fix: use architecture-specific build stages

Author: dottorblaster

scx_rustland/Dockerfile

@@ -1,3 +1,4 @@
+ARG BUILDARCH
 FROM rust:1.87-slim AS builder
 
 ADD https://github.com/sched-ext/scx.git /scx
@@ -30,21 +31,22 @@ RUN rustup component add rustfmt
 
 RUN cargo build --release -p scx_rustland
 
-FROM gcr.io/distroless/cc
+FROM alpine AS libs-amd64
+COPY --from=builder /usr/lib/x86_64-linux-gnu/libelf.so.1 /usr/lib/libelf.so.1
+COPY --from=builder /usr/lib/x86_64-linux-gnu/libz.so.1 /usr/lib/libz.so.1
+COPY --from=builder /usr/lib/x86_64-linux-gnu/libseccomp.so.2 /usr/lib/libseccomp.so.2
 
-ARG TARGETPLATFORM
+FROM alpine AS libs-arm64
+COPY --from=builder /usr/lib/aarch64-linux-gnu/libelf.so.1 /usr/lib/libelf.so.1
+COPY --from=builder /usr/lib/aarch64-linux-gnu/libz.so.1 /usr/lib/libz.so.1
+COPY --from=builder /usr/lib/aarch64-linux-gnu/libseccomp.so.2 /usr/lib/libseccomp.so.2
 
-RUN if [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
-      echo "Setting $COPY_LIBS_DIR to aarch64-linux-gnu" && \
-      export COPY_LIBS_DIR="aarch64-linux-gnu"; \
-    else \
-      echo "Setting default COPY_LIBS_DIR x86_64-linux-gnu" && \
-      export COPY_LIBS_DIR="x86_64-linux-gnu"; \
-    fi
+FROM libs-${BUILDARCH} AS libs
 
+FROM gcr.io/distroless/cc
 COPY --from=builder /scx/target/release/scx_rustland /scx_rustland
-COPY --from=builder /usr/lib/$COPY_LIBS_DIR/libelf.so.1 /usr/lib/libelf.so.1
-COPY --from=builder /usr/lib/$COPY_LIBS_DIR/libz.so.1 /usr/lib/libz.so.1
-COPY --from=builder /usr/lib/$COPY_LIBS_DIR/libseccomp.so.2 /usr/lib/libseccomp.so.2
+COPY --from=libs /usr/lib/libelf.so.1 /usr/lib/libelf.so.1
+COPY --from=libs /usr/lib/libz.so.1 /usr/lib/libz.so.1
+COPY --from=libs /usr/lib/libseccomp.so.2 /usr/lib/libseccomp.so.2
 
 CMD ["/scx_rustland"]