Cedo (constexpr dot o)

cedo is a tool for creating object files from state at runtime. cedo exists to solve the same problem as the constexpr or the more recent and more apt keyword consteval. cedo can be used as part of a projects build to create state at compile time that cannot be computed by constexpr. The inital idea was inspired after std::embed failed to make it into the C++20 standard.

Example

We can use linkers to embed files or any arbitrary data into an object file. cedo however goes a step beyond it reads the debugging symbols of the program it runs to export any arbitrary data object.

githash.c

char githash[41];

int main() {
    // Find current git hash and fill in githash
}

This can be build like clang githash.c -shared -g -o export_githash Then we can run cedo export_githash -s githash -S -o githash.s . This will run the program export_githash and on it's exit serialize the symbol githash, -S says to output an assembly file, just like it does with cc. It then create an according assembly file githash.s. We can then use this file with our build has we would like. githash.s might look like:

githash.s

    .file   "export_githash"
    .global githash
    .data
    .align  32
    .type   githash, @object
    .size   githash, 41
githash:
    .asciz  "d670460b4b4aece5915caf5c68d12f560a9fe3e4"

    .ident  "cedo 1.0 (e5b3985af804eb658a78d5546915ba8bfb256884)"

Obviously, something like a git hash is trivial enough that we can rely on the linker. However cedo with the help of debug symbols can serialize arbitrarily complicated data objects into object files.

A similar example can be found in src/version where cedo bootstraps itself to provide it's own verison info.

Building

mkdir build; cd build; cmake ..

Testing

cd build/test/; ctest

For running unit tests under the /test/unittest directory, the llvm utility yaml2obj is required.