Match original "exec" for REL sections

mwld writes empty code sections as
NULL type in the PLF, but sometimes
the original REL has the exec flag
set for these sections. Match the
original value.

src/cmd/rel.rs

@@ -346,8 +346,11 @@ fn make(args: MakeArgs) -> Result<()> {
             section_count: None,
             quiet: args.no_warn,
             section_align: None,
+            section_exec: None,
         };
-        if let Some((header, _, section_defs)) = existing_headers.get(&(module_id as u32)) {
+        if let Some((header, section_headers, section_defs)) =
+            existing_headers.get(&(module_id as u32))
+        {
             info.version = header.version;
             info.name_offset = Some(header.name_offset);
             info.name_size = Some(header.name_size);
@@ -358,6 +361,7 @@ fn make(args: MakeArgs) -> Result<()> {
                 .as_ref()
                 .map(|defs| defs.iter().map(|def| def.align).collect())
                 .unwrap_or_default();
+            info.section_exec = Some(section_headers.iter().map(|s| s.exec()).collect());
         }
         let rel_path = path.with_extension("rel");
         let mut w = buf_writer(&rel_path)?;

src/util/rel.rs

@@ -688,6 +688,10 @@ pub struct RelWriteInfo {
     pub quiet: bool,
     /// Override individual section alignment in the file.
     pub section_align: Option<Vec<u32>>,
+    /// Override individual section executable status in the file.
+    /// This is used to match empty sections: mwld will emit them with
+    /// NULL type, but the original REL may have them marked executable.
+    pub section_exec: Option<Vec<bool>>,
 }
 
 pub const PERMITTED_SECTIONS: [&str; 7] =
@@ -1006,12 +1010,12 @@ where
                 offset = current_data_offset;
                 current_data_offset += section.size() as u32;
             }
-            RelSectionHeader::new(
-                offset,
-                section.size() as u32,
-                section.kind() == object::SectionKind::Text,
-            )
-            .to_writer(w, Endian::Big)?;
+            let exec = info
+                .section_exec
+                .as_ref()
+                .and_then(|m| m.get(section_index as usize).copied())
+                .unwrap_or(section.kind() == object::SectionKind::Text);
+            RelSectionHeader::new(offset, section.size() as u32, exec).to_writer(w, Endian::Big)?;
             permitted_section_idx += 1;
         } else {
             RelSectionHeader::new(0, 0, false).to_writer(w, Endian::Big)?;