feat: Add kraftld

This implements a `kraftld` linker shim acting as a gcc-style linker.

It accepts the same arguments and forwards them to `UK_LDFLAGS`.
It removes flags that are known to be incompatible.
Furthermore, it sanitizes relative paths for the Unikraft build system.

`kraftld` also extracts any file dependencies for `UK_LDEPS`.
Lastly, it parses `-o <OUTPUT>` and copies the KraftKit output image.
Currently, it assumes the `default_qemu-x86_64`.
Future versions of KraftKit will support an output option.
`kraftld` will then adapt that option instead.

`kraftld` is currently targeting the Rust compiler.
Other compilers may or may not work as well.

Signed-off-by: Martin Kröning <[email protected]>
GitHub-Closes: unikraft#612

scripts/kraftld

@@ -0,0 +1,106 @@
+#!/usr/bin/env bash
+
+# The KraftKit linker (`kraftld`).
+#
+# This linker transparently encapsulates KraftKit and the Unikraft build system
+# to include the provided object files in a Unikraft build.
+# It is a drop-in replacement for the GNU linker (`ld`).
+#
+# A `Kraftfile` is required to configure the build process.
+# If only one unnamed target configuration exists, this works out of the box.
+# If the `Kraftfile` contains multiple targets, the current target has to be
+# specified via environment variables:
+# - `KRAFTKIT_TARGET` corresponds to `kraft build --target $KRAFTKIT_TARGET`
+# - `KRAFTKIT_ARCH` corresponds to `kraft build --arch $KRAFTKIT_ARCH`
+# - `KRAFTKIT_PLAT` corresponds to `kraft build --plat $KRAFTKIT_PLAT`
+
+
+# Bash strict mode
+set -euo pipefail
+IFS=$'\n\t'
+
+
+# Prepare `UK_LDFLAGS`
+LDFLAGS="$*"
+
+# Make all relative object paths absolute for make
+# rel_path.o -> $PWD/rel_path.o
+LDFLAGS=$(echo "$LDFLAGS" | sed -Ee 's,(^[^/].*\.o),'"$PWD"'\/\1,g' )
+
+# Remove -nodefaultlibs
+LDFLAGS=${LDFLAGS/-nodefaultlibs/}
+
+export UK_LDFLAGS="$LDFLAGS"
+
+
+# Extract `OUTPUT` and `FILES` from arguments
+FILES=""
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        -o)
+            # Extract output path
+            OUTPUT="$2"
+            shift
+            shift
+            ;;
+        -L)
+            # Ignore other options with arguments
+            shift
+            shift
+            ;;
+        -*)
+            # Ignore other options without arguments
+            shift
+            ;;
+        *)
+            # Collect input files for `UK_LDEPS`
+            # This creates a leading whitespace but that's okay
+            FILES+=" $1"
+            shift
+            ;;
+    esac
+done
+
+export UK_LDEPS="$FILES"
+
+
+# Parse target selection environment variables
+if [[ -z "${KRAFTKIT_TARGET:-}" ]]; then
+    KRAFTKIT_ARG_TARG=()
+    KRAFTKIT_TARGET=workspace
+else
+    KRAFTKIT_ARG_TARG=("--target=$KRAFTKIT_TARGET")
+fi
+if [[ -z "${KRAFTKIT_ARCH:-}" ]]; then
+    KRAFTKIT_ARCH='*'
+    KRAFTKIT_ARG_ARCH=()
+else
+    KRAFTKIT_ARG_ARCH=("--arch=$KRAFTKIT_ARCH")
+fi
+if [[ -z "${KRAFTKIT_PLAT:-}" ]]; then
+    KRAFTKIT_PLAT='*'
+    KRAFTKIT_ARG_PLAT=()
+else
+    KRAFTKIT_ARG_PLAT=("--plat=$KRAFTKIT_PLAT")
+fi
+
+
+# Finally, build the Unikraft image
+kraft build --log-level debug --log-type basic --no-cache "${KRAFTKIT_ARG_TARG[@]}" "${KRAFTKIT_ARG_PLAT[@]}" "${KRAFTKIT_ARG_ARCH[@]}"
+
+
+# Find KraftKit output image
+# Don't match any files with extensions
+mapfile -t kraft_output < <(find .unikraft/build -maxdepth 1 -type f ! -name "*.*" -name "${KRAFTKIT_TARGET}_${KRAFTKIT_PLAT}-${KRAFTKIT_ARCH}")
+
+if [[ "${#kraft_output[@]}" -ne 1 ]]; then
+    echo "Cannot decide on kraft output file"
+    echo "Specify \$KRAFTKIT_TARGET, \$KRAFTKIT_ARCH, or \$KRAFTKIT_PLAT"
+    exit 1
+fi
+
+kraft_output="${kraft_output[0]}"
+
+
+# Copy KraftKit output to linker output
+cp "$kraft_output" "$OUTPUT"