Properly handle DW_CFA_GNU_args_size

examples/dwarfdump.rs

@@ -610,6 +610,9 @@ fn dump_cfi_instructions<R: Reader, W: Write>(
                 RestoreState => {
                     writeln!(w, "                DW_CFA_restore_state")?;
                 }
+                ArgsSize { size } => {
+                    writeln!(w, "                DW_CFA_GNU_args_size ({})", size)?;
+                }
                 Nop => {
                     writeln!(w, "                DW_CFA_nop")?;
                 }

src/cfi.rs

@@ -2283,6 +2283,12 @@ where
                 self.ctx.set_start_address(start_address);
             }
 
+            // GNU Extension. Save the size somewhere so the unwinder can use
+            // it when restoring IP
+            ArgsSize { size } => {
+                self.ctx.row_mut().saved_args_size = size;
+            }
+
             // No operation.
             Nop => {}
         };
@@ -2439,6 +2445,7 @@ impl<'iter, R: Reader> Iterator for RegisterRuleIter<'iter, R> {
 pub struct UnwindTableRow<R: Reader> {
     start_address: u64,
     end_address: u64,
+    saved_args_size: u64,
     cfa: CfaRule<R>,
     registers: RegisterRuleMap<R>,
 }
@@ -2448,6 +2455,7 @@ impl<R: Reader> Default for UnwindTableRow<R> {
         UnwindTableRow {
             start_address: 0,
             end_address: 0,
+            saved_args_size: 0,
             cfa: Default::default(),
             registers: Default::default(),
         }
@@ -2482,6 +2490,14 @@ impl<R: Reader> UnwindTableRow<R> {
         self.start_address <= address && address < self.end_address
     }
 
+    /// Returns the amount of args currently on the stack.
+    ///
+    /// When unwinding, if the personality function requested a change in IP,
+    /// the SP needs to be adjusted by saved_args_size.
+    pub fn saved_args_size(&self) -> u64 {
+        self.saved_args_size
+    }
+
     /// Get the canonical frame address (CFA) recovery rule for this row.
     pub fn cfa(&self) -> &CfaRule<R> {
         &self.cfa
@@ -2905,6 +2921,19 @@ pub enum CallFrameInstruction<R: Reader> {
     /// > them in the current row.
     RestoreState,
 
+
+    /// > DW_CFA_GNU_args_size
+    /// > 
+    /// > GNU Extension
+    /// >
+    /// > The DW_CFA_GNU_args_size instruction takes an unsigned LEB128 operand
+    /// > representing an argument size. This instruction specifies the total of
+    /// > the size of the arguments which have been pushed onto the stack.
+    ArgsSize {
+        /// The size of the arguments which have been pushed onto the stack
+        size: u64
+    },
+
     // 6.4.2.5 Padding Instruction
     /// > 1. DW_CFA_nop
     /// >
@@ -3099,6 +3128,13 @@ impl<R: Reader> CallFrameInstruction<R> {
                 })
             }
 
+            constants::DW_CFA_GNU_args_size => {
+                let size = input.read_uleb128()?;
+                Ok(CallFrameInstruction::ArgsSize {
+                    size
+                })
+            }
+
             otherwise => Err(Error::UnknownCallFrameInstruction(otherwise)),
         }
     }
@@ -5196,6 +5232,7 @@ mod tests {
             let expected = UnwindTableRow {
                 start_address: 0,
                 end_address: 1,
+                saved_args_size: 0,
                 cfa: CfaRule::RegisterAndOffset {
                     register: 4,
                     offset: -12,
@@ -5212,6 +5249,7 @@ mod tests {
             let expected = UnwindTableRow {
                 start_address: 1,
                 end_address: 33,
+                saved_args_size: 0,
                 cfa: CfaRule::RegisterAndOffset {
                     register: 4,
                     offset: -12,
@@ -5228,6 +5266,7 @@ mod tests {
             let expected = UnwindTableRow {
                 start_address: 33,
                 end_address: 97,
+                saved_args_size: 0,
                 cfa: CfaRule::RegisterAndOffset {
                     register: 4,
                     offset: -12,
@@ -5246,6 +5285,7 @@ mod tests {
             let expected = UnwindTableRow {
                 start_address: 97,
                 end_address: 100,
+                saved_args_size: 0,
                 cfa: CfaRule::RegisterAndOffset {
                     register: 4,
                     offset: -12,
@@ -5376,6 +5416,7 @@ mod tests {
             UnwindTableRow {
                 start_address: fde1.initial_address() + 100,
                 end_address: fde1.initial_address() + fde1.len(),
+                saved_args_size: 0,
                 cfa: CfaRule::RegisterAndOffset {
                     register: 4,
                     offset: -12,
@@ -6163,7 +6204,7 @@ mod tests {
             mem::size_of::<
                 UnwindContext<EhFrame<EndianSlice<NativeEndian>>, EndianSlice<NativeEndian>>,
             >(),
-            5384
+            5416
         );
     }