Support running on miri

Author: bjorn3

psm/build.rs

@@ -5,7 +5,6 @@ fn find_assembly(
     env: &str,
     masm: bool,
 ) -> Option<(&'static str, bool)> {
-    println!("cargo:rustc-check-cfg=cfg(switchable_stack,asm,link_asm)");
     match (arch, endian, os, env) {
         // The implementations for stack switching exist, but, officially, doing so without Fibers
         // is not supported in Windows. For x86_64 the implementation actually works locally,
@@ -58,6 +57,13 @@ fn find_assembly(
 fn main() {
     use std::env::var;
 
+    println!("cargo:rustc-check-cfg=cfg(switchable_stack,asm,link_asm)");
+
+    if var("CARGO_CFG_MIRI").is_ok() {
+        // Miri doesn't have a stack limit and the inline asm wouldn't work on miri anyway.
+        return;
+    }
+
     let arch = var("CARGO_CFG_TARGET_ARCH").unwrap();
     let env = var("CARGO_CFG_TARGET_ENV").unwrap();
     let os = var("CARGO_CFG_TARGET_OS").unwrap();

src/lib.rs

@@ -268,14 +268,20 @@ psm_stack_manipulation! {
     no {
         #[cfg(not(windows))]
         fn _grow(stack_size: usize, callback: &mut dyn FnMut()) {
-            drop(stack_size);
+            let _ = stack_size;
             callback();
         }
     }
 }
 
 cfg_if! {
-    if #[cfg(windows)] {
+    if #[cfg(miri)] {
+        // Miri doesn't have a stack limit
+        #[inline(always)]
+        unsafe fn guess_os_stack_limit() -> Option<usize> {
+            None
+        }
+    } else if #[cfg(windows)] {
         use std::ptr;
         use std::io;
         use libc::c_void;