sanitizer-leak is NOT detected when golang using cgo to call c library

Question

Summary

Previously I used clang-3.8.1 and sanitizer is crashed when using AddressSanitizer. And leakSanitizer doesn't work at all.

Then I try to use clang-llvm-10.0, AddressSanitizer could detect the address issue and work normally.

But leak issue can NOT be detected when golang using cgo to call C. Is it possible to use leak-sanitizer to detect memory leak issues in C/C++ libs when golang using CGO?

Example

• cgo-sanitizer.go: address issue is detected expectedly.

package main

// #include <stdlib.h>
//
// int test()
// {
//   int *p = (int *)malloc(10 * sizeof(int));
//   free(p);
//   p[1] = 42;
//   return p[1];
// }
import "C"
import "fmt"

func main() {
  fmt.Println(int(C.test()))
  // Output: 42
}

• Output

[root@380c7770b175 cplusplus]# CC="clang" CGO_CFLAGS="-O0 -g -fsanitize=address" CGO_LDFLAGS="-fsanitize=address" go run cgo-sanitizer.go
=================================================================
==25680==ERROR: AddressSanitizer: heap-use-after-free on address 0x604000000014 at pc 0x00000054fc2d bp 0x7ffd96a943b0 sp 0x7ffd96a943a8
WRITE of size 4 at 0x604000000014 thread T0
    #0 0x54fc2c in test (/tmp/go-build237509829/b001/exe/cgo-sanitizer+0x54fc2c)
    #1 0x54fcc1 in _cgo_a3187169dba5_Cfunc_test (/tmp/go-build237509829/b001/exe/cgo-sanitizer+0x54fcc1)
    #2 0x5159df  (/tmp/go-build237509829/b001/exe/cgo-sanitizer+0x5159df)

• cgo-sanitizer-leak.go: leak issue was not detected. Why?

package main

// #include <stdlib.h>
//
// int *p;
// int test()
// {
//   p = (int *)malloc(10 * sizeof(int));
//   p = 0;
//   return 52;
// }
import "C"
import "fmt"

func main() {
  fmt.Println(int(C.test()))
  // Output: 52
}

[root@380c7770b175 cplusplus]# CC="clang" CGO_CFLAGS="-O0 -g -fsanitize=leak" CGO_LDFLAGS="-fsanitize=address" go run cgo-sanitizer-leak.go
52

Environment

[root@380c7770b175 cplusplus]# cat /proc/version
Linux version 3.10.0-493.el7.x86_64 ([email protected]) (gcc version 4.8.5 20150623 (Red Hat 4.8.5-9) (GCC) ) #1 SMP Tue Aug 16 11:45:26 EDT 2016

[root@380c7770b175 cplusplus]# clang -v
clang version 10.0.0
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/llvm-10.0/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64

[root@380c7770b175 cplusplus]# go version
go version go1.13.6 linux/amd64

Original question

https://github.com/google/sanitizers/issues/1223

Answer 1

I have solved it by explicitly calling __lsan_do_leak_check(), when process exiting.

__lsan_do_leak_check() is declared in

https://github.com/llvm/llvm-project/blob/master/compiler-rt/include/sanitizer/lsan_interface.h

I guess it's related to c-main start mechanism and __lsan_do_leak_check() is not registered for golang start.

Welcome anyone who could continuously dig on it.

Answer 2

@Shawn is correct that you need to invoke __lsan_do_leak_check manually if your main program is written in Go. If your main is in C/C++ and Go is invoked as a library then it's not needed.

Here is a simple example

package main

// #include <stdio.h>
// #include <stdlib.h>
//
// void __lsan_do_leak_check(void);
//
// void leak_a_bit(void)
// {
//     char* p = malloc(2000);
//     printf("%p\n", p);
// }
import "C"

func main() {
        C.leak_a_bit()

        C.__lsan_do_leak_check()
}

Compile and run like this

$ CC=clang CGO_ENABLED=1 CGO_LDFLAGS='-fsanitize=address' CGO_CFLAGS='-fsanitize=address' go build -o main

$ ./main