Delphi Compile and Build produce different binary on same project

Question

In a fresh VCL application Compile and Build operation produce the same binary and map file (with minor differences at the end of .exe file

Answer 1

If you use compiler defines in your project and just changed those, if you do a compile, you won't see any changes to the dcu's and the resulting module (exe or dll). If you do a full rebuild the compiler defines are used in the newly created dcu's and modules.

I have seen this in a large project group where we use modules in different projects with different defines and all dcu's are stored in the same directory.

Ergo: The compiler does not enforce the dependancies on the defines in this case.

Perhaps you did see the same issue.

Answer 2

There is two parts to this answer I believe.

Part of the problem your seeing, IIRC, is that the compiler doesn't zero out memory before doing a compile/build. Thus anything left in uninitialized memory becomes filler in the output for alignment purposes.

I also seem to recall that there is a date time stamp included in the pe header information for the application. that will cause a difference every time.

I'm not the best person to confirm this but this is what I seem to recall from past discussions.

People like Allen Bauer or Barry Kelly would probably be able to give better/more accurate information on this.

Answer 3

What you're seeing is simply an artifact of the built-in make logic of the compiler. When you do a build, it tells the compiler to build all available sources. So Delphi processes each source file and for each unit in the uses lists for which it finds source, it will then build that file. It does this recursively. When you do a compile, only the existing .dcu files are loaded and if they're found to be up-to-date, nothing is done. This can actually lead to a different order in which the units are discovered since each .dcu will effectively "flatten" the uses list. Since the units are discovered and loaded in a different order, they are in-turn, linked in a different order. This is why your map files look so different. Given the same sources, the map file should be the same if you do two builds in a row or two compiles in a row.

Other causes for differences are more mundane and include things like the PE header time stamp, and other bits of padding and alignments.