issues.

Conclusion

The heap trace component in ESP-IDF v5.4.1 failing to trace memory allocated by malloc presents a significant challenge for memory debugging. Understanding the issue, reproducing it, and exploring potential solutions are crucial steps in addressing this limitation. While extending the heap trace component or implementing a wrapper around malloc and free are viable options, utilizing external memory debugging tools may offer a more comprehensive solution. By addressing this issue, developers can ensure more robust and reliable ESP-IDF applications. Robust memory management is a cornerstone of reliable embedded systems development. The ability to accurately track and analyze memory usage is essential for preventing memory leaks, optimizing performance, and ensuring the long-term stability of embedded applications. The limitations in the heap tracing functionality, as highlighted in this article, underscore the importance of continuous improvement and refinement of debugging tools and techniques. By addressing these limitations, developers can gain better visibility into their application's memory behavior and build more resilient systems.

FAQ

Why is heap tracing important in embedded systems?

Heap tracing is crucial in embedded systems because memory resources are often limited, and memory leaks can lead to system instability and crashes. It helps developers monitor memory usage, identify leaks, and optimize memory allocation.

What is the difference between malloc and heap_caps_malloc?

malloc is the standard C library function for dynamic memory allocation, while heap_caps_malloc is an ESP-IDF specific function that allows allocating memory with specific capabilities, such as being in internal RAM or PSRAM.

Can I use external tools to trace memory allocated by malloc?

Yes, external memory debugging tools like Valgrind or AddressSanitizer (ASan) can be used to track all memory allocations, including those made by malloc.

What are the potential workarounds for this issue?

Potential workarounds include extending the heap trace component, implementing a wrapper around malloc and free, or using external memory debugging tools.

How can I contribute to fixing this issue in ESP-IDF?

You can contribute by reporting the issue on the ESP-IDF GitHub repository, providing detailed information and steps to reproduce, and potentially submitting a pull request with a proposed solution.