Using fmgr_hook

Hello,
In the process of implementing my own version of sysdate, i was trying
to use the fmgr_hook.
I had a look at the sepgsql contrib module and tried to do the same by
modifying auto_explain just to test using fmgr_hook.

My code changes are:

static needs_fmgr_hook_type prev_needs_fmgr_hook = NULL;
static fmgr_hook_type prev_fmgr_hook = NULL;

static bool custom_needs_fmgr_hook(Oid functionId);
static void custom_fmgr_hook(FmgrHookEventType event,FmgrInfo *flinfo,
Datum *private);

in PG_init(void)
prev_needs_fmgr_hook = needs_fmgr_hook;
needs_fmgr_hook = custom_needs_fmgr_hook;
prev_fmgr_hook = fmgr_hook;
fmgr_hook = custom_fmgr_hook;

in _PG_fini(void)
needs_fmgr_hook=prev_needs_fmgr_hook;
fmgr_hook=prev_fmgr_hook;

static bool custom_needs_fmgr_hook(Oid functionId)
{
return true;
}
void custom_fmgr_hook(FmgrHookEventType event,FmgrInfo *flinfo, Datum *private)
{
if(flinfo->fn_extra == NULL)
{
TimestampTz current_timestamp = GetCurrentTimestamp();
flinfo->fn_extra = palloc(sizeof(TimestampTz));
flinfo->fn_extra = (void*) current_timestamp;
}
}

To debug i have a breakpoint inside custom_fmgr_hook.

Debugging:
1. Start postgres
2. Start psql connecting to postgres
3. Attach gdb to process spawned off by postmaster representing psql session.
4. execute select * from now();

Problem:
The breakpoint seems to get skipped. Just to be sure i put a
breakpoint in explain_ExecutorStart and i could debug that function.
So i am attaching gdb to correct process.
What am i doing wrong?

Thank you,
Sameer