Codebase Analysis Lab

Sysprof is a “statisical, system-wide profiler for Linux”, and one of the packages in the pool for our group.

Beginning this lab, I had to start by installing fedpkg to perform the following commands:
fedpkg clone -a sysprof //move into the folder created; in this case “sysprof”
fedpkg prep //move into the “sysprof-1.2.0” folder.

Once all the files were in place, I started by searching for any files that ended with .s or .S: find $(pwd) | grep -i ".*\.s$" which returned nothing.

Next, I looked for the pattern “asm” inside all the files in the “sysprof-1.2.0” directory: grep "asm" * -r which resulted in:

TODO: /include/asm-i386/mach-default/do_timer.h. This function
util.h:#define rmb() asm volatile("lock; addl $0,0(%%esp)" ::: "memory")
util.h:#define cpu_relax() asm volatile("rep; nop" ::: "memory");
util.h:#define rmb() asm volatile("lfence" ::: "memory")
util.h:#define cpu_relax() asm volatile("rep; nop" ::: "memory");
util.h:#define rmb() asm volatile ("sync" ::: "memory")
util.h:#define cpu_relax() asm volatile ("" ::: "memory");
util.h:#define rmb() asm volatile("bcr 15,0" ::: "memory")
util.h:#define cpu_relax() asm volatile("" ::: "memory");
util.h:# define rmb() asm volatile("synco" ::: "memory")
util.h:# define rmb() asm volatile("" ::: "memory")
util.h:#define cpu_relax() asm volatile("" ::: "memory")
util.h:#define rmb() asm volatile("" ::: "memory")
util.h:#define cpu_relax() asm volatile("" ::: "memory");


The file TODO seemed to list a version history and not important to the requirement of this lab. However, the file util.h contained the following:

#ifndef UTIL_H
#define UTIL_H

#define FMT64 "%"G_GUINT64_FORMAT

#if defined(__i386__)
#define rmb() asm volatile("lock; addl $0,0(%%esp)" ::: "memory")
#define cpu_relax() asm volatile("rep; nop" ::: "memory");
#endif

#if defined(__x86_64__)
#define rmb() asm volatile("lfence" ::: "memory")
#define cpu_relax() asm volatile("rep; nop" ::: "memory");
#endif

#ifdef __powerpc__
#define rmb() asm volatile ("sync" ::: "memory")
#define cpu_relax() asm volatile ("" ::: "memory");
#endif

#ifdef __s390__
#define rmb() asm volatile("bcr 15,0" ::: "memory")
#define cpu_relax() asm volatile("" ::: "memory");
#endif

#ifdef __sh__
#if defined(__SH4A__) || defined(__SH5__)
# define rmb() asm volatile("synco" ::: "memory")
#else
# define rmb() asm volatile("" ::: "memory")
#endif
#define cpu_relax() asm volatile("" ::: "memory")
#endif

#ifdef __hppa__
#define rmb() asm volatile("" ::: "memory")
#define cpu_relax() asm volatile("" ::: "memory");
#endif

#endif


This file exemplifies the purpose of this course. The assembly language is so particular to a processor architecture that lines of code are needed for each architecture. In this case, there are logic statements for 32-bit x86, 64-bit x86, powerPC, IBM ESA/390, SuperH (for models 4 and 5, and then the rest), and finally for HP’s Precision Architecture. The purpose of memory barriers are to ensure specified operations, before and after, are executed in a predictable manner.

While my exposure to memory barriers is extremely limited, but doing a cursory look at memory barriers, it does seem there are solution in both the aarch64 and with c/c++; the latter could remove the architecture dependencies.

The second package we looked at was oprofile, a system-wide profiler for Linux systems. Following a similar search pattern for sysprof, I was unable to find any files ending with .s. However, checking for asm resulted in this. The inline assembly found in libperf_events/operf_utils.h looks similar to the assembly found in sysprof. Looking closer at the entire file (click on link), we can see it has a similar structure to the file found in sysprof, but also having additional lines for additional architectures – including arm and aarch64.

The other files, with the exception of op_hw_specific.h, contained the pattern “asm” as text, in the code descriptor. Taking a closer look at op_hw_specific.h (click on link), looks like a list of functions written in assembly to gather information on the processor properties of the system. With some changes to the syntax of register references, it should not be difficult to make this code adaptable for aarch64.