From: Simon Glass <simon.glass@canonical.com> Document the practical workflow for detecting and diagnosing memory leaks in U-Boot, particularly in sandbox builds. This covers: - Using ut_check_delta() in unit tests for leak detection - Comparing heap dumps with malloc_dump_to_file() - Using malloc traffic logging to trace allocations - Verifying debug functions don't affect heap state - A step-by-step practical workflow Co-developed-by: Claude <noreply@anthropic.com> Signed-off-by: Simon Glass <simon.glass@canonical.com> --- doc/develop/malloc.rst | 93 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 93 insertions(+) diff --git a/doc/develop/malloc.rst b/doc/develop/malloc.rst index 776294809b8..9becd573e8c 100644 --- a/doc/develop/malloc.rst +++ b/doc/develop/malloc.rst @@ -418,6 +418,99 @@ malloc testing Unit tests can use malloc_enable_testing() to simulate allocation failures. +Finding Memory Leaks +~~~~~~~~~~~~~~~~~~~~ + +U-Boot provides several tools for detecting and diagnosing memory leaks. +These techniques are primarily supported on sandbox, which has the full +debugging infrastructure enabled by default (``CONFIG_MALLOC_DEBUG``, +``CONFIG_MCHECK_HEAP_PROTECTION``) and access to host filesystem functions +for writing dump files. + +**Leak detection in unit tests** + +Unit tests can use ``ut_check_delta()`` to detect memory leaks:: + + ulong mem_start; + + mem_start = ut_check_delta(0); /* Record starting heap usage */ + + /* ... test code that allocates and frees memory ... */ + + ut_asserteq(0, ut_check_delta(mem_start)); /* Verify no leak */ + +This uses ``mallinfo().uordblks`` to compare heap usage before and after. + +**Heap dump comparison** + +When a leak is detected, use ``malloc_dump()`` to capture heap state before +and after the operation. In sandbox builds, ``malloc_dump_to_file()`` writes +the dump to a host file for easier comparison:: + + malloc_dump_to_file("/tmp/before.txt"); + + /* ... operation that may leak ... */ + + malloc_dump_to_file("/tmp/after.txt"); + +Then compare the dumps to find leaked allocations:: + + $ diff /tmp/before.txt /tmp/after.txt + +Or extract just the addresses and sizes for comparison:: + + $ awk '{print $1, $2}' /tmp/before.txt | sort > /tmp/b.txt + $ awk '{print $1, $2}' /tmp/after.txt | sort > /tmp/a.txt + $ comm -13 /tmp/b.txt /tmp/a.txt # Show allocations only in 'after' + +The dump includes caller information when ``CONFIG_MCHECK_HEAP_PROTECTION`` +is enabled, showing exactly where each leaked allocation originated. + +**Malloc-traffic logging** + +For more detailed analysis, use the malloc-traffic log to record all +allocations during an operation:: + + malloc_log_start(); + + /* ... operation to trace ... */ + + malloc_log_stop(); + malloc_log_to_file("/tmp/malloc_log.txt"); /* Sandbox only */ + +The log shows every malloc(), free(), and realloc() call with addresses, sizes, +and caller backtraces (if enabled). Search for allocations that were never +freed:: + + $ grep "alloc" /tmp/malloc_log.txt # Find all allocations + $ grep "16ad1290" /tmp/malloc_log.txt # Check if a specific address was freed + +**Verifying debug functions don't allocate** + +When using these debugging functions, verify they don't affect heap state +by checking ``malloc_get_info()`` before and after:: + + struct malloc_info before, after; + + malloc_get_info(&before); + malloc_dump_to_file("/tmp/dump.txt"); + malloc_get_info(&after); + + /* Verify no allocations occurred */ + assert(before.malloc_count == after.malloc_count); + assert(before.in_use_bytes == after.in_use_bytes); + +**Practical workflow** + +1. Add ``ut_check_delta()`` assertions to your test to detect leaks +2. When a leak is detected, add ``malloc_dump_to_file()`` calls before and + after the leaking operation +3. Run the test and compare the dump files to identify leaked allocations +4. Use the caller backtrace in the dump to find the allocation site +5. If more detail is needed, enable ``malloc_log_start()`` to trace all + allocations during the operation +6. Fix the leak and verify the test passes + API Reference ------------- -- 2.43.0