GCC: Fix "Instruction count mismatch" when combining text sections (#397)

Author: LagoLunatic

objdiff-core/src/arch/ppc/mod.rs

@@ -364,10 +364,10 @@ impl Arch for ArchPpc {
         bytes: &[u8],
     ) -> Option<DataType> {
         if reloc.is_some_and(|r| {
-            r.symbol.name.starts_with("@stringBase")
-                || r.symbol.name.starts_with("@wstringBase")
+            r.symbol.name.starts_with("@stringBase") // MWCC
+                || r.symbol.name.starts_with("@wstringBase") // MWCC
                 || r.symbol.name.starts_with("$SG")
-                || r.symbol.demangled_name == Some("`string'".to_string())
+                || r.symbol.name.starts_with("??_C") // MSVC
         }) {
             // Compiler-generated symbol name for a string or a pool of strings.
             return Some(DataType::String);

objdiff-core/src/diff/mod.rs

@@ -18,7 +18,7 @@ use crate::{
     },
     obj::{
         InstructionRef, Object, Relocation, ResolvedRelocation, SectionKind, Symbol, SymbolFlag,
-        SymbolKind,
+        SymbolKind, read::get_section_base_name,
     },
 };
 
@@ -810,10 +810,8 @@ where
 
 fn symbol_section<'obj>(obj: &'obj Object, symbol: &Symbol) -> Option<(&'obj str, SectionKind)> {
     if let Some(section) = symbol.section.and_then(|section_idx| obj.sections.get(section_idx)) {
-        // Match x86 .rdata$r against .rdata$rs
-        let section_name =
-            section.name.split_once('$').map_or(section.name.as_str(), |(prefix, _)| prefix);
-        Some((section_name, section.kind))
+        let section_base_name = get_section_base_name(section);
+        Some((section_base_name, section.kind))
     } else if symbol.flags.contains(SymbolFlag::Common) {
         Some((".comm", SectionKind::Common))
     } else {

objdiff-core/src/obj/read.rs

@@ -89,15 +89,17 @@ fn get_normalized_symbol_name(name: &str) -> Option<String> {
     }
 }
 
-/// Check if a symbol's name is entirely compiler-generated, such as @1234 or _$E1234.
+/// Check if a symbol's name is entirely compiler-generated (e.g. for a literal).
 /// This enables pairing these symbols up by their value instead of their name.
 fn is_symbol_name_compiler_generated(name: &str) -> bool {
     if name.starts_with('@') && name[1..].chars().all(char::is_numeric) {
-        // Exclude @stringBase0, @GUARD@, etc.
+        // Match Metrowerks @1234 against @2345
         return true;
-    } else if (name.starts_with("_$E") || name.starts_with("$LC"))
-        && name[3..].chars().all(char::is_numeric)
-    {
+    } else if name.starts_with("_$E") && name[3..].chars().all(char::is_numeric) {
+        // Match MSVC _$E1234 against _$E2345
+        return true;
+    } else if name.starts_with("$LC") && name[3..].chars().all(char::is_numeric) {
+        // Match GCC $LC1234 against $LC2345
         return true;
     }
     false
@@ -926,6 +928,17 @@ fn parse_line_info_coff(
     Ok(())
 }
 
+pub fn get_section_base_name(section: &Section) -> &str {
+    // Match MSVC x86 .rdata$r against .rdata$rs
+    // Match GCC i._ZN14class_00acb578C1Ev against i [combined]
+    section
+        .name
+        .get(1..)
+        .and_then(|s| s.rfind(['$', '.']))
+        .and_then(|i| section.name.get(..i + 1))
+        .unwrap_or(&section.name)
+}
+
 fn combine_sections(
     sections: &mut [Section],
     symbols: &mut [Symbol],
@@ -934,12 +947,7 @@ fn combine_sections(
     let mut data_sections = BTreeMap::<String, Vec<usize>>::new();
     let mut text_sections = BTreeMap::<String, Vec<usize>>::new();
     for (i, section) in sections.iter().enumerate() {
-        let base_name = section
-            .name
-            .get(1..)
-            .and_then(|s| s.rfind(['$', '.']))
-            .and_then(|i| section.name.get(..i + 1))
-            .unwrap_or(&section.name);
+        let base_name = get_section_base_name(section);
         match section.kind {
             SectionKind::Data | SectionKind::Bss => {
                 data_sections.entry(base_name.to_string()).or_default().push(i);