printf() debug is simple yet powerful when debugger is not available. We often insert printf() to trace all possible code path to find bug locations.

ccov automates this hard and time-consuming task.

It is an LLVM pass that inserts trace functions to the target at BasicBlock level. The trace function outputs execution log at runtime.

Let's assume collatz conjecture function.

void collatz(int n)
{
  while (n != 1) {
    if (n % 2 == 0) {
      n /= 2;
    } else {
      n = 3 * n + 1;
    }
  }
}

If you want to insert debug trace for all possible code-path, you have to add printf() like this:

void collatz(int n)
{
  printf("#1\n");
  while (n != 1) {
    printf("#2\n");
    if (n % 2 == 0) {
      printf("#3\n");
      n /= 2;
    } else {
      printf("#4\n");
      n = 3 * n + 1;
    }
    printf("#5\n");
  }
  printf("#6\n");
}

Even this function is quite simple, but there are six lines of insertions.

ccov make this process much easier. Only you have to do is, compile the target with ccov enabled.

$ clang -g -O0 -Xclang -load -Xclang ccov/build/CCov/libCCov.so -c -o main.o main.c

Note that ccov uses DebugLoc information in the LLVM bitcode. Becauses of this, you have to compile the source code with -g and -O0.

On runtime, the executable outputs traces.

#CCOV:main.c:collatz:10
#CCOV:main.c:collatz:18:ret
#CCOV:main.c:collatz:7:entry

This output is from __log_coverage() in sample/ccov.h. You can define your own trace output format. sample/report.py is an example script using ccov output.

    30|    10|  while (n != 1) {
    31|    18|}
    32|     7|void collatz(int n)

ccov requires __log_coverage() function with following prototype.

void __log_coverage(const char *file, const char *func, const int line, const int attr);

See sample/ccov.h for example definition.

• CMake 3.4.3 or later
• LLVM 9 or later

$ mkdir build
$ cd build
$ cmake ..
$ make

ccov is released under the MIT license.