Implement emitting Windows unwind information for fastcall functions.

cranelift-codegen/Cargo.toml

@@ -22,6 +22,7 @@ log = { version = "0.4.6", default-features = false }
 serde = { version = "1.0.94", features = ["derive"], optional = true }
 smallvec = { version = "0.6.10" }
 thiserror = "1.0.4"
+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/context.rs

@@ -193,6 +193,16 @@ impl Context {
         sink.info
     }
 
+    /// Emit unwind information.
+    ///
+    /// Requires that the function layout be calculated (see `relax_branches`).
+    ///
+    /// Only some calling conventions (e.g. Windows fastcall) will have unwind information.
+    /// This is a no-op if the function has no unwind information.
+    pub fn emit_unwind_info(&self, isa: &dyn TargetIsa, mem: &mut Vec<u8>) {
+        isa.emit_unwind_info(&self.func, mem);
+    }
+
     /// Run the verifier on the function.
     ///
     /// Also check that the dominator tree and control flow graph are consistent with the function.

cranelift-codegen/src/ir/function.rs

@@ -83,6 +83,11 @@ pub struct Function {
     /// Track the original source location for each instruction. The source locations are not
     /// interpreted by Cranelift, only preserved.
     pub srclocs: SourceLocs,
+
+    /// Instruction that marks the end (inclusive) of the function's prologue.
+    ///
+    /// This is used for some calling conventions to track the end of unwind information.
+    pub prologue_end: Option<Inst>,
 }
 
 impl Function {
@@ -104,6 +109,7 @@ impl Function {
             offsets: SecondaryMap::new(),
             jt_offsets: SecondaryMap::new(),
             srclocs: SecondaryMap::new(),
+            prologue_end: None,
         }
     }
 
@@ -123,6 +129,7 @@ impl Function {
         self.offsets.clear();
         self.jt_offsets.clear();
         self.srclocs.clear();
+        self.prologue_end = None;
     }
 
     /// Create a new empty, anonymous function with a Fast calling convention.

cranelift-codegen/src/isa/mod.rs

@@ -64,6 +64,7 @@ use crate::settings;
 use crate::settings::SetResult;
 use crate::timing;
 use alloc::boxed::Box;
+use alloc::vec::Vec;
 use core::fmt;
 use target_lexicon::{triple, Architecture, PointerWidth, Triple};
 use thiserror::Error;
@@ -377,4 +378,11 @@ pub trait TargetIsa: fmt::Display + Sync {
 
     /// IntCC condition for Unsigned Subtraction Overflow (Borrow/Carry).
     fn unsigned_sub_overflow_condition(&self) -> ir::condcodes::IntCC;
+
+    /// Emit unwind information for the given function.
+    ///
+    /// Only some calling conventions (e.g. Windows fastcall) will have unwind information.
+    fn emit_unwind_info(&self, _func: &ir::Function, _mem: &mut Vec<u8>) {
+        // No-op by default
+    }
 }

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

@@ -3,6 +3,7 @@
 use super::super::settings as shared_settings;
 use super::registers::{FPR, GPR, RU};
 use super::settings as isa_settings;
+use super::unwind::UnwindInfo;
 use crate::abi::{legalize_args, ArgAction, ArgAssigner, ValueConversion};
 use crate::cursor::{Cursor, CursorPosition, EncCursor};
 use crate::ir;
@@ -16,6 +17,7 @@ use crate::isa::{CallConv, RegClass, RegUnit, TargetIsa};
 use crate::regalloc::RegisterSet;
 use crate::result::CodegenResult;
 use crate::stack_layout::layout_stack;
+use alloc::vec::Vec;
 use core::i32;
 use target_lexicon::{PointerWidth, Triple};
 
@@ -269,7 +271,7 @@ fn callee_saved_gprs(isa: &dyn TargetIsa, call_conv: CallConv) -> &'static [RU]
             if call_conv.extends_windows_fastcall() {
                 // "registers RBX, RBP, RDI, RSI, RSP, R12, R13, R14, R15 are considered nonvolatile
                 //  and must be saved and restored by a function that uses them."
-                // as per https://msdn.microsoft.com/en-us/library/6t169e9c.aspx
+                // as per https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention
                 // RSP & RSB are not listed below, since they are restored automatically during
                 // a function call. If that wasn't the case, function calls (RET) would not work.
                 &[
@@ -372,7 +374,7 @@ fn baldrdash_prologue_epilogue(func: &mut ir::Function, isa: &dyn TargetIsa) ->
 }
 
 /// Implementation of the fastcall-based Win64 calling convention described at [1]
-/// [1] https://msdn.microsoft.com/en-us/library/ms235286.aspx
+/// [1] https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention
 fn fastcall_prologue_epilogue(func: &mut ir::Function, isa: &dyn TargetIsa) -> CodegenResult<()> {
     if isa.triple().pointer_width().unwrap() != PointerWidth::U64 {
         panic!("TODO: windows-fastcall: x86-32 not implemented yet");
@@ -580,11 +582,11 @@ fn insert_common_prologue(
             if !isa.flags().probestack_func_adjusts_sp() {
                 let result = pos.func.dfg.inst_results(call)[0];
                 pos.func.locations[result] = rax_val;
-                pos.ins().adjust_sp_down(result);
+                pos.func.prologue_end = Some(pos.ins().adjust_sp_down(result));
             }
         } else {
             // Simply decrement the stack pointer.
-            pos.ins().adjust_sp_down_imm(Imm64::new(stack_size));
+            pos.func.prologue_end = Some(pos.ins().adjust_sp_down_imm(Imm64::new(stack_size)));
         }
     }
 }
@@ -658,3 +660,11 @@ fn insert_common_epilogue(
         pos.func.dfg.append_inst_arg(inst, csr_ret);
     }
 }
+
+pub fn emit_unwind_info(func: &ir::Function, isa: &dyn TargetIsa, mem: &mut Vec<u8>) {
+    // Assumption: RBP is being used as the frame pointer
+    // In the future, Windows fastcall codegen should usually omit the frame pointer
+    if let Some(info) = UnwindInfo::try_from_func(func, isa, Some(RU::rbp.into())) {
+        info.emit(mem).expect("failed to emit unwind information");
+    }
+}

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

@@ -5,6 +5,7 @@ mod binemit;
 mod enc_tables;
 mod registers;
 pub mod settings;
+mod unwind;
 
 use super::super::settings as shared_settings;
 #[cfg(feature = "testing_hooks")]
@@ -18,6 +19,7 @@ use crate::regalloc;
 use crate::result::CodegenResult;
 use crate::timing;
 use alloc::boxed::Box;
+use alloc::vec::Vec;
 use core::fmt;
 use target_lexicon::{PointerWidth, Triple};
 
@@ -150,6 +152,13 @@ impl TargetIsa for Isa {
     fn unsigned_sub_overflow_condition(&self) -> ir::condcodes::IntCC {
         ir::condcodes::IntCC::UnsignedLessThan
     }
+
+    /// Emit unwind information for the given function.
+    ///
+    /// Only some calling conventions (e.g. Windows fastcall) will have unwind information.
+    fn emit_unwind_info(&self, func: &ir::Function, mem: &mut Vec<u8>) {
+        abi::emit_unwind_info(func, self, mem);
+    }
 }
 
 impl fmt::Display for Isa {