more

src/dwarf/divination.rs

@@ -30,9 +30,9 @@ extern "C" {
 #[derive(Debug, Clone, Copy)]
 pub struct DwarfInfo {
     /// The text segment
-    map: *const [u8],
+    pub(super) map: *const [u8],
     /// PT_GNU_EH_FRAME
-    dwarf: *const u8,
+    pub(super) dwarf: *const u8,
 }
 
 pub fn dwarf_info(addr: *const ffi::c_void) -> Option<DwarfInfo> {

src/dwarf/mod.rs

@@ -8,4 +8,6 @@ mod parse;
 
 pub use divination::{dwarf_info, DwarfInfo};
 
-pub fn uwutables(_dwarf_info: DwarfInfo) {}
+pub fn uwutables(dwarf_info: DwarfInfo) {
+    trace!("getting uwutables from {:p}", dwarf_info.dwarf);
+}

src/dwarf/parse.rs

@@ -23,8 +23,10 @@
 //! and the rule to find the value for the previous frame.
 #![allow(non_upper_case_globals)]
 
-struct Expr;
+#[derive(Debug)]
+pub struct Expr;
 
+#[derive(Debug)]
 enum RegisterRule {
     /// A register that has this rule has no recoverable value in the previous frame.
     /// (By convention, it is not preserved by a callee.)
@@ -52,13 +54,15 @@ enum RegisterRule {
 
 type Id = u32;
 
-struct ULeb128(u128);
+#[derive(Debug)]
+pub struct ULeb128(u128);
 impl ULeb128 {
     fn parse() -> Self {
         todo!()
     }
 }
-struct ILeb128(i128);
+#[derive(Debug)]
+pub struct ILeb128(i128);
 impl ILeb128 {
     fn parse() -> Self {
         todo!()
@@ -139,7 +143,8 @@ struct Fde<'a> {
     instructions: &'a [u8],
 }
 
-enum Instruction {
+#[derive(Debug)]
+pub enum Instruction {
     //-------- 6.4.2.1 Row Creation Instructions
     //
     /// The DW_CFA_set_loc instruction takes a single operand that represents a
@@ -318,16 +323,32 @@ enum Instruction {
     Nop,
 }
 
-struct InstrIter<'a> {
-    data: &'a [u8],
+pub(super) struct InstrIter {
+    data: *const u8,
 }
 
-impl<'a> InstrIter<'a> {
+impl InstrIter {
+    /// Create a new `InstrIter` that will parse DWARF call frame information from `data`.
+    /// # Safety
+    /// `data` must be a pointer to valid DWARF call frame information with a null terminator.
+    pub(super) unsafe fn new(data: *const u8) -> Self {
+        Self { data }
+    }
+
     fn advance(&mut self) -> Option<u8> {
-        let (&first, rest) = self.data.split_first()?;
-        self.data = rest;
+        // SAFETY: First, we assume that `data` currently points at a valid location.
+        // After we read from it, we increment it. This has implications. We must assume
+        // that the dwarf parsing code in this module never calls `advance` more than it has to.
+        // This means that really `advance` should be unsafe, but marking it as unsafe would only make
+        // the code in here harder to read and not provide practical safety improvements.
+        // We do eagerly move the data pointer outside the bounds of the allocation, but only one
+        // past the end, which is fine.
+        unsafe {
+            let first = self.data.read();
+            self.data = self.data.add(1);
             Some(first)
         }
+    }
 
     fn uleb128(&mut self) -> ULeb128 {
         ULeb128::parse()
@@ -364,9 +385,10 @@ const DW_CFA_val_expression: u8 = 0x16;
 const DW_CFA_lo_user: u8 = 0x1c;
 const DW_CFA_hi_user: u8 = 0x3f;
 
-impl<'a> Iterator for InstrIter<'a> {
+impl Iterator for InstrIter {
     type Item = Instruction;
 
+    #[allow(unreachable_code)]
     fn next(&mut self) -> Option<Self::Item> {
         let b = self.advance()?;
         let high_2 = b & !(u8::MAX >> 2);

src/lib.rs

@@ -20,8 +20,8 @@ pub unsafe extern "C" fn _UnwindRaiseException(
     exception_object: *mut uw::_Unwind_Exception,
 ) -> uw::_Unwind_Reason_Code {
     trace!("someone raised an exception with addr {exception_object:p}");
-    crate::dwarf::dwarf_info(arch::get_rip() as _);
-
+    let di = crate::dwarf::dwarf_info(arch::get_rip() as _).unwrap();
+    crate::dwarf::uwutables(di);
     // walk::fp::walk();
 
     stdext::abort();