Build some C in Cargo project

Makefile

@@ -63,6 +63,8 @@ CFLAGS += -MD
 CFLAGS += -mcmodel=medany
 CFLAGS += -ffreestanding -fno-common -nostdlib -mno-relax
 CFLAGS += -I.
+CFLAGS += -march=rv64gc
+CFLAGS += -mabi=lp64d
 CFLAGS += $(shell $(CC) -fno-stack-protector -E -x c /dev/null >/dev/null 2>&1 && echo -fno-stack-protector)
 TARGET_TRIPLE = riscv64gc-unknown-none-elf
 
@@ -77,7 +79,7 @@ endif
 LDFLAGS = -z max-page-size=4096
 
 $K/kernel: $(OBJS) $K/kernel.ld $U/initcode $R/src
-	cargo +nightly -Z unstable-options -C $R build
+	CC="$(CC)" CFLAGS="$(CFLAGS)" cargo +nightly -Z unstable-options -C $R build
 	$(LD) $(LDFLAGS) -T $K/kernel.ld -o $K/kernel $(OBJS) $R/target/$(TARGET_TRIPLE)/debug/librustkernel.a
 	$(OBJDUMP) -S $K/kernel > $K/kernel.asm
 	$(OBJDUMP) -t $K/kernel | sed '1,/SYMBOL TABLE/d; s/ .* / /; /^$$/d' > $K/kernel.sym

kernel/rustkernel/.cargo/config.toml

@@ -1,3 +1,3 @@
 [build]
 target = "riscv64gc-unknown-none-elf"
-rustflags = ["-Csoft-float=n"]
+rustflags = ["-C", "soft-float=n"]

kernel/rustkernel/Cargo.lock

@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "cc"
+version = "1.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2aba8f4e9906c7ce3c73463f62a7f0c65183ada1a2d47e397cc8810827f9694f"
+
 [[package]]
 name = "rustkernel"
 version = "0.1.0"
+dependencies = [
+ "cc",
+]

kernel/rustkernel/Cargo.toml

@@ -5,5 +5,8 @@ edition = "2021"
 
 [dependencies]
 
+[build-dependencies]
+cc = "1.0"
+
 [lib]
 crate-type = ["staticlib"]

kernel/rustkernel/build.rs

@@ -0,0 +1,45 @@
+fn main() {
+    cc::Build::new()
+        .compiler("riscv64-unknown-elf-gcc")
+        .flag("-Wall")
+        .flag("-Werror")
+        .flag("-O")
+        .flag("-fno-omit-frame-pointer")
+        .flag("-ggdb")
+        .flag("-gdwarf-2")
+        .flag("-MD")
+        .flag("-mcmodel=medany")
+        .flag("-ffreestanding")
+        .flag("-fno-common")
+        .flag("-nostdlib")
+        .flag("-mno-relax")
+        .flag("-I.")
+        .flag("-march=rv64gc")
+        .flag("-mabi=lp64d")
+        .flag_if_supported("-fno-stack-protector")
+        .flag_if_supported("-fno-pie")
+        .flag_if_supported("-no-pie")
+        .file("src/c/layered.c")
+        .compile("layered");
+}
+
+/*
+Wall -Werror -O -fno-omit-frame-pointer -ggdb -gdwarf-2
+-MD
+-mcmodel=medany
+-ffreestanding -fno-common -nostdlib -mno-relax
+-I.
+
+
+-fno-stack-protector
+-fno-pie -no-pie
+
+TARGET_TRIPLE = riscv64gc-unknown-none-elf
+
+# Disable PIE when possible (for Ubuntu 16.10 toolchain)
+ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]no-pie'),)
+endif
+ifneq ($(shell $(CC) -dumpspecs 2>/dev/null | grep -e '[^f]nopie'),)
+CFLAGS += -fno-pie -nopie
+endif
+*/

kernel/rustkernel/src/c/layered.c

@@ -0,0 +1,3 @@
+char *test_layered() {
+  return "Hello from layered C!";
+}

kernel/rustkernel/src/lib.rs

@@ -6,6 +6,7 @@ use core::ffi::{c_char, CStr};
 extern "C" {
     pub fn print(message: *const c_char);
     fn panic(panic_message: *const c_char) -> !;
+    fn test_layered() -> *const c_char;
 }
 
 #[no_mangle]
@@ -16,6 +17,7 @@ pub extern "C" fn rust_main() {
                 .unwrap()
                 .as_ptr(),
         );
+        print(test_layered());
     }
 }