Doc: add tutorial about how to use optee-utee-build

1. add document "Writing Rust TAs using optee-utee-build"
2. suggest developers using optee-utee-build in
   "Migrating to new building env"
3. add description about the supported host machines in README.md

Signed-off-by: ivila <[email protected]>
Reviewed-by: Sumit Garg <[email protected]>
Reviewed-by: Yuan Zhuang <[email protected]>

README.md

@@ -157,6 +157,9 @@ Prerequisites](https://optee.readthedocs.io/en/latest/building/prerequisites.htm
 
 ### Setup Building Environment
 
+Currently, we support building on both `aarch64` and `x86_64` host machines, and
+ they share the same steps.
+
 1. Install the Rust environment and toolchains:
 
    ```sh

docs/README.md

@@ -8,3 +8,4 @@ permalink: /trustzone-sdk-docs
 * [Debugging OP-TEE TA](debugging-optee-ta.md)
 * [Expanding TA Secure Memory on QEMUv8](expanding-ta-secure-memory-on-qemuv8.md)
 * [Building Rust CA as Android ELF](building-rust-ca-as-android-elf.md)
+* [Writing Rust TAs using optee-utee-build](writing-rust-tas-using-optee-utee-build.md)

docs/migrating-to-new-building-env.md

@@ -2,6 +2,11 @@
 permalink: /trustzone-sdk-docs/migrating-to-new-building-env.md
 ---
 
+> After optee-utee-build release, this doc is keeping for developers 
+who intend to know the detail of building process, we suggest use 
+[optee-utee-build](./writing-rust-tas-using-optee-utee-build.md) for building 
+instead.
+
 ## Migration Guide: Moving from `master` to `main` Branch (Post-Oct 2024)
 
 Since the `main` branch (after October 2024) introduces breaking changes 

docs/writing-rust-tas-using-optee-utee-build.md

@@ -0,0 +1,243 @@
+---
+permalink: /trustzone-sdk-docs/writing-rust-tas-using-optee-utee-build.md
+---
+
+Currently we provide a `optee-utee-build` crate to simplify the compilcated
+building process of TA, and we recommend everyone use it in future developement.
+
+* For legacy app structures migrating to use this crate, refer to [Migration
+  Guide](#migration-guide)
+* If you're new to development, start with [Minimal Example](#minimal-example)
+* To customize the build process, see [Customization](#customization)
+
+# Minimal Example
+
+Assuming currently we are developing a `hello_world` TA, and we want to build it
+with `optee-utee-build` crate, we can do it by following steps.
+
+Firstly, we should add `optee-utee-build` in `build-dependencies`:
+
+```shell
+cargo add --build optee-utee-build
+```
+
+Secondly, we set a `ta_config` and call `optee-utee-build::build` with it in
+build.rs:
+
+```rust
+use proto;
+use optee_utee_build::{TaConfig, Error, RustEdition};
+
+fn main() -> Result<(), Error> {
+    let ta_config = TaConfig::new_default_with_cargo_env(proto::UUID)?;
+    optee_utee_build::build(RustEdition::Before2024, ta_config)
+}
+```
+
+It will generate a `user_ta_header.rs` file and setup all the required
+configurations of the linker of rustc.
+
+Finally, we include the generated `user_ta_header.rs` in the source codes,
+normally we put it in `src/main.rs`.
+
+```rust
+// src/main.rs
+include!(concat!(env!("OUT_DIR"), "/user_ta_header.rs"));
+```
+
+After that, everything finished, we can start building the TA now.
+
+For full codes, you can check the [`hello_world-rs example`](https://github.com/apache/incubator-teaclave-trustzone-sdk/tree/main/examples/hello_world-rs/ta)
+
+## Explaination of Minimal Example
+
+### 1. The TaConfig
+
+This is a struct that use for the configuration of the TA we are developing, it
+has some public fields:
+
+1. **uuid**: the identifier of TA.
+2. **ta_flags**: combination of some bitflags.  
+   for available values, you may check [user_ta_header.h in optee_os](https://github.com/OP-TEE/optee_os/blob/c2e42a8f03a5bb6b894ef85ae409f54760c1f50e/lib/libutee/include/user_ta_header.h#L13-L53)
+3. **ta_data_size**: the size in bytes of the TA allocation pool.
+4. **ta_stack_size**: the size in bytes of the stack used for TA execution.
+5. **ta_version**: a version string of TA, should be in semver format.
+6. **ta_description**: the desciption of TA.
+7. **trace_level**: the default trace level of TA.  
+   for available values, you may check [trace_levels.h in optee_os](https://github.com/OP-TEE/optee_os/blob/c2e42a8f03a5bb6b894ef85ae409f54760c1f50e/lib/libutils/ext/include/trace_levels.h#L26-L31)
+8. **trace_ext**: an extra prefix string when output trace log.
+9. **ta_framework_stack_size**: the size in bytes of the stack used for Trusted
+Core Framework.  
+   currently used for trace framework and invoke command, should not be less
+   than 2048.
+10. **ext_properties**: the extra custom properties.
+
+We can construct the `TaConfig` by providing all of the public fields manually,
+or use our standard constructor:
+
+1. **new_default**: construct a default TaConfig by providing uuid, ta_version 
+and ta_description, with other configurations set to suggested values, you can 
+update those configurations later.
+2. **new_default_with_cargo_env**: it's a constructor wrapped with new_default, 
+but take `version` and `description` from cargo.toml so simply providing a uuid 
+as parameter is enough.
+
+### 2. The RustEdition
+
+The generated `user_ta_header.rs` must be different between `edition of 2024`
+and `edition before 2024`, and currently there is no official stable way to know
+what edition we are compiling with, so we provide a argument to set with.
+
+> #### What’s the difference?
+> the generated `user_ta_header.rs` file include some const variables and global
+functions tagged with `no_mangle` and `link_section`, start from rust edition of
+2024, they must be wrapped with unsafe, or rustc will output a compilation error
+(while before edition of 2024 it must not, or rustc will output a syntax error).
+
+# Customization
+
+`optee-utee-build` provide some structs for flexible use.
+
+### 1. Builder
+
+Instead of calling the `build` function directly, you can use Builder for
+customization.
+
+Usage:
+
+```Rust
+use proto;
+use optee_utee_build::{TaConfig, Builder, Error, RustEdition, LinkType};
+
+fn main() -> Result<(), Error> {
+    let ta_config = TaConfig::new_default_with_cargo_env(proto::UUID)?;
+    Builder::new(RustEdition::Before2024, ta_config)
+      .out_dir("/tmp")
+      .header_file_name("my_generated_user_ta_header.rs")
+      .link_type(LinkType::CC)
+      .build()
+}
+```
+
+As you can see from the codes, there are some customizations of the builder:
+1. **out_dir**: change directory of output files.  
+   default to OUT_DIR by cargo.
+2. **header_file_name**: change name of output header file.  
+   default to `user_ta_header.rs`
+3. **link_type**: set link_type manually.  
+   there are some difference in parameters in
+   linkers between `CC` and `LD` types, for example, `--sort-section` in `CC` types
+   of linkers changes to `-Wl,--sort-section`, we will try to detect current linker
+   that cargo using, you can use this function to set it manually if you think our
+   detection mismatch.
+
+### 2. Linker
+For developers who prefer to use a hand-written `user_ta_header.rs` and only
+want `optee-utee-build` to handle the linking process, they can use the
+`Linker`, otherwise, try `Builder` instead.
+
+Usage:
+
+``` rust
+use optee_utee_build::{Linker, Error};
+use std::env;
+
+fn main() -> Result<(), Error> {
+  let out_dir = env::var("OUT_DIR")?;
+  Linker::auto().link_all(out_dir)?;
+  Ok(())
+}
+```
+
+When linking manually, developers construct a `Linker` and calling the
+`link_all` method by providing the out_dir, and linker will generate some
+required files (link script, etc, used by linker) into out_dir and handle all
+the linking stuff.
+
+In above codes, we use `auto` to construct the linker, it will detect current
+linker that cargo using automatically, you can use `new` function to construct
+the linker manually if you think our detection mismatch.
+```rust
+use optee_utee_build::{Linker, Error, LinkType};
+use std::env;
+
+fn main() -> Result<(), Error> {
+  let out_dir = env::var("OUT_DIR")?;
+  Linker::new(LinkerType::CC).link_all(out_dir)?;
+  Ok(())
+}
+```
+
+### 3. HeaderFileGenerator
+For developers who prefer to do the linking themselves and only want
+`optee-utee-build` to generate the header file, they can use the
+`HeaderFileGenerator`, otherwise, try `Builder` instead.
+
+Usage:
+
+```rust
+use optee_utee_build::{HeaderFileGenerator, TaConfig, RustEdition, Error};
+
+fn main() -> Result<(), Error> {
+  const UUID: &str = "26509cec-4a2b-4935-87ab-762d89fbf0b0";
+  let ta_config = TaConfig::new_default(UUID, "0.1.0", "example")?;
+  let codes = HeaderFileGenerator::new(RustEdition::Before2024).generate(&ta_config)?;
+  Ok(std::io::Write("/tmp/user_ta_header.rs", codes.as_bytes())?)
+}
+
+```
+
+# Migration Guide
+
+For developers still using `const configuration values` in `src/main.rs` and
+`custom build scripts` in `build.rs`(described in [\[migrating-to-new-building-env\]](https://github.com/apache/incubator-teaclave-trustzone-sdk/blob/main/docs/migrating-to-new-building-env.md)),
+they can upgrade to `optee-utee-build` by following step:
+
+Firstly, add `optee-utee-build` as `build-dependencies`:
+
+```shell
+cargo add --build optee-utee-build
+```
+
+Secondly, in `build.rs`, remove codes of `custom build scripts`, and use
+`optee_utee_build::build` instead:
+
+```rust
+// ... other imports
+use optee_utee_build::{TaConfig, Error}
+
+fn main() -> Result<(), Error> {
+  // should customize the ta_config with the same as const configuration values
+  // in your src/main.rs
+  let ta_config = TaConfig::new_default_with_cargo_env(proto::UUID)?
+    .ta_stack_size(10 * 1024); 
+  optee_utee_build::build(RustEdition::Before2024, ta_config)?;
+
+  // ... other build scripts
+}
+```
+
+Thirdly, remove `const configuration values` in `src/main.rs`, keep the line of
+`include user_ta_header.rs`.
+
+```rust
+/// ... other codes in src/main.rs
+
+/* remove const configuration values, move them to TaConfig in src/main.rs
+// TA configurations
+const TA_FLAGS: u32 = 0;
+const TA_DATA_SIZE: u32 = 32 * 1024;
+const TA_STACK_SIZE: u32 = 2 * 1024;
+const TA_VERSION: &[u8] = b"0.1\0";
+const TA_DESCRIPTION: &[u8] = b"This is a hello world example.\0";
+const EXT_PROP_VALUE_1: &[u8] = b"Hello World TA\0";
+const EXT_PROP_VALUE_2: u32 = 0x0010;
+const TRACE_LEVEL: i32 = 4;
+const TRACE_EXT_PREFIX: &[u8] = b"TA\0";
+const TA_FRAMEWORK_STACK_SIZE: u32 = 2048;
+*/
+
+include!(concat!(env!("OUT_DIR"), "/user_ta_header.rs"));  // keep this line
+```
+
+Finally, delete the useless `ta_static.rs` and start building now.