PLT hook segfault about GCC 7

[withgit-contributor]

There is no this problem of uftrace built by gcc 5.4.1.
But when building uftrace by gcc 7.0.1, I found the segmentation fault about PLT hook like below.

# normal tracing

$ uftrace tests/t-abc
WARN: invalid task file
child terminated by signal: 11: Segmentation fault
# DURATION    TID     FUNCTION

But if using --no-libcall, the segmentation fault didn't appear.

$ uftrace --no-libcall t-abc
# DURATION    TID     FUNCTION
            [ 5133] | main() {
            [ 5133] |   a() {
            [ 5133] |     b() {
   0.982 us [ 5133] |       c();
   1.854 us [ 5133] |     } /* b */
   2.170 us [ 5133] |   } /* a */
   2.792 us [ 5133] | } /* main */

If checking core file, you can see libmcount/plthook.c:429

Reading symbols from t-abc...(no debugging symbols found)...done.
[New LWP 5249]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `t-abc'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007ff5a1b8a322 in plthook_entry (ret_addr=0x7ffd79fb0378, child_idx=1, 
    module_id=140692961395048, regs=0x7ffd79fb0338)
    at /home/taeung/git/uftrace/libmcount/plthook.c:429
429		struct ftrace_trigger tr = {