> But isn't it just uses an LLVM codegen, same as Swift or clang?
It's more complicated than that. I've been involved in a project (bootstrapping little-endian 32 bit PowerPC on linux) which needed a rust port. I didn't work on that, but from what I saw, it's at best a major nuisance, possibly a nightmare when something breaks. This may be a bad example since darwin/aarch64 is a more sane target, but still. ;-)
More importantly I guess, Firefox has some reeeeaally old platform specific cruft and some really rusty (hah!) ABI-glue stuff lying around. Stuff like the Netscape Portable Runtime. There's still code in Firefox from back when it ran on HP PA-RISC. There's even code for IBM Z mainframes in there. Really glossing over details, but there are some inner mechanisms that are very platform specific and need at least some custom code for each OS + CPU combo.
It's more complicated than that. I've been involved in a project (bootstrapping little-endian 32 bit PowerPC on linux) which needed a rust port. I didn't work on that, but from what I saw, it's at best a major nuisance, possibly a nightmare when something breaks. This may be a bad example since darwin/aarch64 is a more sane target, but still. ;-)
More importantly I guess, Firefox has some reeeeaally old platform specific cruft and some really rusty (hah!) ABI-glue stuff lying around. Stuff like the Netscape Portable Runtime. There's still code in Firefox from back when it ran on HP PA-RISC. There's even code for IBM Z mainframes in there. Really glossing over details, but there are some inner mechanisms that are very platform specific and need at least some custom code for each OS + CPU combo.