Free all memory allocated by LLVM on exit - c

Question

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?

Answer 1

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"