Address code review feedback.

* Disable default features for the `byteorder` crate.
* Add a comment regarding the Windows ABI unwind code numerical values.
* Panic if we encounter a Windows function with a prologue greater than 256
  bytes in size.

cranelift-codegen/Cargo.toml

@@ -23,7 +23,7 @@ target-lexicon = "0.8.1"
 log = { version = "0.4.6", default-features = false }
 serde = { version = "1.0.94", features = ["derive"], optional = true }
 smallvec = { version = "0.6.10" }
-byteorder = "1.3.2"
+byteorder = { version = "1.3.2", default-features = false }
 # It is a goal of the cranelift-codegen crate to have minimal external dependencies.
 # Please don't add any unless they are essential to the task of creating binary
 # machine code. Integration tests that need external dependencies can be

cranelift-codegen/src/isa/x86/unwind.rs

@@ -118,7 +118,7 @@ impl UnwindInfo {
         for (offset, inst, size) in func.inst_offsets(entry_block, &isa.encoding_info()) {
             // x64 ABI prologues cannot exceed 256 bytes in length
             if (offset + size) > 256 {
-                return None;
+                panic!("function prologues cannot exceed 256 bytes in size for Windows x64");
             }
 
             prologue_size += size;
@@ -399,7 +399,7 @@ mod tests {
         let mut mem = Vec::new();
         unwind
             .emit(&mut mem)
-            .expect("failed to emit unwind information");;
+            .expect("failed to emit unwind information");
 
         assert_eq!(
             mem,
@@ -465,7 +465,7 @@ mod tests {
         let mut mem = Vec::new();
         unwind
             .emit(&mut mem)
-            .expect("failed to emit unwind information");;
+            .expect("failed to emit unwind information");
 
         assert_eq!(
             mem,

cranelift-filetests/Cargo.toml

@@ -20,7 +20,7 @@ log = "0.4.6"
 memmap = "0.7.0"
 num_cpus = "1.8.0"
 region = "2.1.2"
-byteorder = "1.3.2"
+byteorder = { version = "1.3.2", default-features = false }
 
 [features]
 basic-blocks = []

cranelift-filetests/src/test_unwind.rs

@@ -174,6 +174,7 @@ enum UnwindOperation {
 
 impl From<u8> for UnwindOperation {
     fn from(value: u8) -> Self {
+        // The numerical value is specified as part of the Windows x64 ABI
         match value {
             0 => Self::PushNonvolatileRegister,
             1 => Self::LargeStackAlloc,