the example showcases the use of the simulator SimIt-ARM v. 2.1 both for the analysis of the executable and for the command-line simulation of a program for GCD computation with Euclid's algorithm (Listing 7.11 in (Schaumont, 2012))

• version 2.1 of the simulator is made use of, rather than the current 3.0, because the former supports cycle-accurate simulation, whereas the latter only supports functional simulation

compilation goes through the cross-compiler arm-linux-gcc, for ISA ARMv5, implemented in the StrongARM processor among others

• this cross-compiler with related binary utilities as well as the simulator can be found in repository rijndael.ece.vt.edu/gezel2repo

archive arm_simitarm_example.tgz, available in folder crosstools of the reserved lab area, provides two scripts for this tutorial:

• arm-linux-gccToolchain.sh for the production of assembly source, object file and executable
• sim/SimIt-ARM.sh for cycle-accurate analysis of the execution (simulator sima) and for simulation with the ema debugger, with command-line input in file emadCommands.txt

the example deals with the execution, on an ARM Cortex-A9 in the Altera DE1-SoC system, of a variation of the program in Listing 7.1, where the main() function body is replaced by

• printf("maxgcd(a,b)=%d\n", gcd(a,b));
  return 0;

loading and execution take place by means of the program altera-monitor-program, under control of its included GDB debugger and through the JTAG connection between the program and the DE1-SoC

• the system allows the loading of a C or assembly source, whereby compilation is done through the monitor program itself, however, in this example, scripts are provided that are similar to those in the previous examples, in order to allow low-level analysis with binary utilities, and the executable is loaded that is generated by those scripts

the archive arm_cortex-a9_example.tgz, available in the crosstools folder of the reserved lab area contains the following scripts:

• arm_altera_gccToolchain.sh for the production of assembly source, object and executable
• ext_build/arm_altera_gcc_extToolchain.sh for the analysis of the object and executable files

the same C source from the previous example may be compiled and executed by a NIOS II softcore on the FPGA of the DE1-SoC system, in this example with no other script, just to explore the use of the debugger included in the monitor program

run the scripts provided with this tutorial, examine the files produced by their execution, find a few not well-known aspects of their contents, search the web for information about them and produce some tutorial documentation in form of a list of questions and answers

• each answer should give a reference to its source; if the answer is drawn from a directly accessible web source, insert the specific link; if this points to information that only answers the question, then giving the link as answer is enough

here are three examples of question and answer, one for each of the three types described above:

• Q: What is the meaning of the acronyms VMA and LMA in the output of objdump?
• A: Respectively virtual memory address and load memory address; the former is the address of a program section during execution, the latter is its address when the program is first loaded in memory; the two addresses may differ when the program is first loaded on a different memory than the one which holds it at runtime, for example it is loaded on a Flash memory and then copied into RAM when it executes. (Schaumont, 2012, pp. 216-217)
• Q: What does the ARM instruction rsb do?
• A: It stands for reverse subtract, as it subtracts the first source operand from the second one, that is, the two arguments are in reverse order with respect to sub; please note that arithmetic ARM instructions allow the second source operand to be immediate, whereas the first one and the destination must be registers, so this instruction allows subtraction from a constant. (www.heyrick.co.uk/armwiki/RSB)
• Q: What is the origin of the name bss of the executable program section that contains the global variables?
• A: en.wikipedia.org/wiki/.bss#Origin

recommended readings:

• Schaumont (2012) Ch. 7, Sect. 7.4, 7.6.2

readings for further consultation:

• Schaumont (2012) Ch. 7, Sect. 7.6.1, 7.6.3

useful materials for the proposed lab experience:

• GCC, the GNU Compiler Collection
• GNU Binary Utilities
• Introduction to the the Altera Nios II Soft Processor, Altera University Program, May 2016
• Introduction to the ARM® Processor Using Altera Toolchain, Altera University Program, May 2016
• SimIt-ARM Users' Guide
• Altera Monitor Program Tutorial for Nios II, Altera University Program, May 2016
• Altera Monitor Program Tutorial for ARM, Altera University Program, May 2016