Add custom target, switch to cargo xbuild, add README

Author: geofft

README.md

@@ -1 +1,34 @@
-# linux-kernel-module-rust
+# Linux kernel modules in safe Rust
+
+1. Install [cargo-xbuild](https://github.com/rust-osdev/cargo-xbuild):
+
+```
+cargo install cargo-xbuild
+```
+
+2. cd to one of the examples
+
+```
+cd hello-world
+```
+
+3. Build the static object with cargo xbuild, pointing it at our custom target
+
+```
+RUST_TARGET_PATH=~/linux-kernel-module-rust cargo xbuild --target x86_64-linux-kernel-module
+
+```
+
+4. Build the kernel module using the Linux kernel build system (kbuild)
+
+```
+make
+```
+
+5. Load and unload the module!
+
+```
+sudo insmod helloworld.ko
+sudo rmmod helloworld
+dmesg | tail
+```

hello-world/Cargo.toml

@@ -8,7 +8,3 @@ crate-type = ["staticlib"]
 
 [dependencies]
 linux-kernel-module = { path = ".." }
-
-[profile.dev]
-# TODO: can be removed once we have a custom target.json
-panic = "abort"

hello-world/Makefile

@@ -1,5 +1,5 @@
 obj-m := helloworld.o
-helloworld-objs := target/debug/libhello_world.a ../src/printk_helper.o
+helloworld-objs := target/x86_64-linux-kernel-module/debug/libhello_world.a ../src/printk_helper.o
 EXTRA_LDFLAGS += --gc-sections --entry=init_module --undefined=cleanup_module
 
 all:

src/lib.rs

@@ -68,11 +68,5 @@ extern "C" fn panic_fmt() -> ! {
     loop {}
 }
 
-// TODO: we expect this to go away once we have a target.json and we rebuild libcore.
-#[no_mangle]
-pub extern "C" fn _Unwind_Resume() -> ! {
-    loop {}
-}
-
 #[global_allocator]
 static ALLOCATOR: allocator::KernelAllocator = allocator::KernelAllocator;

static-filesystem/Cargo.toml

@@ -8,7 +8,3 @@ crate-type = ["staticlib"]
 
 [dependencies]
 linux-kernel-module = { path = ".." }
-
-[profile.dev]
-# TODO: can be removed once we have a custom target.json
-panic = "abort"

x86_64-linux-kernel-module.json

@@ -0,0 +1,32 @@
+{
+  "arch": "x86_64",
+  "cpu": "x86-64",
+  "code-model": "kernel",
+  "data-layout": "e-m:e-i64:64-f80:128-n8:16:32:64-S128",
+  "disable-redzone": true,
+  "eliminate-frame-pointer": false,
+  "env": "gnu",
+  "features": "-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-3dnow,-3dnowa,-avx,-avx2,+soft-float",
+  "linker-flavor": "gcc",
+  "linker-is-gnu": true,
+  "llvm-target": "x86_64-unknown-linux-gnu",
+  "max-atomic-width": 64,
+  "no-compiler-rt": true,
+  "os": "none",
+  "panic-strategy": "abort",
+  "position-independent-executables": true,
+  "pre-link-args": {
+    "gcc": [
+      "-Wl,--as-needed",
+      "-Wl,-z,noexecstack",
+      "-m64"
+    ]
+  },
+  "relocation-model": "static",
+  "relro-level": "full",
+  "target-c-int-width": "32",
+  "target-endian": "little",
+  "target-family": "unix",
+  "target-pointer-width": "64",
+  "vendor": "unknown"
+}