refactor: move kernel build into independent Docker layer

Signed-off-by: Martin Kröning <[email protected]>

Dockerfile

@@ -1,4 +1,14 @@
-FROM rust:bookworm AS builder
+FROM --platform=$BUILDPLATFORM rust:bookworm AS kernel
+ADD --link https://github.com/hermit-os/kernel.git#hermit-c /kernel
+WORKDIR /kernel
+RUN cargo xtask build \
+    --artifact-dir . \
+    --arch x86_64 \
+    --release \
+    --no-default-features \
+    --features pci,smp,acpi,newlib,tcp,dhcpv4
+
+FROM buildpack-deps:bookworm AS builder
 
 RUN set -eux; \
     apt-get update; \
@@ -20,9 +30,9 @@ RUN set -eux; \
 
 WORKDIR /root
 
+COPY --link --from=kernel /kernel/libhermit.a ./kernel/libhermit.a
 ADD --link https://github.com/hermit-os/binutils.git binutils
 ADD --link https://github.com/hermit-os/gcc.git gcc
-ADD --link https://github.com/hermit-os/kernel.git#hermit-c kernel
 ADD --link https://github.com/hermit-os/newlib.git newlib
 ADD --link https://github.com/hermit-os/pthread-embedded.git pte
 ADD --link ./toolchain.sh ./toolchain.sh

toolchain.sh

@@ -69,15 +69,7 @@ make install-gcc
 cd -
 fi
 
-cd kernel
-cargo xtask build \
-    --artifact-dir . \
-    --arch x86_64 \
-    --release \
-    --no-default-features \
-    --features pci,smp,acpi,newlib,tcp,dhcpv4
-export LDFLAGS_FOR_TARGET=-L$PWD
-cd -
+export LDFLAGS_FOR_TARGET=-L/root/kernel
 
 if [ ! -d "tmp/newlib" ]; then
 mkdir -p tmp/newlib