Execution Model

Files Created by Compilation

Gnatmake creates the following files

Library Information file (eg sayhi.ali): describes when compilation occurred and any file dependencies

Object file (eg sayhi.o): contains non-executable machine code, but does not contain code for library routines)

Executable file (sayhi.exe in Windows, sayhi in linux): executable machine code (all libraries are linked in)

The .ali and .o files are not needed after the executable is created.

Linux/Windows Difference: Different Extension for Executable

Windows executable is sayhi.exe

Linux executable is sayhi

sayhi.exe can be run using either sayhi or sayhi.exe

Ada/Java Difference: Case Sensitivity

The java language is case sensitive, Ada is not

Linux is case sensitive, windows is not

The commands javac and java are case sensitive (even in windows)

The command gnatmake expects the filename to be in LOWER CASE (in both windows and linux)

Linux/Windows Difference: Executables are not Compatible

Object files and executable files are platform specific.

Such files created on one platform (eg rucs) will not run on another platform (eg Intel machines in unix lab)

If you switch systems you must recompile, as follows: either

Delete all .o and executable files, then recompile
Or, if the files are up to date, force recompilation with -f flag (gnatmake -f sayhi)

This is more of a problem when your program has multiple files so that when you switch systems you end up with files compiled under different systems

Different from java: class files will run on any machines. Why?

Ada/Java Difference: Interpretation vs Direct Execution

In Java, javac Hi.java creates file Hi.class file which you interpret with java Hi

java Hi runs the interpreter on the hardware. The interpreter takes Hi.class as input and interprets (ie executes) the instructions in Hi.class

Hi.class contains java byte code

In Ada, gnatmake sayhi creates the executable sayhi.exe which runs directly on the hardware