Merge pull request #427 from GuillaumeGomez/config-file

Switch to `config.toml` instead of `gcc-path`

18 files changed, 227 insertions, 90 deletions

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 426eabdd176..ba64f40acc4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -55,13 +55,13 @@ jobs:
     - name: Setup path to libgccjit
       run: |
           sudo dpkg --force-overwrite -i gcc-13.deb
-          echo /usr/lib/ > gcc_path
+          echo 'gcc-path = "/usr/lib/"' > config.toml
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
+        echo "LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
 
     #- name: Cache rust repository
       ## We only clone the rust repository for rustc tests
diff --git a/.github/workflows/failures.yml b/.github/workflows/failures.yml
index 7aaf47facd8..ae00a257e24 100644
--- a/.github/workflows/failures.yml
+++ b/.github/workflows/failures.yml
@@ -52,7 +52,10 @@ jobs:
 
     - name: Setup path to libgccjit
       if: matrix.libgccjit_version.gcc == 'libgccjit12.so'
-      run: echo /usr/lib/gcc/x86_64-linux-gnu/12 > gcc_path
+      run: |
+          echo 'gcc-path = "/usr/lib/gcc/x86_64-linux-gnu/12"' > config.toml
+          echo "LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12" >> $GITHUB_ENV
+          echo "LD_LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12" >> $GITHUB_ENV
 
     - name: Download artifact
       if: matrix.libgccjit_version.gcc != 'libgccjit12.so'
@@ -62,12 +65,12 @@ jobs:
       if: matrix.libgccjit_version.gcc != 'libgccjit12.so'
       run: |
           sudo dpkg --force-overwrite -i gcc-13.deb
-          echo /usr/lib/ > gcc_path
+          echo 'gcc-path = "/usr/lib"' > config.toml
+          echo "LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
+          echo "LD_LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
 
     #- name: Cache rust repository
diff --git a/.github/workflows/gcc12.yml b/.github/workflows/gcc12.yml
index 8d4f88ea7b1..f7bb1560492 100644
--- a/.github/workflows/gcc12.yml
+++ b/.github/workflows/gcc12.yml
@@ -47,13 +47,13 @@ jobs:
       run: sudo apt-get install ninja-build ripgrep llvm-14-tools libgccjit-12-dev
 
     - name: Setup path to libgccjit
-      run: echo /usr/lib/gcc/x86_64-linux-gnu/12 > gcc_path
+      run: echo 'gcc-path = "/usr/lib/gcc/x86_64-linux-gnu/12"' > config.toml
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
+        echo "LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12" >> $GITHUB_ENV
 
     #- name: Cache rust repository
       ## We only clone the rust repository for rustc tests
diff --git a/.github/workflows/m68k.yml b/.github/workflows/m68k.yml
index b0866bafb8e..2428125483b 100644
--- a/.github/workflows/m68k.yml
+++ b/.github/workflows/m68k.yml
@@ -65,13 +65,13 @@ jobs:
     - name: Setup path to libgccjit
       run: |
           sudo dpkg -i gcc-m68k-13.deb
-          echo /usr/lib/ > gcc_path
+          echo 'gcc-path = "/usr/lib/"' > config.toml
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
+        echo "LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
 
     #- name: Cache rust repository
       ## We only clone the rust repository for rustc tests
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 7628fd65571..729a76e80bf 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -42,13 +42,13 @@ jobs:
     - name: Setup path to libgccjit
       run: |
           sudo dpkg --force-overwrite -i gcc-13.deb
-          echo /usr/lib/ > gcc_path
+          echo 'gcc-path = "/usr/lib/"' > config.toml
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
+        echo "LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
 
     - name: Build
       run: |
diff --git a/.github/workflows/stdarch.yml b/.github/workflows/stdarch.yml
index a5c3a5456bd..65687756cd4 100644
--- a/.github/workflows/stdarch.yml
+++ b/.github/workflows/stdarch.yml
@@ -56,13 +56,13 @@ jobs:
     - name: Setup path to libgccjit
       run: |
           sudo dpkg --force-overwrite -i gcc-13.deb
-          echo /usr/lib/ > gcc_path
+          echo 'gcc-path = "/usr/lib/"' > config.toml
 
     - name: Set env
       run: |
-        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
-        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
         echo "workspace="$GITHUB_WORKSPACE >> $GITHUB_ENV
+        echo "LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=/usr/lib" >> $GITHUB_ENV
 
     - name: Build
       run: |
diff --git a/.gitignore b/.gitignore
index c865386dad3..687c3a6797a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,3 +28,4 @@ tools/llvmint-2
 # The `llvm` folder is generated by the `tools/generate_intrinsics.py` script to update intrinsics.
 llvm
 build_system/target
+config.toml
diff --git a/Cargo.lock b/Cargo.lock
index 26dc7c535f8..a19de10d0d2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -24,6 +24,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4682ae6287fcf752ecaabbfcc7b6f9b72aa33933dc23a554d853aea8eea8635"
 
 [[package]]
+name = "boml"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85fdb93f04c73bff54305fa437ffea5449c41edcaadfe882f35836206b166ac5"
+
+[[package]]
 name = "cc"
 version = "1.0.79"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -185,6 +191,7 @@ checksum = "436b050e76ed2903236f032a59761c1eb99e1b0aead2c257922771dab1fc8c78"
 name = "rustc_codegen_gcc"
 version = "0.1.0"
 dependencies = [
+ "boml",
  "gccjit",
  "lang_tester",
  "object",
diff --git a/Cargo.toml b/Cargo.toml
index b0b3aeecdbd..a280ac73de0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -37,6 +37,7 @@ tempfile = "3.7.1"
 [dev-dependencies]
 lang_tester = "0.3.9"
 tempfile = "3.1.0"
+boml = "0.3.1"
 
 [profile.dev]
 # By compiling dependencies with optimizations, performing tests gets much faster.
diff --git a/Readme.md b/Readme.md
index 39ff41acf84..a380d0d5be6 100644
--- a/Readme.md
+++ b/Readme.md
@@ -49,17 +49,27 @@ $ make check-jit
 $ make check-jit RUNTESTFLAGS="-v -v -v jit.exp=jit.dg/test-asm.cc"
 ```
 
-**Put the path to your custom build of libgccjit in the file `gcc_path`.**
+**Put the path to your custom build of libgccjit in the file `config.toml`.**
+
+If you followed the instructions exactly as written (ie, you have created a `gcc-build` folder
+where gcc is built), the only thing you need to do is:
+
+```bash
+$ cp config.example.toml config.toml
+```
+
+But if you did something different, you also need to set the `gcc-path` value in `config.toml` with
+the result of this command:
 
 ```bash
-$ dirname $(readlink -f `find . -name libgccjit.so`) > gcc_path
+$ dirname $(readlink -f `find . -name libgccjit.so`)
 ```
 
 Then you can run commands like this:
 
 ```bash
 $ ./y.sh prepare # download and patch sysroot src and install hyperfine for benchmarking
-$ LIBRARY_PATH=$(cat gcc_path) LD_LIBRARY_PATH=$(cat gcc_path) ./y.sh build --release --features master
+$ ./y.sh build --release --features master
 ```
 
 To run the tests:
@@ -100,7 +110,7 @@ error: failed to copy bitcode to object file: No such file or directory (os erro
 > You should prefer using the Cargo method.
 
 ```bash
-$ LIBRARY_PATH=$(cat gcc_path) LD_LIBRARY_PATH=$(cat gcc_path) rustc +$(cat $CG_GCCJIT_DIR/rust-toolchain | grep 'channel' | cut -d '=' -f 2 | sed 's/"//g' | sed 's/ //g') -Cpanic=abort -Zcodegen-backend=$CG_GCCJIT_DIR/target/release/librustc_codegen_gcc.so --sysroot $CG_GCCJIT_DIR/build_sysroot/sysroot my_crate.rs
+$ LIBRARY_PATH="[gcc-path value]" LD_LIBRARY_PATH="[gcc-path value]" rustc +$(cat $CG_GCCJIT_DIR/rust-toolchain | grep 'channel' | cut -d '=' -f 2 | sed 's/"//g' | sed 's/ //g') -Cpanic=abort -Zcodegen-backend=$CG_GCCJIT_DIR/target/release/librustc_codegen_gcc.so --sysroot $CG_GCCJIT_DIR/build_sysroot/sysroot my_crate.rs
 ```
 
 ## Env vars
@@ -322,7 +332,7 @@ generate it in [gimple.md](./doc/gimple.md).
 #### Configuring rustc_codegen_gcc
 
  * Run `./y.sh prepare --cross` so that the sysroot is patched for the cross-compiling case.
- * Set the path to the cross-compiling libgccjit in `gcc_path`.
+ * Set the path to the cross-compiling libgccjit in `gcc-path` (in `config.toml`).
  * 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 ../y.sh cargo build --target m68k-unknown-linux-gnu`.
 
@@ -338,4 +348,4 @@ If you get the following error:
 /usr/bin/ld: unrecognised emulation mode: m68kelf
 ```
 
-Make sure you set `gcc_path` to the install directory.
+Make sure you set `gcc-path` (in `config.toml`) to the install directory.
diff --git a/build_system/Cargo.lock b/build_system/Cargo.lock
index 86268e19160..e727561a2bf 100644
--- a/build_system/Cargo.lock
+++ b/build_system/Cargo.lock
@@ -3,5 +3,14 @@
 version = 3
 
 [[package]]
+name = "boml"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85fdb93f04c73bff54305fa437ffea5449c41edcaadfe882f35836206b166ac5"
+
+[[package]]
 name = "y"
 version = "0.1.0"
+dependencies = [
+ "boml",
+]
diff --git a/build_system/Cargo.toml b/build_system/Cargo.toml
index f36709ea036..d2600ed5a03 100644
--- a/build_system/Cargo.toml
+++ b/build_system/Cargo.toml
@@ -3,6 +3,9 @@ name = "y"
 version = "0.1.0"
 edition = "2021"
 
+[dependencies]
+boml = "0.3.1"
+
 [[bin]]
 name = "y"
 path = "src/main.rs"
diff --git a/build_system/src/build.rs b/build_system/src/build.rs
index 3149560b458..efae5a46b04 100644
--- a/build_system/src/build.rs
+++ b/build_system/src/build.rs
@@ -1,5 +1,5 @@
 use crate::config::{Channel, ConfigInfo};
-use crate::utils::{get_gcc_path, run_command, run_command_with_output_and_env, walk_dir};
+use crate::utils::{run_command, run_command_with_output_and_env, walk_dir};
 use std::collections::HashMap;
 use std::ffi::OsStr;
 use std::fs;
@@ -8,17 +8,12 @@ use std::path::Path;
 #[derive(Default)]
 struct BuildArg {
     flags: Vec<String>,
-    gcc_path: String,
     config_info: ConfigInfo,
 }
 
 impl BuildArg {
     fn new() -> Result<Option<Self>, String> {
-        let gcc_path = get_gcc_path()?;
-        let mut build_arg = Self {
-            gcc_path,
-            ..Default::default()
-        };
+        let mut build_arg = Self::default();
         // We skip binary name and the `build` command.
         let mut args = std::env::args().skip(2);
 
@@ -169,7 +164,8 @@ pub fn build_sysroot(env: &HashMap<String, String>, config: &ConfigInfo) -> Resu
     fs::create_dir_all(&sysroot_src_path).map_err(|error| {
         format!(
             "Failed to create directory `{}`: {:?}",
-            sysroot_src_path.display(), error
+            sysroot_src_path.display(),
+            error
         )
     })?;
     run_command(
@@ -188,8 +184,14 @@ pub fn build_sysroot(env: &HashMap<String, String>, config: &ConfigInfo) -> Resu
 fn build_codegen(args: &mut BuildArg) -> Result<(), String> {
     let mut env = HashMap::new();
 
-    env.insert("LD_LIBRARY_PATH".to_string(), args.gcc_path.clone());
-    env.insert("LIBRARY_PATH".to_string(), args.gcc_path.clone());
+    env.insert(
+        "LD_LIBRARY_PATH".to_string(),
+        args.config_info.gcc_path.clone(),
+    );
+    env.insert(
+        "LIBRARY_PATH".to_string(),
+        args.config_info.gcc_path.clone(),
+    );
 
     let mut command: Vec<&dyn AsRef<OsStr>> = vec![&"cargo", &"rustc"];
     if args.config_info.channel == Channel::Release {
@@ -205,7 +207,7 @@ fn build_codegen(args: &mut BuildArg) -> Result<(), String> {
     }
     run_command_with_output_and_env(&command, None, Some(&env))?;
 
-    args.config_info.setup(&mut env, Some(&args.gcc_path))?;
+    args.config_info.setup(&mut env, None)?;
 
     // We voluntarily ignore the error.
     let _ = fs::remove_dir_all("target/out");
@@ -227,6 +229,7 @@ pub fn run() -> Result<(), String> {
         Some(args) => args,
         None => return Ok(()),
     };
+    args.config_info.setup_gcc_path(None)?;
     build_codegen(&mut args)?;
     Ok(())
 }
diff --git a/build_system/src/config.rs b/build_system/src/config.rs
index 1824bdd292f..5ba6233617e 100644
--- a/build_system/src/config.rs
+++ b/build_system/src/config.rs
@@ -1,7 +1,11 @@
-use crate::utils::{get_gcc_path, get_os_name, rustc_version_info, split_args};
+use crate::utils::{get_os_name, rustc_version_info, split_args};
 use std::collections::HashMap;
 use std::env as std_env;
 use std::ffi::OsStr;
+use std::fs;
+use std::path::Path;
+
+use boml::{types::TomlValue, Toml};
 
 #[derive(Default, PartialEq, Eq, Clone, Copy, Debug)]
 pub enum Channel {
@@ -19,6 +23,71 @@ impl Channel {
     }
 }
 
+fn failed_config_parsing(config_file: &str, err: &str) -> Result<ConfigFile, String> {
+    Err(format!("Failed to parse `{}`: {}", config_file, err))
+}
+
+#[derive(Default)]
+pub struct ConfigFile {
+    gcc_path: Option<String>,
+    download_gccjit: Option<bool>,
+}
+
+impl ConfigFile {
+    pub fn new(config_file: Option<&str>) -> Result<Self, String> {
+        let config_file = config_file.unwrap_or("config.toml");
+        let content = fs::read_to_string(config_file).map_err(|_| {
+            format!(
+                "Failed to read `{}`. Take a look at `Readme.md` to see how to set up the project",
+                config_file,
+            )
+        })?;
+        let toml = Toml::parse(&content).map_err(|err| {
+            format!(
+                "Error occurred around `{}`: {:?}",
+                &content[err.start..=err.end],
+                err.kind
+            )
+        })?;
+        let mut config = Self::default();
+        for (key, value) in toml.iter() {
+            match (key, value) {
+                ("gcc-path", TomlValue::String(value)) => {
+                    config.gcc_path = Some(value.as_str().to_string())
+                }
+                ("gcc-path", _) => {
+                    return failed_config_parsing(config_file, "Expected a string for `gcc-path`")
+                }
+                ("download-gccjit", TomlValue::Boolean(value)) => {
+                    config.download_gccjit = Some(*value)
+                }
+                ("download-gccjit", _) => {
+                    return failed_config_parsing(
+                        config_file,
+                        "Expected a boolean for `download-gccjit`",
+                    )
+                }
+                _ => return failed_config_parsing(config_file, &format!("Unknown key `{}`", key)),
+            }
+        }
+        if config.gcc_path.is_none() && config.download_gccjit.is_none() {
+            return failed_config_parsing(
+                config_file,
+                "At least one of `gcc-path` or `download-gccjit` value must be set",
+            );
+        }
+        if let Some(gcc_path) = config.gcc_path.as_mut() {
+            let path = Path::new(gcc_path);
+            *gcc_path = path
+                .canonicalize()
+                .map_err(|err| format!("Failed to get absolute path of `{}`: {:?}", gcc_path, err))?
+                .display()
+                .to_string();
+        }
+        Ok(config)
+    }
+}
+
 #[derive(Default, Debug)]
 pub struct ConfigInfo {
     pub target: String,
@@ -33,6 +102,8 @@ pub struct ConfigInfo {
     pub sysroot_panic_abort: bool,
     pub cg_backend_path: String,
     pub sysroot_path: String,
+    pub gcc_path: String,
+    config_file: Option<String>,
 }
 
 impl ConfigInfo {
@@ -64,6 +135,14 @@ impl ConfigInfo {
                 }
                 _ => return Err("Expected a value after `--out-dir`, found nothing".to_string()),
             },
+            "--config-file" => match args.next() {
+                Some(arg) if !arg.is_empty() => {
+                    self.config_file = Some(arg.to_string());
+                }
+                _ => {
+                    return Err("Expected a value after `--config-file`, found nothing".to_string())
+                }
+            },
             "--release-sysroot" => self.sysroot_release_channel = true,
             "--release" => self.channel = Channel::Release,
             "--sysroot-panic-abort" => self.sysroot_panic_abort = true,
@@ -80,18 +159,46 @@ impl ConfigInfo {
         command
     }
 
+    pub fn setup_gcc_path(&mut self, override_gcc_path: Option<&str>) -> Result<(), String> {
+        let ConfigFile { gcc_path, .. } = ConfigFile::new(self.config_file.as_deref())?;
+
+        self.gcc_path = match override_gcc_path {
+            Some(path) => {
+                if gcc_path.is_some() {
+                    println!(
+                        "overriding setting from `{}`",
+                        self.config_file.as_deref().unwrap_or("config.toml")
+                    );
+                }
+                path.to_string()
+            }
+            None => {
+                match gcc_path {
+                    Some(path) => path,
+                    // FIXME: Once we support "download", rewrite this.
+                    None => {
+                        return Err(format!(
+                            "missing `gcc-path` value from `{}`",
+                            self.config_file.as_deref().unwrap_or("config.toml"),
+                        ))
+                    }
+                }
+            }
+        };
+        Ok(())
+    }
+
     pub fn setup(
         &mut self,
         env: &mut HashMap<String, String>,
-        gcc_path: Option<&str>,
+        override_gcc_path: Option<&str>,
     ) -> Result<(), String> {
         env.insert("CARGO_INCREMENTAL".to_string(), "0".to_string());
 
-        let gcc_path = match gcc_path {
-            Some(path) => path.to_string(),
-            None => get_gcc_path()?,
-        };
-        env.insert("GCC_PATH".to_string(), gcc_path.clone());
+        if self.gcc_path.is_empty() || override_gcc_path.is_some() {
+            self.setup_gcc_path(override_gcc_path)?;
+        }
+        env.insert("GCC_PATH".to_string(), self.gcc_path.clone());
 
         if self.cargo_target_dir.is_empty() {
             match env.get("CARGO_TARGET_DIR").filter(|dir| !dir.is_empty()) {
@@ -225,7 +332,9 @@ impl ConfigInfo {
             // line option to change it.
             target = current_dir.join("target/out").display(),
             sysroot = sysroot.display(),
+            gcc_path = self.gcc_path,
         );
+        env.insert("LIBRARY_PATH".to_string(), ld_library_path.clone());
         env.insert("LD_LIBRARY_PATH".to_string(), ld_library_path.clone());
         env.insert("DYLD_LIBRARY_PATH".to_string(), ld_library_path);
 
@@ -265,7 +374,8 @@ impl ConfigInfo {
     --out-dir              : Location where the files will be generated
     --release              : Build in release mode
     --release-sysroot      : Build sysroot in release mode
-    --sysroot-panic-abort  : Build the sysroot without unwinding support."
+    --sysroot-panic-abort  : Build the sysroot without unwinding support
+    --config-file          : Location of the config file to be used"
         );
     }
 }
diff --git a/build_system/src/test.rs b/build_system/src/test.rs
index 65643229243..1cacd6efc7f 100644
--- a/build_system/src/test.rs
+++ b/build_system/src/test.rs
@@ -1,7 +1,7 @@
 use crate::build;
 use crate::config::{Channel, ConfigInfo};
 use crate::utils::{
-    get_gcc_path, get_toolchain, git_clone, remove_file, run_command, run_command_with_env,
+    get_toolchain, git_clone, remove_file, run_command, run_command_with_env,
     run_command_with_output_and_env, rustc_version_info, split_args, walk_dir,
 };
 
@@ -109,7 +109,7 @@ fn show_usage() {
 struct TestArg {
     no_default_features: bool,
     build_only: bool,
-    gcc_path: String,
+    gcc_path: Option<String>,
     runners: BTreeSet<String>,
     flags: Vec<String>,
     backend: Option<String>,
@@ -181,12 +181,10 @@ impl TestArg {
                 }
             }
 
-            test_arg.gcc_path = if use_system_gcc {
+            if use_system_gcc {
                 println!("Using system GCC");
-                "gcc".to_string()
-            } else {
-                get_gcc_path()?
-            };
+                test_arg.gcc_path = Some("gcc".to_string());
+            }
         }
         match (test_arg.current_part, test_arg.nb_parts) {
             (Some(_), Some(_)) | (None, None) => {}
@@ -488,7 +486,8 @@ fn std_tests(env: &Env, args: &TestArg) -> Result<(), String> {
 }
 
 fn setup_rustc(env: &mut Env, args: &TestArg) -> Result<(), String> {
-    let toolchain = format!("+{channel}-{host}",
+    let toolchain = format!(
+        "+{channel}-{host}",
         channel = get_toolchain()?, // May also include date
         host = args.config_info.host_triple
     );
@@ -527,7 +526,12 @@ fn setup_rustc(env: &mut Env, args: &TestArg) -> Result<(), String> {
         }
     })?;
     let rustc = String::from_utf8(
-        run_command_with_env(&[&"rustup", &toolchain, &"which", &"rustc"], rust_dir, Some(env))?.stdout,
+        run_command_with_env(
+            &[&"rustup", &toolchain, &"which", &"rustc"],
+            rust_dir,
+            Some(env),
+        )?
+        .stdout,
     )
     .map_err(|error| format!("Failed to retrieve rustc path: {:?}", error))
     .and_then(|rustc| {
@@ -1162,8 +1166,15 @@ pub fn run() -> Result<(), String> {
     };
     let mut env: HashMap<String, String> = std::env::vars().collect();
 
-    env.insert("LD_LIBRARY_PATH".to_string(), args.gcc_path.clone());
-    env.insert("LIBRARY_PATH".to_string(), args.gcc_path.clone());
+    args.config_info.setup_gcc_path(None)?;
+    env.insert(
+        "LIBRARY_PATH".to_string(),
+        args.config_info.gcc_path.clone(),
+    );
+    env.insert(
+        "LD_LIBRARY_PATH".to_string(),
+        args.config_info.gcc_path.clone(),
+    );
 
     build_if_no_backend(&env, &args)?;
     if args.build_only {
@@ -1171,7 +1182,7 @@ pub fn run() -> Result<(), String> {
         return Ok(());
     }
 
-    args.config_info.setup(&mut env, Some(&args.gcc_path))?;
+    args.config_info.setup(&mut env, args.gcc_path.as_deref())?;
 
     if args.runners.is_empty() {
         run_all(&env, &args)?;
diff --git a/build_system/src/utils.rs b/build_system/src/utils.rs
index 85f1e18006c..b288eff94a5 100644
--- a/build_system/src/utils.rs
+++ b/build_system/src/utils.rs
@@ -248,38 +248,6 @@ pub fn get_toolchain() -> Result<String, String> {
     }
 }
 
-pub fn get_gcc_path() -> Result<String, String> {
-    let content = match fs::read_to_string("gcc_path") {
-        Ok(content) => content,
-        Err(_) => {
-            return Err(
-                "Please put the path to your custom build of libgccjit in the file \
-                   `gcc_path`, see Readme.md for details"
-                    .into(),
-            )
-        }
-    };
-    match content
-        .split('\n')
-        .map(|line| line.trim())
-        .filter(|line| !line.is_empty())
-        .next()
-    {
-        Some(gcc_path) => {
-            let path = Path::new(gcc_path);
-            if !path.exists() {
-                Err(format!(
-                    "Path `{}` contained in the `gcc_path` file doesn't exist",
-                    gcc_path,
-                ))
-            } else {
-                Ok(gcc_path.into())
-            }
-        }
-        None => Err("No path found in `gcc_path` file".into()),
-    }
-}
-
 pub struct CloneResult {
     pub ran_clone: bool,
     pub repo_name: String,
diff --git a/config.example.toml b/config.example.toml
new file mode 100644
index 00000000000..dcc414b7310
--- /dev/null
+++ b/config.example.toml
@@ -0,0 +1,2 @@
+gcc-path = "gcc-build/gcc"
+# download-gccjit = true
diff --git a/tests/lang_tests_common.rs b/tests/lang_tests_common.rs
index af0133aad46..029a3b98ff2 100644
--- a/tests/lang_tests_common.rs
+++ b/tests/lang_tests_common.rs
@@ -7,6 +7,7 @@ use std::{
 
 use lang_tester::LangTester;
 use tempfile::TempDir;
+use boml::Toml;
 
 /// Controls the compile options (e.g., optimization level) used to compile
 /// test code.
@@ -20,8 +21,16 @@ pub fn main_inner(profile: Profile) {
     let tempdir = TempDir::new().expect("temp dir");
     let current_dir = current_dir().expect("current dir");
     let current_dir = current_dir.to_str().expect("current dir").to_string();
-    let gcc_path = include_str!("../gcc_path");
-    let gcc_path = gcc_path.trim();
+    let gcc_path = Toml::parse(include_str!("../config.toml"))
+        .expect("Failed to parse `config.toml`")
+        .get_string("gcc-path")
+        .expect("Missing `gcc-path` key in `config.toml`")
+        .to_string();
+    let gcc_path = Path::new(&gcc_path)
+        .canonicalize()
+        .expect("failed to get absolute path of `gcc-path`")
+        .display()
+        .to_string();
     env::set_var("LD_LIBRARY_PATH", gcc_path);
 
     fn rust_filter(filename: &Path) -> bool {