CODEWITHSUNDEEP
clinuxunixperflinux-capabilities
ACCurrent
ACCurrent

Reputation: 385

How to use perf_evt_open to get seperate process's info

I've been trying to sample ptrace events from C. The following is my code to get a file handle on perf:

    pid_t pid;
    uint64_t next_offset=0;

    if(argc != 2) {
        fprintf(stderr,"please provide PID");
        exit(EXIT_FAILURE);
    }
    pid = atoi(argv[1]);
    printf("attaching to %d\n", pid);

    memset(&pe, 0, sizeof(struct perf_event_attr));
    pe.type = PERF_TYPE_SOFTWARE;
    pe.size = sizeof(struct perf_event_attr);
    pe.sample_type = PERF_SAMPLE_CPU | PERF_SAMPLE_TID;
    pe.config = PERF_COUNT_SW_CPU_CLOCK;
    pe.disabled = 1;
    pe.sample_freq = 99;
    pe.freq = 1;
    //pe.wakeup_events = 1;

    fd = perf_event_open(&pe, pid, -1, -1, 0);

Right now, if I set the pid to be a foreign process, I am not receiving any events. Yet, when I set the pid to be 0, I can read events from within my own process. I found the following line in the man pages for perf_event_open:

When pid is greater than zero, permission to perform this system call is governed by a ptrace access mode PTRACE_MODE_READ_REALCREDS check;

I would really appreciate some explanation of what this means.

PS: I've tried running the code as root AND my /proc/sys/kernel/perf_event_paranoid is -1. Command line perf works.

Upvotes: 0

Views: 90

Answers (0)

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