I've been known to dabble in assembly language from time to time, and there's been this one instruction on the Intel Pentium that I've wanted to play around with—RDTSC (Read Time-Stamp Counter). It's used to read the internal time-stamp counter which is incremented every clock cycle. On my system, this counter is incremented 2,660,000,000 times per second (the computer is running at 2.66GHz (Gigahertz)) and this makes for a nice way to time code, as the instruction is available in userspace (at least on Linux).
I wanted to use this to time some Lua code [1], which means I need to wrap this instruction into a function that can be called. I could have used some inline assembly in C to do this, but
It wasn't hard:
;***************************************************************************
;
; Copyright 2020 by Sean Conner.
;
; This library is free software; you can redistribute it and/or modify it
; under the terms of the GNU Lesser General Public License as published by
; the Free Software Foundation; either version 3 of the License, or (at your
; option) any later version.
;
; This library is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
; or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
; License for more details.
;
; You should have received a copy of the GNU Lesser General Public License
; along with this library; if not, see <http://www.gnu.org/licenses/>.
;
; Comments, questions and criticisms can be sent to: sean@conman.org
;
;***************************************************************************
bits 32
global luaopen_rdtsc
extern lua_pushinteger
extern lua_pushcclosure
;***************************************************************************
section .text
ldl_rdtsc: rdtsc
push edx
push eax
push dword [esp + 12]
call lua_pushinteger ; lua_pushinteger(L,rdtsc);
xor eax,eax ; return 1
inc eax
lea esp,[esp + 12]
ret
;---------------------------------------------------------------------------
luaopen_rdtsc:
xor eax,eax
push eax
push ldl_rdtsc
push dword [esp + 12]
call lua_pushcclosure ; lua_pushcclosure(L,ldl_rdtsc,0);
xor eax,eax ; return 1
inc eax
lea esp,[esp + 12]
ret
I'll leave it up to the reader to convert this to 64-bit code.