Free all memory allocated by LLVM on exit

user_2971847 0
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I am using LLVM-C to program a little toy language. I am using also valgrind to check for memory leaks.

Here is my basic baby program:

#include <stdio.h>
#include <llvm-c/Core.h>

int main()
{
    size_t length;
    LLVMModuleRef module = LLVMModuleCreateWithName("llvm.hello");
    printf("Module name: %s\n", LLVMGetModuleIdentifier(module, &length));
    LLVMDisposeModule(module);
    LLVMShutDown();
    return 0;
}

I can compile and run the program normally, as expected. However when I run the program through valgrind, it tells me I have some "still reachable" allocated memory like this.

valgrind  --leak-check=full  out/hello_llvm

==5807== LEAK SUMMARY:
==5807==    definitely lost: 0 bytes in 0 blocks
==5807==    indirectly lost: 0 bytes in 0 blocks
==5807==      possibly lost: 0 bytes in 0 blocks
==5807==    still reachable: 56 bytes in 2 blocks
==5807==         suppressed: 0 bytes in 0 blocks

While searching over here on this site for an answer, I found many coders are saying that "still reachable" memory leaks are not such a big deal. I don't want to argue about that. What I want is to get rid of ALL allocated memory before terminating my program.

Is there any way I can reduce that allocated memory down to zero before termination?

llvm memory-leaks valgrind c
1 Answers

It also makes me very nervous when valgrind does not give 0, in those cases I create a suppression file, if you want to give it a try:

Create and compile a minimal test:

> cat demo.c
#include <stdlib.h>

int main(void)
{
    malloc(10); // leak
}

Create a supression file:

valgrind --leak-check=full --show-reachable=yes --error-limit=no --gen-suppressions=all --log-file=minimal.supp ./demo

Edit the generated minimal.supp file, you will see something like

==3102== Memcheck, a memory error detector
==3102== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3102== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==3102== Command: ./demo
==3102== Parent PID: 2633
==3102== 
==3102== 
==3102== HEAP SUMMARY:
==3102==     in use at exit: 10 bytes in 1 blocks
==3102==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
==3102== 
==3102== 10 bytes in 1 blocks are definitely lost in loss record 1 of 1
==3102==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==3102==    by 0x10915A: main (in /home/david/demo)
==3102== 
{
   <insert_a_suppression_name_here>
   Memcheck:Leak
   match-leak-kinds: definite
   fun:malloc
   fun:main
}
==3102== LEAK SUMMARY:
==3102==    definitely lost: 10 bytes in 1 blocks
==3102==    indirectly lost: 0 bytes in 0 blocks
==3102==      possibly lost: 0 bytes in 0 blocks
==3102==    still reachable: 0 bytes in 0 blocks
==3102==         suppressed: 0 bytes in 0 blocks
==3102== 
==3102== For lists of detected and suppressed errors, rerun with: -s
==3102== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

Remove all the lines starting with == and save something like:

{
   <my stupid external LLVM leak>
   Memcheck:Leak
   match-leak-kinds: definite
   fun:malloc
   fun:main
}

Now run valgrind with the supression file:

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --error-limit=no --suppressions=minimal.supp ./demo

The result is:

==3348== Memcheck, a memory error detector
==3348== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3348== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==3348== Command: ./demo
==3348== 
==3348== 
==3348== HEAP SUMMARY:
==3348==     in use at exit: 10 bytes in 1 blocks
==3348==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
==3348== 
==3348== LEAK SUMMARY:
==3348==    definitely lost: 0 bytes in 0 blocks
==3348==    indirectly lost: 0 bytes in 0 blocks
==3348==      possibly lost: 0 bytes in 0 blocks
==3348==    still reachable: 0 bytes in 0 blocks
==3348==         suppressed: 10 bytes in 1 blocks
==3348== 
==3348== For lists of detected and suppressed errors, rerun with: -s
==3348== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1 from 1)

As you can see, the leak is moved from "definitely lost" to "suppressed"

user_16063450
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