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 /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; \
@@ -15,6 +25,9 @@ RUN set -eux; \
 
 WORKDIR /root
 
+COPY --link --from=kernel /kernel/libhermit.a /root/kernel/libhermit.a
+ENV LDFLAGS_FOR_TARGET="-L/root/target/x86_64/release -lhermit"
+
 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/hermit-playground.git hermit

toolchain.sh

@@ -68,15 +68,6 @@ make install-gcc
 cd -
 fi
 
-cd kernel
-cargo xtask build \
-    --arch x86_64 \
-    --release \
-    --no-default-features \
-    --features pci,smp,acpi,newlib,tcp,dhcpv4
-export LDFLAGS_FOR_TARGET="-L$PWD/target/x86_64/release -lhermit"
-cd -
-
 if [ ! -d "tmp/newlib" ]; then
 mkdir -p tmp/newlib
 cd tmp/newlib