How to always produce byte-for-byte identical .exe on rebuild of C# application?

Question

I\'ll give you a little bit of background first as to why I\'m asking this question:

I am currently working in a stricly-regulated industry and as such our code is quite

Answer 1

Update: Roslyn seems to have a /feature:deterministic compiler flag for reproducible builds, although it's not 100% working yet.

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You should be able to get rid of the debug GUID by disabling PDB generation. If not, setting the GUID to zeroes is fine - only debuggers look at that section (you won't be able to debug the assembly anymore, but it should still run fine).

The PrivateImplementationDetails are a bit more difficult - these are internal helper classes generated by the compiler for certain language constructs (array initializers, switch statements using strings, etc.). Because they are only used internally, the class name doesn't really matter, so you could just assign a running number to them.

I would do this by going through the #Strings metadata stream and replacing all strings of the form "{GUID}" with "{running number, padded to same length as a GUID}".

The #Strings metadata stream is simply the list of strings used by the metadata, encoded in UTF-8 and separated by \0; so finding and replacing the names should be easy once you know where the #Strings stream is inside the executable file.

Unfortunately the "metadata stream headers" containing this information are quite buried inside the file format. You'll have to start at the NT Optional Header, find the pointer to the CLI Runtime Header, resolve it to a file position using the PE section table (it's an RVA, but you need a position inside the file), then go to the metadata root and read the stream headers.