Fix to be able to use a target specification JSON file and document the process

Author: antoyo

Readme.md

@@ -322,7 +322,12 @@ generate it in [gimple.md](./doc/gimple.md).
  * Set the path to the cross-compiling libgccjit in `gcc_path`.
  * Make sure you have the linker for your target (for instance `m68k-unknown-linux-gnu-gcc`) in your `$PATH`. Currently, the linker name is hardcoded as being `$TARGET-gcc`. Specify the target when building the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu`.
  * Build your project by specifying the target: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../cargo.sh build --target m68k-unknown-linux-gnu`.
- * If the target is not yet supported by the Rust compiler, create a [target specification file](https://docs.rust-embedded.org/embedonomicon/custom-target.html) (note that the `arch` specified in this file must be supported by the rust compiler).
+
+If the target is not yet supported by the Rust compiler, create a [target specification file](https://docs.rust-embedded.org/embedonomicon/custom-target.html) (note that the `arch` specified in this file must be supported by the rust compiler).
+Then, you can use it the following way:
+
+ * Add the target specification file using `--target` as an **absolute** path to build the sysroot: `./y.sh build --target-triple m68k-unknown-linux-gnu --target $(pwd)/m68k-unknown-linux-gnu.json`
+ * Build your project by specifying the target specification file: `OVERWRITE_TARGET_TRIPLE=m68k-unknown-linux-gnu ../cargo.sh build --target path/to/m68k-unknown-linux-gnu.json`.
 
 If you get the following error:
 

build_system/src/build.rs

@@ -1,4 +1,4 @@
-use crate::config::set_config;
+use crate::config::{set_config, ConfigInfo};
 use crate::utils::{
     get_gcc_path, run_command, run_command_with_output_and_env, walk_dir,
 };
@@ -55,6 +55,15 @@ impl BuildArg {
                         );
                     }
                 }
+                "--target" => {
+                    if args.next().is_some() {
+                        // Handled in config.rs.
+                    } else {
+                        return Err(
+                            "Expected a value after `--target`, found nothing".to_string()
+                        );
+                    }
+                }
                 arg => return Err(format!("Unknown argument `{}`", arg)),
             }
         }
@@ -80,7 +89,7 @@ impl BuildArg {
 fn build_sysroot(
     env: &mut HashMap<String, String>,
     release_mode: bool,
-    target_triple: &str,
+    config: &ConfigInfo,
 ) -> Result<(), String> {
     std::env::set_current_dir("build_sysroot")
         .map_err(|error| format!("Failed to go to `build_sysroot` directory: {:?}", error))?;
@@ -143,7 +152,7 @@ fn build_sysroot(
                 &"cargo",
                 &"build",
                 &"--target",
-                &target_triple,
+                &config.target,
                 &"--release",
             ],
             None,
@@ -156,7 +165,7 @@ fn build_sysroot(
                 &"cargo",
                 &"build",
                 &"--target",
-                &target_triple,
+                &config.target,
             ],
             None,
             Some(env),
@@ -165,14 +174,14 @@ fn build_sysroot(
     };
 
     // Copy files to sysroot
-    let sysroot_path = format!("sysroot/lib/rustlib/{}/lib/", target_triple);
+    let sysroot_path = format!("sysroot/lib/rustlib/{}/lib/", config.target_triple);
     fs::create_dir_all(&sysroot_path)
         .map_err(|error| format!("Failed to create directory `{}`: {:?}", sysroot_path, error))?;
     let copier = |dir_to_copy: &Path| {
         run_command(&[&"cp", &"-r", &dir_to_copy, &sysroot_path], None).map(|_| ())
     };
     walk_dir(
-        &format!("target/{}/{}/deps", target_triple, channel),
+        &format!("target/{}/{}/deps", config.target_triple, channel),
         copier,
         copier,
     )?;
@@ -216,7 +225,7 @@ fn build_codegen(args: &BuildArg) -> Result<(), String> {
     build_sysroot(
         &mut env,
         args.sysroot_release_channel,
-        &config.target_triple,
+        &config,
     )?;
     Ok(())
 }

build_system/src/config.rs

@@ -3,6 +3,7 @@ use std::collections::HashMap;
 use std::env as std_env;
 
 pub struct ConfigInfo {
+    pub target: String,
     pub target_triple: String,
     pub rustc_command: Vec<String>,
 }
@@ -30,25 +31,43 @@ pub fn set_config(
     let host_triple = get_rustc_host_triple()?;
     let mut linker = None;
     let mut target_triple = host_triple.clone();
+    let mut target = target_triple.clone();
 
     // We skip binary name and the command.
     let mut args = std::env::args().skip(2);
 
+    let mut set_target_triple = false;
+    let mut set_target = false;
     while let Some(arg) = args.next() {
         match arg.as_str() {
             "--target-triple" => {
                 if let Some(arg) = args.next() {
                     target_triple = arg;
+                    set_target_triple = true;
                 } else {
                     return Err(
                         "Expected a value after `--target-triple`, found nothing".to_string()
                     );
                 }
             },
+            "--target" => {
+                if let Some(arg) = args.next() {
+                    target = arg;
+                    set_target = true;
+                } else {
+                    return Err(
+                        "Expected a value after `--target`, found nothing".to_string()
+                    );
+                }
+            },
             _ => (),
         }
     }
 
+    if set_target_triple && !set_target {
+        target = target_triple.clone();
+    }
+
     if host_triple != target_triple {
         linker = Some(format!("-Clinker={}-gcc", target_triple));
     }
@@ -123,7 +142,8 @@ pub fn set_config(
         "target/out".to_string(),
     ]);
     Ok(ConfigInfo {
-        target_triple: target_triple.to_string(),
+        target,
+        target_triple,
         rustc_command,
     })
 }