build: Allow building without mstpm

Remove the default dependency from "kernel" on mstpm so it can be
compiled without it. Change the Makefile to specify mstpm as feature by
default. This allows running FEATURES='""' make to not build the mstpm.

To run unit tests without testing mstpm, use:

FEATURES_TEST='""' SVSM_ARGS_TEST='--exclude libmstpm' make test

Signed-off-by: Adam Dunlap <[email protected]>

Makefile

@@ -1,10 +1,8 @@
-FEATURES ?= "default"
-SVSM_ARGS = --features ${FEATURES}
+FEATURES ?= mstpm
+SVSM_ARGS += --features ${FEATURES}
 
-SVSM_ARGS_TEST = --no-default-features
-ifdef FEATURES_TEST
-	SVSM_ARGS_TEST += --features ${FEATURES_TEST}
-endif
+FEATURES_TEST ?= mstpm
+SVSM_ARGS_TEST += --no-default-features --features ${FEATURES_TEST}
 
 ifdef RELEASE
 TARGET_PATH=release
@@ -112,15 +110,15 @@ bin/meta.bin: utils/gen_meta utils/print-meta bin
 	./utils/gen_meta $@
 
 bin/stage2.bin: bin
-	cargo build --manifest-path kernel/Cargo.toml ${CARGO_ARGS} --no-default-features --bin stage2
+	cargo build --manifest-path kernel/Cargo.toml ${CARGO_ARGS} --bin stage2
 	objcopy -O binary ${STAGE2_ELF} $@
 
 bin/svsm-kernel.elf: bin
 	cargo build ${CARGO_ARGS} ${SVSM_ARGS} --bin svsm
 	objcopy -O elf64-x86-64 --strip-unneeded ${SVSM_KERNEL_ELF} $@
 
 bin/test-kernel.elf: bin
-	LINK_TEST=1 cargo +nightly test ${CARGO_ARGS} -p svsm --config 'target.x86_64-unknown-none.runner=["sh", "-c", "cp $$0 ../${TEST_KERNEL_ELF}"]'
+	LINK_TEST=1 cargo +nightly test ${CARGO_ARGS} ${SVSM_ARGS_TEST} -p svsm --config 'target.x86_64-unknown-none.runner=["sh", "-c", "cp $$0 ../${TEST_KERNEL_ELF}"]'
 	objcopy -O elf64-x86-64 --strip-unneeded ${TEST_KERNEL_ELF} bin/test-kernel.elf
 
 ${FS_BIN}: bin

kernel/Cargo.toml

@@ -38,7 +38,7 @@ libmstpm = { workspace = true, optional = true }
 test.workspace = true
 
 [features]
-default = ["mstpm"]
+default = []
 enable-gdb = ["dep:gdbstub", "dep:gdbstub_arch"]
 mstpm = ["dep:libmstpm"]