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I read through the post but I'm still a bit confused as to what parts of this is Zig and what parts are coming from other dependencies. What exactly is zig cc doing, and what does it rely on existing? Where are the savings coming from? Some people are mentioning that this is a clang frontend, so is the novelty here that zig cc 1. passes the the correct options to clang and 2. ships with recompilable support libraries (written in Zig, with a C ABI) to statically link these correctly (or, in the case of glibc, it seems to have some reduced fileset that it compiles into a stub libc to link against)? Where is the clang that the options are being passed to coming from? Is this a libclang or something that Zig ships with? Does this rely on the existence of a "dumb" cross compiler in the back at all?





To compile C code, you need a bunch of different things: headers for the target system, a C compiler targetting that system, and a libc implementation to (statically or dynamically) link against. Different libc implementations are compatible with the C standard, but can be incompatible with each other, so it's important that you get the right one.

Cross-compiling with clang is complex because it's just a C compiler, and doesn't make assumptions about what headers the target system might use, or what libc it's using, so you have to set all those things up separately.

Zig is (apparently) a new language built on Clang/LLVM, so it can re-use that to provide a C compiler. It also makes cross-compilation easier in two other ways. First, it limits the number of supported targets - only Linux and Windows, and on Linux only glibc and musl, and all supported on a fixed list of the most common architectures. Second, building Zig involves pre-compiling every supported libc for every supported OS and architecture, and bundling them with the downloadable Zig package. That moves a lot of work from the end user to the Zig maintainers.

Like most magic tricks there's no actual magic involved, it's just somebody doing more and harder work than you can believe anyone would reasonably do.


IIUC, libc are not prebuilt and bundled ("for every supported target combination"), "just" the source code of musl and glibc is bundled, and compiled lazily on your machine when first needed (i.e. for any target for which you invoke zig).

Does the LLVM toolchain that comes with Zig include cross-compilation support? Is that what it is using?

Yes.



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