From 9c4c6b806806867f46d4a8e7e5f7673e010ddc23 Mon Sep 17 00:00:00 2001
From: Thomas Lamb <tclamb@fla-inc.com>
Date: Mon, 19 Oct 2026 01:16:39 -0400
Subject: [PATCH] Fix MIPS NON_MATCHING symbols when undefined symbol shadows
 ignored name

When a base object contains an undefined symbol with the same name as a
NON_MATCHING-marked function, object.symbol_by_name could return that
undefined symbol instead of the defined function. This left the placeholder
unignored and erroneously reported as matched.
---
 objdiff-core/src/arch/mips.rs                 |  11 +++++---
 objdiff-core/tests/arch_mips.rs               |  26 ++++++++++++++++++
 .../tests/data/mips/non_matching_undef.o      | Bin 0 -> 936 bytes
 3 files changed, 33 insertions(+), 4 deletions(-)
 create mode 100644 objdiff-core/tests/data/mips/non_matching_undef.o

diff --git a/objdiff-core/src/arch/mips.rs b/objdiff-core/src/arch/mips.rs
index 72687d9f..98d7fa81 100644
--- a/objdiff-core/src/arch/mips.rs
+++ b/objdiff-core/src/arch/mips.rs
@@ -130,10 +130,13 @@ impl ArchMips {
                 ignored_symbols.insert(obj_symbol.index().0);
                 // Only remove the prefixless symbols if we are on the Base side of the diff,
                 // to allow diffing against target objects that contain `.NON_MATCHING` markers.
-                if diff_side == DiffSide::Base
-                    && let Some(target_symbol) = object.symbol_by_name(prefix)
-                {
-                    ignored_symbols.insert(target_symbol.index().0);
+                if diff_side == DiffSide::Base {
+                    for candidate in object.symbols() {
+                        let Ok(candidate_name) = candidate.name() else { continue };
+                        if candidate_name == prefix {
+                            ignored_symbols.insert(candidate.index().0);
+                        }
+                    }
                 }
             }
         }
diff --git a/objdiff-core/tests/arch_mips.rs b/objdiff-core/tests/arch_mips.rs
index 79ae0083..a81d4ae5 100644
--- a/objdiff-core/tests/arch_mips.rs
+++ b/objdiff-core/tests/arch_mips.rs
@@ -127,3 +127,29 @@ fn ee_gcc_mdebug_line_numbers() {
     assert_eq!(text_section.line_info.get(&144), Some(&13));
     assert_eq!(text_section.line_info.len(), 10);
 }
+
+#[test]
+#[cfg(feature = "mips")]
+fn filter_non_matching_with_undef_symbol() {
+    let diff_config = diff::DiffObjConfig::default();
+    let obj = obj::read::parse(
+        include_object!("data/mips/non_matching_undef.o"),
+        &diff_config,
+        diff::DiffSide::Base,
+    )
+    .unwrap();
+
+    let defined_foo = obj
+        .symbols
+        .iter()
+        .find(|s| s.name == "foo" && s.section.is_some())
+        .expect("defined foo symbol present");
+    assert!(
+        defined_foo.flags.contains(obj::SymbolFlag::Ignored),
+        "defined foo symbol should be ignored when a same-named undefined symbol exists"
+    );
+
+    let marker =
+        obj.symbols.iter().find(|s| s.name == "foo.NON_MATCHING").expect("marker symbol present");
+    assert!(marker.flags.contains(obj::SymbolFlag::Ignored));
+}
diff --git a/objdiff-core/tests/data/mips/non_matching_undef.o b/objdiff-core/tests/data/mips/non_matching_undef.o
new file mode 100644
index 0000000000000000000000000000000000000000..351e7f52ceea52bdbdafbfe1824be314758039e4
GIT binary patch
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