Refactor unwind generation in Cranelift.

cranelift/codegen/src/binemit/mod.rs

@@ -173,36 +173,6 @@ pub trait CodeSink {
     }
 }
 
-/// Type of the frame unwind information.
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-pub enum FrameUnwindKind {
-    /// Windows fastcall unwinding (as in .pdata).
-    Fastcall,
-    /// FDE entry for libunwind (similar to .eh_frame format).
-    Libunwind,
-}
-
-/// Offset in frame unwind information buffer.
-pub type FrameUnwindOffset = usize;
-
-/// Sink for frame unwind information.
-pub trait FrameUnwindSink {
-    /// Get the current position.
-    fn len(&self) -> FrameUnwindOffset;
-
-    /// Add bytes to the code section.
-    fn bytes(&mut self, _: &[u8]);
-
-    /// Reserves bytes in the buffer.
-    fn reserve(&mut self, _len: usize) {}
-
-    /// Add a relocation entry.
-    fn reloc(&mut self, _: Reloc, _: FrameUnwindOffset);
-
-    /// Specified offset to main structure.
-    fn set_entry_offset(&mut self, _: FrameUnwindOffset);
-}
-
 /// Report a bad encoding error.
 #[cold]
 pub fn bad_encoding(func: &Function, inst: Inst) -> ! {

cranelift/codegen/src/context.rs

@@ -10,8 +10,8 @@
 //! single ISA instance.
 
 use crate::binemit::{
-    relax_branches, shrink_instructions, CodeInfo, FrameUnwindKind, FrameUnwindSink,
-    MemoryCodeSink, RelocSink, StackmapSink, TrapSink,
+    relax_branches, shrink_instructions, CodeInfo, MemoryCodeSink, RelocSink, StackmapSink,
+    TrapSink,
 };
 use crate::dce::do_dce;
 use crate::dominator_tree::DominatorTree;
@@ -231,19 +231,15 @@ impl Context {
         sink.info
     }
 
-    /// Emit unwind information.
+    /// Creates unwind information for the function.
     ///
-    /// 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(
+    /// Returns `None` if the function has no unwind information.
+    #[cfg(feature = "unwind")]
+    pub fn create_unwind_info(
         &self,
         isa: &dyn TargetIsa,
-        kind: FrameUnwindKind,
-        sink: &mut dyn FrameUnwindSink,
-    ) -> CodegenResult<()> {
-        isa.emit_unwind_info(&self.func, kind, sink)
+    ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
+        isa.create_unwind_info(&self.func)
     }
 
     /// Run the verifier on the function.

cranelift/codegen/src/ir/function.rs

@@ -10,13 +10,14 @@ use crate::ir::{
     Block, ExtFuncData, FuncRef, GlobalValue, GlobalValueData, Heap, HeapData, Inst, JumpTable,
     JumpTableData, Opcode, SigRef, StackSlot, StackSlotData, Table, TableData,
 };
-use crate::ir::{BlockOffsets, FrameLayout, InstEncodings, SourceLocs, StackSlots, ValueLocations};
+use crate::ir::{BlockOffsets, InstEncodings, SourceLocs, StackSlots, ValueLocations};
 use crate::ir::{DataFlowGraph, ExternalName, Layout, Signature};
 use crate::ir::{JumpTableOffsets, JumpTables};
 use crate::isa::{CallConv, EncInfo, Encoding, Legalize, TargetIsa};
 use crate::regalloc::{EntryRegDiversions, RegDiversions};
 use crate::value_label::ValueLabelsRanges;
 use crate::write::write_function;
+use alloc::vec::Vec;
 use core::fmt;
 
 /// A function.
@@ -87,15 +88,13 @@ pub struct Function {
 
     /// 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.
+    /// This is used for some ABIs to generate unwind information.
     pub prologue_end: Option<Inst>,
 
-    /// Frame layout for the instructions.
+    /// The instructions that mark the start (inclusive) of an epilogue in the function.
     ///
-    /// The stack unwinding requires to have information about which registers and where they
-    /// are saved in the frame. This information is created during the prologue and epilogue
-    /// passes.
-    pub frame_layout: Option<FrameLayout>,
+    /// This is used for some ABIs to generate unwind information.
+    pub epilogues_start: Vec<Inst>,
 }
 
 impl Function {
@@ -119,7 +118,7 @@ impl Function {
             jt_offsets: SecondaryMap::new(),
             srclocs: SecondaryMap::new(),
             prologue_end: None,
-            frame_layout: None,
+            epilogues_start: Vec::new(),
         }
     }
 
@@ -140,7 +139,7 @@ impl Function {
         self.jt_offsets.clear();
         self.srclocs.clear();
         self.prologue_end = None;
-        self.frame_layout = None;
+        self.epilogues_start.clear();
     }
 
     /// Create a new empty, anonymous function with a Fast calling convention.
@@ -258,12 +257,6 @@ impl Function {
     /// Starts collection of debug information.
     pub fn collect_debug_info(&mut self) {
         self.dfg.collect_debug_info();
-        self.collect_frame_layout_info();
-    }
-
-    /// Starts collection of frame layout information.
-    pub fn collect_frame_layout_info(&mut self) {
-        self.frame_layout = Some(FrameLayout::new());
     }
 
     /// Changes the destination of a jump or branch instruction.

cranelift/codegen/src/ir/mod.rs

@@ -6,7 +6,6 @@ pub mod dfg;
 pub mod entities;
 mod extfunc;
 mod extname;
-mod framelayout;
 pub mod function;
 mod globalvalue;
 mod heap;
@@ -40,7 +39,6 @@ pub use crate::ir::extfunc::{
     AbiParam, ArgumentExtension, ArgumentPurpose, ExtFuncData, Signature,
 };
 pub use crate::ir::extname::ExternalName;
-pub use crate::ir::framelayout::{FrameLayout, FrameLayoutChange, FrameLayoutChanges};
 pub use crate::ir::function::{DisplayFunctionAnnotations, Function};
 pub use crate::ir::globalvalue::GlobalValueData;
 pub use crate::ir::heap::{HeapData, HeapStyle};

cranelift/codegen/src/isa/mod.rs

@@ -56,8 +56,8 @@ pub use crate::isa::stack::{StackBase, StackBaseMask, StackRef};
 use crate::binemit;
 use crate::flowgraph;
 use crate::ir;
-use crate::isa::fde::RegisterMappingError;
 #[cfg(feature = "unwind")]
+use crate::isa::unwind::systemv::RegisterMappingError;
 use crate::machinst::MachBackend;
 use crate::regalloc;
 use crate::result::CodegenResult;
@@ -77,15 +77,15 @@ mod riscv;
 #[cfg(feature = "x86")]
 mod x86;
 
-#[cfg(feature = "unwind")]
-pub mod fde;
-
 #[cfg(feature = "arm32")]
 mod arm32;
 
 #[cfg(feature = "arm64")]
 mod aarch64;
 
+#[cfg(feature = "unwind")]
+pub mod unwind;
+
 mod call_conv;
 mod constraints;
 mod enc_tables;
@@ -394,17 +394,25 @@ pub trait TargetIsa: fmt::Display + Send + 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.
+    /// Creates unwind information for the function.
     ///
-    /// Only some calling conventions (e.g. Windows fastcall) will have unwind information.
-    fn emit_unwind_info(
+    /// Returns `None` if there is no unwind information for the function.
+    #[cfg(feature = "unwind")]
+    fn create_unwind_info(
         &self,
         _func: &ir::Function,
-        _kind: binemit::FrameUnwindKind,
-        _sink: &mut dyn binemit::FrameUnwindSink,
-    ) -> CodegenResult<()> {
-        // No-op by default
-        Ok(())
+    ) -> CodegenResult<Option<unwind::UnwindInfo>> {
+        // By default, an ISA has no unwind information
+        Ok(None)
+    }
+
+    /// Creates a new System V Common Information Entry for the ISA.
+    ///
+    /// Returns `None` if the ISA does not support System V unwind information.
+    #[cfg(feature = "unwind")]
+    fn create_systemv_cie(&self) -> Option<gimli::write::CommonInformationEntry> {
+        // By default, an ISA cannot create a System V CIE
+        None
     }
 
     /// Get the new-style MachBackend, if this is an adapter around one.

cranelift/codegen/src/isa/unwind.rs

@@ -0,0 +1,16 @@
+//! Represents information relating to function unwinding.
+#[cfg(feature = "enable-serde")]
+use serde::{Deserialize, Serialize};
+
+pub mod systemv;
+pub mod winx64;
+
+/// Represents unwind information for a single function.
+#[derive(Clone, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
+pub enum UnwindInfo {
+    /// Windows x64 ABI unwind information.
+    WindowsX64(winx64::UnwindInfo),
+    /// System V ABI unwind information.
+    SystemV(systemv::UnwindInfo),
+}