Different object code generated each time file is compiled

[Burt Bicksler <bbicksler at fortresstech dot com>]

Hi,

We are build for a MIPS32 target using a GCC cross compiler, and we have 
two object files that are always different each time they are built with 
no changes to the source code.  We have used the -E switch to generate 
pre-processor output and compared the pre-processor output from each run 
against each other.

They pre-processor output from each run is the same.  So it appears for 
these two source files that the issue with the object code being 
generated differing comes from the compiler.  It is the object files 
before linking that are different (as well as the resulting final 
binaries but we have tracked it back to the object files emitted by the 
compiler as the first point where the files differ.

It is only two source files that we see this difference with and it is 
always 4 bytes in each object file that is different.

Has anyone encountered anything like this before?

Note that the resulting code always seems to execute just fine.  This 
would not be an issue except that we have a requirement to be able to 
validate that the code produced from a given revision of the source code 
always produces a binary identical executable, and this issue is causing 
some head scratching.

Thanks,
Burt