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[Libunwind-devel] ptrace-unwind not working at head

From: Humberto Abdelnur
Subject: [Libunwind-devel] ptrace-unwind not working at head
Date: Thu, 18 Feb 2010 18:13:50 +0100
User-agent: Thunderbird (X11/20090817)

Hello all,

I'm having some problems to unwind the IPs from a ptrace child.
Actually, using the version libunwind-0.99 it worked out.
Now that I move to the head version and the unwind IP is only one.
I did a tiniest poc (attached to the mail) so you can see the results.
The target application was opera.

After digging into the libunwind code I found that the problem was in the
file src/os-linux.h at line 269

if (!cp)
cp = scan_string (cp, NULL, 0);
if (!cp || dash != '-' || colon != ':')
continue; since scan_string with buf_size 0 always returns 0. So for me it does not make sense, does it?
So, i removed and it works well afterwards.

Now my real problem is when I call my upt_backtrace function (the one in the poc file) repetitively,
then the virtual memory of the process keeps increasing.
I do not know if i'm missing something in my code, but I realized that the mempool (src/mi/mempool.c) it does
a mmap but never a munmap.
I'm not quite sure where I should do the munmap (if it is that i m not getting confused), so can somebody help me out with it?

Thanks in advance,

Humberto Abdelnur

ps: Can you please put me in cc when replying as i m not registered in the mailing list

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <sys/types.h>

#include <libunwind.h>
#include <libunwind-ptrace.h>

void upt_backtrace(pid_t pid) {
    unw_addr_space_t as = unw_create_addr_space(&_UPT_accessors, 0);

    unw_word_t bt;

    void *upt = _UPT_create(pid);

    unw_cursor_t orig_cursor, curr_cursor;
    unw_init_remote(&orig_cursor, as, upt);
    curr_cursor = orig_cursor;

    int i = 0;
    do {
        unw_get_reg(&curr_cursor, UNW_REG_IP, &bt);
        printf("%lx\n", bt);
    } while (unw_step(&curr_cursor) > 0);


int main(int argc, char **argv) {
    pid_t pid = atoi(argv[1]);

    if (ptrace(PTRACE_ATTACH, pid, NULL, NULL)) {
       return 1;

    ptrace(PTRACE_DETACH, pid, NULL, NULL);
    return 0;

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