On Mon, Sep 18, 2023 at 9:38 AM Matthew Maurer <mmaurer@xxxxxxxxxx> wrote: > > On Mon, Sep 18, 2023 at 8:25 AM Nick Desaulniers > <ndesaulniers@xxxxxxxxxx> wrote: > > > > What happens if you invoke the linker directly? > Rust unfortunately currently doesn't support invoking the linker > directly: https://github.com/rust-lang/rust/issues/73632 Wait; does Rust have its own linker? It doesn't use the system linker? Perhaps that's necessary for the rust module format? If so, TIL. > > Generally, the kernel either invokes the compiler or the linker > > directly. (For assembler, it is typically preprocessed, as are linker > > scripts!) So invoking the linker directly is a common pattern in > > kbuild. It also makes me slightly sad if the rust compiler ends up > > invoking a c compiler, even if it's simply to drive the linker. > As mentioned earlier, we could pass $HOSTLD, but if the linker isn't > named something accurate (e.g. if the linker is not named lld, but is > lld), we need to know how to pass a flavor: > https://doc.rust-lang.org/rustc/codegen-options/index.html#linker-flavor > Would it be appropriate to just assume the linker is named correctly? If it were not, what does failure look like? command not found: asdfadfasdf Seems fine to me. If the user mis-specifies HOSTLD=, then they will get a similar error, which should be prescriptive enough for them to figure out how exactly they're "holding it wrong." > > For example, Android carries a downstream patch to set `-fuse-ld=lld` > > for $KBUILD_HOSTCFLAGS, because its build environment doesn't contain > > GNU binutils ("guilty, officer"). > Oddly, the Android kernel environment (Kleaf) is the one that I needed > this patch to build in, but it seemed to be working without a manual > KBUILD_HOSTCFLAGS forwarding. Surprising that worked. > Overall, it sounds like you'd prefer if I set this to use > `KBUILD_HOSTLD` and `KBUILD_HOSTLDFLAGS`, and leave the linker flavor > to autodetect? Yes for the first two. Dunno, what precisely is a linker flavor? Is that like a flavor of ice cream? Oh, right looking at your link: https://doc.rust-lang.org/rustc/codegen-options/index.html#linker-flavor Seems like if `LLVM=1` is set, or `LD=ld.lld`, or CONFIG_LD_IS_LLD, then the flavor should be set to ld.lld, else ld. Then the KBUILD_HOSTLDFLAGS need to be passed, probably. But how are there "linker flavors" like ld or ld.lld if you just said "Rust unfortunately currently doesn't support invoking the linker directly: https://github.com/rust-lang/rust/issues/73632";. I'm having trouble reconciling the two. Can we do something more like the below? ifdef CONFIG_LD_IS_LLD hostrust_flags += -C linker-flavor=ld.lld else hostrust_flags += -C linker-flavor=ld endif hostrust_flags += -C linker=$(HOSTLD) <todo: figure out how to pass KBUILD_HOSTLDFLAGS> -- Thanks, ~Nick Desaulniers
