Hi *, I have been playing with perf-probe tool and I found out that some bogus values of a function argument are obtained by perf-record.
How to reproduce: gcc -O0 -g -o dummy dummy.c perf probe -x ./dummy --add 'isprime a' perf record -e probe_dummy:isprime ./dummy perf script The actual output looks like the following: dummy 32476 [000] 3534401.838454: probe_dummy:isprime: (400530) a=32767 dummy 32476 [000] 3534401.838504: probe_dummy:isprime: (400530) a=32714 dummy 32476 [000] 3534401.838513: probe_dummy:isprime: (400530) a=3 dummy 32476 [000] 3534401.838519: probe_dummy:isprime: (400530) a=4 dummy 32476 [000] 3534401.838525: probe_dummy:isprime: (400530) a=5 dummy 32476 [000] 3534401.838531: probe_dummy:isprime: (400530) a=6 dummy 32476 [000] 3534401.838537: probe_dummy:isprime: (400530) a=7 dummy 32476 [000] 3534401.838543: probe_dummy:isprime: (400530) a=13 dummy 32476 [000] 3534401.838561: probe_dummy:isprime: (400530) a=17 But if you look into the source, you can see that the function isprime() is called with the following arguments: int numbers[] = { 2, 3, 4, 5, 6, 7, 13, 17, 19 }; So the first and last ones are omitted, there are some bogus numbers instead of them and all that is shifted somehow. Note that when I probe for %ax register it looks correct. The version of kernel/perf is 4.3.0. The architecture is x86_64. Am I missing something or is it a bug? Thank you! Michael
#include <stdlib.h> #include <stdio.h> int isprime(int a) { int i; if(a <= 1) return 0; for(i = 2; i <= a / 2; i++) if(!(a % i)) return 0; return 1; } int main(int argc, char **argv) { int numbers[] = { 2, 3, 4, 5, 6, 7, 13, 17, 19 }; int i; for(i = 0; i < 9; i++) { printf("%i %s prime\n", numbers[i], (isprime(numbers[i]))? "is" : "is not"); } return 0; }