From ebfd4209fe82a2ad70df2b32fd8e4f11f878048e Mon Sep 17 00:00:00 2001
From: Chris Fallin <chris@cfallin.org>
Date: Mon, 13 Feb 2023 17:02:25 -0800
Subject: [PATCH] WIP.

---
 src/frontend.rs |  9 +++++++--
 src/ir/debug.rs | 22 +++-------------------
 2 files changed, 10 insertions(+), 21 deletions(-)

diff --git a/src/frontend.rs b/src/frontend.rs
index 891dcff..6b28d2c 100644
--- a/src/frontend.rs
+++ b/src/frontend.rs
@@ -358,18 +358,23 @@ fn handle_payload<'a>(
 }
 
 struct DebugLocReader<'a> {
+    code_section_offset: u32,
     locs: &'a [(u32, u32, SourceLoc)],
 }
 
 impl<'a> DebugLocReader<'a> {
     fn new(module: &'a Module, offset: usize) -> Self {
         DebugLocReader {
-            locs: module.debug_map.locs_from_offset(offset),
+            code_section_offset: u32::try_from(offset).unwrap(),
+            locs: &module.debug_map.tuples[..],
         }
     }
 
     fn get_loc(&mut self, offset: usize) -> SourceLoc {
-        let offset = u32::try_from(offset).unwrap();
+        let offset = u32::try_from(offset)
+            .unwrap()
+            .checked_sub(self.code_section_offset)
+            .unwrap();
         while self.locs.len() > 0 {
             let (start, len, loc) = self.locs[0];
             if offset < start {
diff --git a/src/ir/debug.rs b/src/ir/debug.rs
index 969de8c..e7365ce 100644
--- a/src/ir/debug.rs
+++ b/src/ir/debug.rs
@@ -5,7 +5,6 @@ use crate::entity::EntityVec;
 use addr2line::gimli;
 use std::collections::hash_map::Entry as HashEntry;
 use std::collections::HashMap;
-use std::convert::TryFrom;
 
 declare_entity!(SourceFile, "file");
 declare_entity!(SourceLoc, "loc");
@@ -49,7 +48,9 @@ impl Debug {
 
 #[derive(Clone, Debug, Default)]
 pub struct DebugMap {
-    tuples: Vec<(u32, u32, SourceLoc)>,
+    /// Each tuple is `(start, len, loc)`. The `start` offset is
+    /// relative to the Wasm code section (*not* the entire file).
+    pub tuples: Vec<(u32, u32, SourceLoc)>,
 }
 
 impl DebugMap {
@@ -79,21 +80,4 @@ impl DebugMap {
 
         Ok(DebugMap { tuples })
     }
-
-    pub(crate) fn locs_from_offset<'a>(&'a self, offset: usize) -> &'a [(u32, u32, SourceLoc)] {
-        let offset = u32::try_from(offset).unwrap();
-        let start = match self.tuples.binary_search_by(|&(start, len, _)| {
-            if offset < start {
-                std::cmp::Ordering::Greater
-            } else if offset >= (start + len) {
-                std::cmp::Ordering::Less
-            } else {
-                std::cmp::Ordering::Equal
-            }
-        }) {
-            Ok(idx) => idx,
-            Err(first_after) => first_after,
-        };
-        &self.tuples[start..]
-    }
 }