Clang, Microsoft linker and standard library

Question

I have successfully built Clang with Microsoft C++ and I'm trying to get it to compile a hello world test case; it gets as far as generating an object file, linking with the standard library being the remaining stumbling block:

hello-202520.o : error LNK2019: unresolved external symbol _printf referenced in function _main
LINK : error LNK2001: unresolved external symbol _mainCRTStartup

There are comments from previous years saying Clang doesn't yet do Windows linking at all, but I get the impression those are outdated, and indeed it does now seem to be able to generate Windows format object files:

clang -c hello.c
ren hello.o hello.obj
link hello.obj

... doesn't barf, so the file format seems to be correct, but still gets the unresolved external symbol errors. Likely guess is the Microsoft compiler tags its output object files with an indication of the standard library they need to be linked with whereas Clang doesn't, and eyeballing a hex dump of the respective object files seems to confirm this and gives a hint of the linker command line to use:

link /defaultlib:libcmt /defaultlib:oldnames hello.obj

I had high hopes by this stage but alas it still gives the same unresolved external symbol errors.

What am I still missing?

Answer 1

Turns out Clang was by default generating 32-bit code but I was using 64-bit MSC, and the leading _ on C symbols has been dropped with the move to x64, so specifying -m64 on the clang command line did the job.