Merge pull request #198 from rustbox/opt-level-z-check-prototype

Check for opt-level="z" in `build.rs`, provide feedback about dangers

esp32c3-hal/Cargo.toml

@@ -42,13 +42,14 @@ smart-leds        = "0.3.0"
 ssd1306           = "0.7.1"
 
 [features]
-default     = ["rt", "vectored"]
-direct-boot = []
-eh1         = ["esp-hal-common/eh1", "dep:embedded-hal-1", "dep:embedded-hal-nb"]
-rt          = ["riscv-rt"]
-smartled    = ["esp-hal-common/smartled"]
-ufmt        = ["esp-hal-common/ufmt"]
-vectored    = ["esp-hal-common/vectored"]
+default           = ["rt", "vectored"]
+direct-boot       = []
+eh1               = ["esp-hal-common/eh1", "dep:embedded-hal-1", "dep:embedded-hal-nb"]
+rt                = ["riscv-rt"]
+smartled          = ["esp-hal-common/smartled"]
+ufmt              = ["esp-hal-common/ufmt"]
+vectored          = ["esp-hal-common/vectored"]
+allow-opt-level-z = []
 
 [[example]]
 name              = "hello_rgb"

esp32c3-hal/build.rs

@@ -1,7 +1,9 @@
-use std::{env, fs::File, io::Write, path::PathBuf};
+use std::{env, fs::File, io::Write, path::PathBuf, process::exit};
 
 #[cfg(feature = "direct-boot")]
 fn main() {
+    check_opt_level();
+
     // Put the linker script somewhere the linker can find it
     let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
 
@@ -36,6 +38,8 @@ fn main() {
 
 #[cfg(not(feature = "direct-boot"))]
 fn main() {
+    check_opt_level();
+
     // Put the linker script somewhere the linker can find it
     let out = &PathBuf::from(env::var_os("OUT_DIR").unwrap());
     File::create(out.join("memory.x"))
@@ -71,3 +75,41 @@ fn add_defaults() {
 
     println!("cargo:rustc-link-search={}", out.display());
 }
+
+const OPT_LEVEL_Z_MSG: &str = r#"opt-level=z will produce broken 128-bit shifts (i.e. `1u128 << i`). The hal's interrupt handling relies on that operation, causing an 'attempt to subtract with overflow' panic if an enabled interrupt is triggered while using that opt-level.
+
+Please use `opt-level="s"` in lieu of "z", or alternatively enable `features = ["allow-opt-level-z"]` to suppress this error. The latter option is only recommended if you:
+
+  * Do not use interrupts, and
+  * Do not have any shifts of 128-bit integers (either u128 or i128) in your code
+
+See also: https://github.com/esp-rs/esp-hal/issues/196
+     and: https://github.com/llvm/llvm-project/issues/57988         
+"#;
+
+// Once a rust nightly has a fix for https://github.com/llvm/llvm-project/issues/57988 , consider:
+//   1. Removing this check in favor of bumping the minimum rust verison, and/or
+//   2. Augmenting this check to ensure that version for opt-level=z
+fn check_opt_level() {
+    if cfg!(feature = "allow-opt-level-z") {
+        return;
+    }
+
+    match env::var_os("OPT_LEVEL") {
+        Some(ref opt_level) => {
+            if opt_level == "z" {
+                println!(
+                    "{}",
+                    OPT_LEVEL_Z_MSG
+                        .lines()
+                        .into_iter()
+                        .map(|l| format!("cargo:warning={l}"))
+                        .collect::<Vec<String>>()
+                        .join("\n")
+                );
+                exit(1);
+            }
+        }
+        _ => {}
+    }
+}