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Introduction
Background
A programmer's goal is to write correct, efficient code. Code must
initially be written with the goal of being correct. Once correctness
has been established, programmers generally strive to make their code as
efficient as possible. This project focuses on
creating more efficient code through the use of profiling tools.
Execution profiling tools are a great asset to programmers creating
efficient code. Profiling tools can give programmers insight into what
functions are being called and how much time is spent in
each during a program's execution. This information can be used to
identify bottlenecks in a program that may be a good candidate for
reexamination to improve efficiency. One such tool in common use is
Gprof.
Problem Statement
Currently, Gprof instruments source code at compile time and tracks
what functions were called, how many times each function was called, how
long was spent in each function, and a call graph (what function called
the function in question). Profiling with Gprof
entails the following steps:
1. Compile your source code with the -pg option
2. Run your binary file (during this stage a gmon.out file will be
generated containing profiling information)
3. Examine the profile information by running Gprof on the gmon.out file
The current framework that Gprof uses may be too restrictive for certain
profiling activities. Gprof requires that the source code be recompiled
with the -pg option specified in order for profiling instrumentation to
take place. This can be too restrictive in the event that (1) only the
binary is available (the source code is not accessible), (2) compilation
time is prohibitively long, or (3) the programmer wishes to instrument
dynamic libraries for profiling that the program calls during execution.
We propose creating a tool for binary instrumentation of Gprof
profiling.
Design
We set out to create a tool that inserts instrumentation for Gprof
profiling into arbitrary binaries. Dyninst provided the means for adding
additional code to an already compiled binary. We extracted the code
used by the Gnu C Compiler when the -pg option was
specified and inserted it into arbitrary binaries. When source code
compiled with the -pg is run, we discovered that “mcount” is called at
the beginning of each function in the program. At the end of execution,
the final call to mcount generates the gmon.out file that contains Gprof
profiling data. In order to reproduce the gmon.out file for code
compiled without the -pg option, we used Dyninst to insert calls to
mcount at the beginning of each function. See the Methodology section
for more information. |
