Support referencing stack slots in the DWARF debug info (bytecodealli…

…ance#6960)

* Add a test

* Disable test

* Add support for specifying stack locations in debug info

Always emit SysV-style CFI unwind info if we need debug info,
and reference it in the debug info using DW_OP_call_frame_cfa.

* Add toolchain comment to the test

* Add a comment and assert

cranelift/codegen/src/isa/aarch64/abi.rs

@@ -584,7 +584,7 @@ impl ABIMachineSpec for AArch64MachineDeps {
         insts
     }
 
-    fn gen_prologue_frame_setup(flags: &settings::Flags) -> SmallInstVec<Inst> {
+    fn gen_prologue_frame_setup(flags: &settings::Flags) -> (SmallInstVec<Inst>, u32) {
         let mut insts = SmallVec::new();
 
         // stp fp (x29), lr (x30), [sp, #-16]!
@@ -597,10 +597,11 @@ impl ABIMachineSpec for AArch64MachineDeps {
             flags: MemFlags::trusted(),
         });
 
+        let setup_area_size = 16; // FP, LR
         if flags.unwind_info() {
             insts.push(Inst::Unwind {
                 inst: UnwindInst::PushFrameRegs {
-                    offset_upward_to_caller_sp: 16, // FP, LR
+                    offset_upward_to_caller_sp: setup_area_size,
                 },
             });
         }
@@ -617,7 +618,8 @@ impl ABIMachineSpec for AArch64MachineDeps {
                 shift12: false,
             },
         });
-        insts
+
+        (insts, setup_area_size)
     }
 
     fn gen_epilogue_frame_restore(_: &settings::Flags) -> SmallInstVec<Inst> {

cranelift/codegen/src/isa/aarch64/mod.rs

@@ -132,10 +132,10 @@ impl TargetIsa for AArch64Backend {
     fn emit_unwind_info(
         &self,
         result: &CompiledCode,
-        kind: crate::machinst::UnwindInfoKind,
+        kind: crate::isa::unwind::UnwindInfoKind,
     ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
         use crate::isa::unwind::UnwindInfo;
-        use crate::machinst::UnwindInfoKind;
+        use crate::isa::unwind::UnwindInfoKind;
         Ok(match kind {
             UnwindInfoKind::SystemV => {
                 let mapper = self::inst::unwind::systemv::RegisterMapper;

cranelift/codegen/src/isa/mod.rs

@@ -49,8 +49,8 @@ pub use crate::isa::call_conv::CallConv;
 use crate::flowgraph;
 use crate::ir::{self, Function, Type};
 #[cfg(feature = "unwind")]
-use crate::isa::unwind::systemv::RegisterMappingError;
-use crate::machinst::{CompiledCode, CompiledCodeStencil, TextSectionBuilder, UnwindInfoKind};
+use crate::isa::unwind::{systemv::RegisterMappingError, UnwindInfoKind};
+use crate::machinst::{CompiledCode, CompiledCodeStencil, TextSectionBuilder};
 use crate::settings;
 use crate::settings::SetResult;
 use crate::CodegenResult;

cranelift/codegen/src/isa/riscv64/abi.rs

@@ -341,7 +341,7 @@ impl ABIMachineSpec for Riscv64MachineDeps {
         }
     }
 
-    fn gen_prologue_frame_setup(flags: &settings::Flags) -> SmallInstVec<Inst> {
+    fn gen_prologue_frame_setup(flags: &settings::Flags) -> (SmallInstVec<Self::I>, u32) {
         // add  sp,sp,-16    ;; alloc stack space for fp.
         // sd   ra,8(sp)     ;; save ra.
         // sd   fp,0(sp)     ;; store old fp.
@@ -358,10 +358,12 @@ impl ABIMachineSpec for Riscv64MachineDeps {
             fp_reg(),
             I64,
         ));
+
+        let setup_area_size = 16; // FP, LR
         if flags.unwind_info() {
             insts.push(Inst::Unwind {
                 inst: UnwindInst::PushFrameRegs {
-                    offset_upward_to_caller_sp: 16, // FP, LR
+                    offset_upward_to_caller_sp: setup_area_size,
                 },
             });
         }
@@ -370,7 +372,8 @@ impl ABIMachineSpec for Riscv64MachineDeps {
             rm: stack_reg(),
             ty: I64,
         });
-        insts
+
+        (insts, setup_area_size)
     }
     /// reverse of gen_prologue_frame_setup.
     fn gen_epilogue_frame_restore(_: &settings::Flags) -> SmallInstVec<Inst> {

cranelift/codegen/src/isa/riscv64/mod.rs

@@ -127,10 +127,10 @@ impl TargetIsa for Riscv64Backend {
     fn emit_unwind_info(
         &self,
         result: &CompiledCode,
-        kind: crate::machinst::UnwindInfoKind,
+        kind: crate::isa::unwind::UnwindInfoKind,
     ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
         use crate::isa::unwind::UnwindInfo;
-        use crate::machinst::UnwindInfoKind;
+        use crate::isa::unwind::UnwindInfoKind;
         Ok(match kind {
             UnwindInfoKind::SystemV => {
                 let mapper = self::inst::unwind::systemv::RegisterMapper;

cranelift/codegen/src/isa/s390x/abi.rs

@@ -556,8 +556,8 @@ impl ABIMachineSpec for S390xMachineDeps {
         }
     }
 
-    fn gen_prologue_frame_setup(_flags: &settings::Flags) -> SmallInstVec<Inst> {
-        SmallVec::new()
+    fn gen_prologue_frame_setup(_flags: &settings::Flags) -> (SmallInstVec<Inst>, u32) {
+        (SmallVec::new(), 0)
     }
 
     fn gen_epilogue_frame_restore(_flags: &settings::Flags) -> SmallInstVec<Inst> {

cranelift/codegen/src/isa/s390x/mod.rs

@@ -129,10 +129,10 @@ impl TargetIsa for S390xBackend {
     fn emit_unwind_info(
         &self,
         result: &CompiledCode,
-        kind: crate::machinst::UnwindInfoKind,
+        kind: crate::isa::unwind::UnwindInfoKind,
     ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
         use crate::isa::unwind::UnwindInfo;
-        use crate::machinst::UnwindInfoKind;
+        use crate::isa::unwind::UnwindInfoKind;
         Ok(match kind {
             UnwindInfoKind::SystemV => {
                 let mapper = self::inst::unwind::systemv::RegisterMapper;

cranelift/codegen/src/isa/unwind.rs

@@ -11,6 +11,23 @@ pub mod systemv;
 #[cfg(feature = "unwind")]
 pub mod winx64;
 
+/// CFA-based unwind information used on SystemV.
+pub type CfaUnwindInfo = systemv::UnwindInfo;
+
+/// Expected unwind info type.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[non_exhaustive]
+pub enum UnwindInfoKind {
+    /// No unwind info.
+    None,
+    /// SystemV CIE/FDE unwind info.
+    #[cfg(feature = "unwind")]
+    SystemV,
+    /// Windows X64 Unwind info
+    #[cfg(feature = "unwind")]
+    Windows,
+}
+
 /// Represents unwind information for a single function.
 #[derive(Clone, Debug, PartialEq, Eq)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
@@ -21,7 +38,7 @@ pub enum UnwindInfo {
     WindowsX64(winx64::UnwindInfo),
     /// System V ABI unwind information.
     #[cfg(feature = "unwind")]
-    SystemV(systemv::UnwindInfo),
+    SystemV(CfaUnwindInfo),
 }
 
 /// Unwind pseudoinstruction used in VCode backends: represents that

cranelift/codegen/src/isa/unwind/systemv.rs

@@ -161,6 +161,12 @@ pub struct UnwindInfo {
     len: u32,
 }
 
+/// Offset from the caller's SP to CFA as we define it.
+pub(crate) fn caller_sp_to_cfa_offset() -> u32 {
+    // Currently we define them to always be equal.
+    0
+}
+
 pub(crate) fn create_unwind_info_from_insts<MR: RegisterMapper<Reg>>(
     insts: &[(CodeOffset, UnwindInst)],
     code_len: usize,

cranelift/codegen/src/isa/x64/abi.rs

@@ -444,7 +444,7 @@ impl ABIMachineSpec for X64ABIMachineSpec {
         }
     }
 
-    fn gen_prologue_frame_setup(flags: &settings::Flags) -> SmallInstVec<Self::I> {
+    fn gen_prologue_frame_setup(flags: &settings::Flags) -> (SmallInstVec<Self::I>, u32) {
         let r_rsp = regs::rsp();
         let r_rbp = regs::rbp();
         let w_rbp = Writable::from_reg(r_rbp);
@@ -453,18 +453,20 @@ impl ABIMachineSpec for X64ABIMachineSpec {
         // RSP before the call will be 0 % 16.  So here, it is 8 % 16.
         insts.push(Inst::push64(RegMemImm::reg(r_rbp)));
 
+        let setup_area_size = 16; // RBP, return address
         if flags.unwind_info() {
             insts.push(Inst::Unwind {
                 inst: UnwindInst::PushFrameRegs {
-                    offset_upward_to_caller_sp: 16, // RBP, return address
+                    offset_upward_to_caller_sp: setup_area_size,
                 },
             });
         }
 
         // `mov %rsp, %rbp`
         // RSP is now 0 % 16
         insts.push(Inst::mov_r_r(OperandSize::Size64, r_rsp, w_rbp));
-        insts
+
+        (insts, setup_area_size)
     }
 
     fn gen_epilogue_frame_restore(_: &settings::Flags) -> SmallInstVec<Self::I> {

cranelift/codegen/src/isa/x64/mod.rs

@@ -123,10 +123,10 @@ impl TargetIsa for X64Backend {
     fn emit_unwind_info(
         &self,
         result: &CompiledCode,
-        kind: crate::machinst::UnwindInfoKind,
+        kind: crate::isa::unwind::UnwindInfoKind,
     ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
         use crate::isa::unwind::UnwindInfo;
-        use crate::machinst::UnwindInfoKind;
+        use crate::isa::unwind::UnwindInfoKind;
         Ok(match kind {
             UnwindInfoKind::SystemV => {
                 let mapper = self::inst::unwind::systemv::RegisterMapper;

cranelift/codegen/src/machinst/abi.rs

@@ -522,8 +522,8 @@ pub trait ABIMachineSpec {
 
     /// Generate the usual frame-setup sequence for this architecture: e.g.,
     /// `push rbp / mov rbp, rsp` on x86-64, or `stp fp, lr, [sp, #-16]!` on
-    /// AArch64.
-    fn gen_prologue_frame_setup(flags: &settings::Flags) -> SmallInstVec<Self::I>;
+    /// AArch64. Return generated instructions and stack size of the setup area.
+    fn gen_prologue_frame_setup(flags: &settings::Flags) -> (SmallInstVec<Self::I>, u32);
 
     /// Generate the usual frame-restore sequence for this architecture.
     fn gen_epilogue_frame_restore(flags: &settings::Flags) -> SmallInstVec<Self::I>;
@@ -1021,6 +1021,9 @@ pub struct Callee<M: ABIMachineSpec> {
     /// Storage allocated for the fixed part of the stack frame.  This is
     /// usually the same as the total frame size below.
     fixed_frame_storage_size: u32,
+    /// Size of the area between the FP as defined in the prolog and caller's SP.
+    /// It will usually contain the saved FP/LR pair.
+    frame_setup_area_size: u32,
     /// "Total frame size", as defined by "distance between FP and nominal SP".
     /// Some items are pushed below nominal SP, so the function may actually use
     /// more stack than this would otherwise imply. It is simply the initial
@@ -1185,6 +1188,7 @@ impl<M: ABIMachineSpec> Callee<M> {
             clobbered: vec![],
             spillslots: None,
             fixed_frame_storage_size: 0,
+            frame_setup_area_size: 0,
             total_frame_size: None,
             ret_area_ptr: None,
             arg_temp_reg: vec![],
@@ -1760,10 +1764,7 @@ impl<M: ABIMachineSpec> Callee<M> {
         ty: Type,
         into_regs: ValueRegs<Writable<Reg>>,
     ) -> SmallInstVec<M::I> {
-        // Offset from beginning of spillslot area, which is at nominal SP + stackslots_size.
-        let islot = slot.index() as i64;
-        let spill_off = islot * M::word_bytes() as i64;
-        let sp_off = self.stackslots_size as i64 + spill_off;
+        let sp_off = self.get_spillslot_offset(slot);
         trace!("load_spillslot: slot {:?} -> sp_off {}", slot, sp_off);
 
         gen_load_stack_multi::<M>(StackAMode::NominalSPOffset(sp_off, ty), into_regs, ty)
@@ -1776,10 +1777,7 @@ impl<M: ABIMachineSpec> Callee<M> {
         ty: Type,
         from_regs: ValueRegs<Reg>,
     ) -> SmallInstVec<M::I> {
-        // Offset from beginning of spillslot area, which is at nominal SP + stackslots_size.
-        let islot = slot.index() as i64;
-        let spill_off = islot * M::word_bytes() as i64;
-        let sp_off = self.stackslots_size as i64 + spill_off;
+        let sp_off = self.get_spillslot_offset(slot);
         trace!("store_spillslot: slot {:?} -> sp_off {}", slot, sp_off);
 
         gen_store_stack_multi::<M>(StackAMode::NominalSPOffset(sp_off, ty), from_regs, ty)
@@ -1890,8 +1888,9 @@ impl<M: ABIMachineSpec> Callee<M> {
         );
 
         if self.setup_frame {
-            // set up frame
-            insts.extend(M::gen_prologue_frame_setup(&self.flags).into_iter());
+            let (setup_insts, setup_area_size) = M::gen_prologue_frame_setup(&self.flags);
+            insts.extend(setup_insts.into_iter());
+            self.frame_setup_area_size = setup_area_size;
         }
 
         // Leaf functions with zero stack don't need a stack check if one's
@@ -1992,14 +1991,20 @@ impl<M: ABIMachineSpec> Callee<M> {
     }
 
     /// Returns the full frame size for the given function, after prologue
-    /// emission has run. This comprises the spill slots and stack-storage slots
-    /// (but not storage for clobbered callee-save registers, arguments pushed
-    /// at callsites within this function, or other ephemeral pushes).
+    /// emission has run. This comprises the spill slots and stack-storage
+    /// slots as well as storage for clobbered callee-save registers, but
+    /// not arguments arguments pushed at callsites within this function,
+    /// or other ephemeral pushes.
     pub fn frame_size(&self) -> u32 {
         self.total_frame_size
             .expect("frame size not computed before prologue generation")
     }
 
+    /// Returns offset from the nominal SP to caller's SP.
+    pub fn nominal_sp_to_caller_sp_offset(&self) -> u32 {
+        self.frame_size() + self.frame_setup_area_size
+    }
+
     /// Returns the size of arguments expected on the stack.
     pub fn stack_args_size(&self, sigs: &SigSet) -> u32 {
         sigs[self.sig].sized_stack_arg_space
@@ -2020,6 +2025,16 @@ impl<M: ABIMachineSpec> Callee<M> {
         M::get_number_of_spillslots_for_value(rc, max, &self.isa_flags)
     }
 
+    /// Get the spill slot offset relative to nominal SP.
+    pub fn get_spillslot_offset(&self, slot: SpillSlot) -> i64 {
+        // Offset from beginning of spillslot area, which is at nominal SP + stackslots_size.
+        let islot = slot.index() as i64;
+        let spill_off = islot * M::word_bytes() as i64;
+        let sp_off = self.stackslots_size as i64 + spill_off;
+
+        sp_off
+    }
+
     /// Generate a spill.
     pub fn gen_spill(&self, to_slot: SpillSlot, from_reg: RealReg) -> M::I {
         let ty = M::I::canonical_type_for_rc(Reg::from(from_reg).class());

cranelift/codegen/src/machinst/mod.rs

@@ -482,10 +482,24 @@ impl CompiledCode {
         &self,
         isa: &dyn crate::isa::TargetIsa,
     ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
+        use crate::isa::unwind::UnwindInfoKind;
         let unwind_info_kind = match isa.triple().operating_system {
             target_lexicon::OperatingSystem::Windows => UnwindInfoKind::Windows,
             _ => UnwindInfoKind::SystemV,
         };
+        self.create_unwind_info_of_kind(isa, unwind_info_kind)
+    }
+
+    /// Creates unwind information for the function using the supplied
+    /// "kind". Supports cross-OS (but not cross-arch) generation.
+    ///
+    /// Returns `None` if the function has no unwind information.
+    #[cfg(feature = "unwind")]
+    pub fn create_unwind_info_of_kind(
+        &self,
+        isa: &dyn crate::isa::TargetIsa,
+        unwind_info_kind: crate::isa::unwind::UnwindInfoKind,
+    ) -> CodegenResult<Option<crate::isa::unwind::UnwindInfo>> {
         isa.emit_unwind_info(self, unwind_info_kind)
     }
 }
@@ -537,17 +551,3 @@ pub trait TextSectionBuilder {
     /// the bytes of the text section.
     fn finish(&mut self, ctrl_plane: &mut ControlPlane) -> Vec<u8>;
 }
-
-/// Expected unwind info type.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-#[non_exhaustive]
-pub enum UnwindInfoKind {
-    /// No unwind info.
-    None,
-    /// SystemV CIE/FDE unwind info.
-    #[cfg(feature = "unwind")]
-    SystemV,
-    /// Windows X64 Unwind info
-    #[cfg(feature = "unwind")]
-    Windows,
-}