On Windows MSVC, is it possible to merge some .obj into one .obj? If yes, how should I do that?

Question

For example, there is three object files a.obj b.obj c.obj just compiled out with cl, and it is desired to combine them into one combined.obj.

A comment of an SO question points out that on *nix it's possible to do this kind of thing with ld. However, cl and link all seems only support .exe, .dll and .lib as output.

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The whole procedure of what I want to do with the combined object file as follows:

1. a.obj b.obj c.obj -> combined.obj
2. combined.obj d.obj e.obj -> executable.exe

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My problem is solved. a.obj b.obj c.obj use some variables and functions yet to be linked, and I thought that .lib can't tolerant missing functions since it is a library, but in fact it is OK. I can just merge them into an .lib file:

lib *.obj /OUT:combined.lib

Answer 1

Seems not, but it is convenient to merge them into an .lib:

lib *.obj /OUT:combined.lib

Answer 2

You can apply the method employed here also to the COFF files created by cl.exe, provided that your build of ld supports the respective input and output formats and those formats lend themselves to the process.

What you can do in such a case is this (and yes $INPUTS means you can give multiple object files as you wanted):

ld --oformat pe-x86-64 -r $INPUTS -o $OUTPUT

The --oformat pe-x86-64 (aka AMD64, x64 on Windows) is necessary whenever the ld has been built with a different default output format.

If that's the case and you didn't give --oformat you will get something like:

ld: relocatable linking with relocations from format pe-x86-64 (input.obj) to format elf64-x86-64 (output.obj) is not supported

However the process doesn't work for all input/output format combinations, as I learned with ld 2.34 on Ubuntu 20.04:

ld: relocatable linking with relocations from format pe-i386 (input.obj) to format pe-i386 (output.obj) is not supported

NB: At this point I had no luck to get this to work with lld-link or ld.lld (both available through modern VS versions), though.