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Accelerated Linux Core Dump Analysis

Identify Heap Leaks

Explore methods to identify and diagnose heap memory leaks in Linux applications by analyzing core dumps using the GDB debugger. Understand how to examine memory sections, compare pmap logs, and detect patterns indicating progressive memory consumption. This lesson guides you through hands-on debugging practices to pinpoint causes of heap leaks in a practical example.

We'll cover the following...

The application App9 was found to consume more and more memory. There were several core memory dumps that were saved at different times with corresponding pmap logs. In this exercise, we’ll try to identify the cause of this memory leak.

Application source code

For reference, here’s the code of this application:

C
// Build:
// gcc main.c -pthread -static -o App9
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
void procD()
{
}
typedef void (**PFUNC)();
void procC(int iter)
{
    for (int i = 0; i < iter; ++i)
    {
        char *p = malloc(256);
        strcpy(p, "allocated memory");
        *(PFUNC)(p + 32) = &procD;
    }
}
void procB()
{
    procC(250000);
    sleep(300);
    procC(250000);
    sleep(-1);
}
void procA()
{
    procC(5000);
    sleep(300);
    procB();
}
#define THREAD_DECLARE(num, func) \
    void bar_##num()               \
    {                              \
        func;                      \
    }                              \
                                   \
    void foo_##num()               \
    {                              \
        bar_##num();               \
    }                              \
                                   \
    void *thread_##num(void *arg) \
    {                              \
        foo_##num();               \
        return 0;                  \
    }
THREAD_DECLARE(one, sleep(-1))
THREAD_DECLARE(two, procA())
THREAD_DECLARE(three, sleep(-1))
THREAD_DECLARE(four, sleep(-1))
THREAD_DECLARE(five, sleep(-1))
#define THREAD_CREATE(num)                            \
    {                                                 \
        pthread_t threadID_##num;                     \
        pthread_create(&threadID_##num, NULL, thread_##num, NULL); \
    }
int main(int argc, const char *argv[])
{
    THREAD_CREATE(one)
    THREAD_CREATE(two)
    THREAD_CREATE(three)
    THREAD_CREATE(four)
    THREAD_CREATE(five)
    sleep(-1);
    return 0;
}

Loading the first core dump

We’ll start with loading the core dump App9.core.2.230:

gdb -c App9.core.2.230 -se App9

The above command will output the following to the terminal:

Identifying the largest memory

...