Uninitialised error detection when using fread about dcc HOT 2 CLOSED

So @Dylan-Brotherston has let me know that including unistd.h disables ASAN, but this is still detectable by valgrind, so would be good to turn that on when ASAN gets diabled?

$ dcc bug.c -o bug -fsanitize=valgrind
$ echo ABCD | ./bug
Runtime error: uninitialized variable accessed.

Execution stopped in main() in bug.c at line 11:

int main(int argc, char **argv) {
    char arr[5];
    fread(arr, 1, 4, stdin);
--> if (strcmp(arr, "ABCD") != 0) {
        printf("match\n");
    }
}

Values when execution stopped:

argc = 1
arr = "ABCD<uninitialized value>"

from dcc.

DCC has a list of "safe" includes here:

unistd.h isn't in that list because some functions provided by that header will case the dual sanitizers to become unsynchronized.

in this situation when compiling only one sanitizer will be included, by default sanitizer1 is the ASAN sanitizer and ASAN cannot detect this error, MSAN or Valgrind (usually sanitizer2) can detect this error.

Explicitly setting the first sanitizer to Valgrind with -fsanitize=valgrind fixes this issue, but then ASAN will not be running and other issues will be missed.

So currently this is intended behavior. best to run both dcc and dcc -fsanitize=valgrind separately in this case.

from dcc.