Problems on glibc UTRACE

[Shane Wayne <zx0319 at gmail dot com>]

I've recently tap into malloc function of glibc, but I've encounter
some problems.
Firstly, I have install systemtap and glibc-dbg on Ubuntu 14.04(with
kernel 3.13 and UTRACE kernel flag default on).
The result show that, I can tap into
process("/lib/x86_64-linux-gnu/libc.so.6").function("malloc"), BUT,
the question is that, I can't get the right $bytes in this system, the
value I've got always like an pointer value start with 0x7f****. I've
tried the script on my own micro benchmark, with a single malloc
function invoke, the result also show that I can't get the right
parameters out, what's more, my micro benchmark triggered the tap
TWICE.
Secondly, I migrate to CentOS 6.6, with kernel
2.6.32-504.1.3.el6.x86_64 and UTRACE kernel flag default on, at this
time, I can get the right parameter $bytes out, but in my own micro
benchmark, the twice triggered problem also appear.