read/coff: add support for extended relocations (gimli-rs#399)

src/read/coff/section.rs

@@ -470,8 +470,24 @@ impl pe::ImageSectionHeader {
         &self,
         data: R,
     ) -> read::Result<&'data [pe::ImageRelocation]> {
-        let pointer = self.pointer_to_relocations.get(LE).into();
-        let number = self.number_of_relocations.get(LE).into();
+        let mut pointer = self.pointer_to_relocations.get(LE).into();
+        let mut number: usize = self.number_of_relocations.get(LE).into();
+        if number == core::u16::MAX.into()
+            && self.characteristics.get(LE) & pe::IMAGE_SCN_LNK_NRELOC_OVFL != 0
+        {
+            // Extended relocations. Read first relocation (which contains extended count) & adjust
+            // relocations pointer.
+            let extended_relocation_info = data
+                .read_at::<pe::ImageRelocation>(pointer)
+                .read_error("Invalid COFF relocation offset or number")?;
+            number = extended_relocation_info.virtual_address.get(LE) as usize;
+            if number == 0 {
+                return Err(Error("Invalid COFF relocation number"));
+            }
+            pointer += core::mem::size_of::<pe::ImageRelocation>() as u64;
+            // Extended relocation info does not contribute to the count of sections.
+            number -= 1;
+        }
         data.read_slice_at(pointer, number)
             .read_error("Invalid COFF relocation offset or number")
     }

tests/coff.rs

@@ -0,0 +1,23 @@
+use object::{pe, read, Object, ObjectSection};
+use std::fs;
+use std::path::PathBuf;
+
+#[cfg(feature = "coff")]
+#[test]
+fn coff_extended_relocations() {
+    let path_to_obj: PathBuf = ["testfiles", "coff", "relocs_overflow.o"].iter().collect();
+    let contents = fs::read(&path_to_obj).expect("Could not read relocs_overflow.o");
+    let file =
+        read::coff::CoffFile::parse(&contents[..]).expect("Could not parse relocs_overflow.o");
+    let code_section = file
+        .section_by_name(".text")
+        .expect("Could not find .text section in relocs_overflow.o");
+    match code_section.flags() {
+        object::SectionFlags::Coff { characteristics } => {
+            assert!(characteristics & pe::IMAGE_SCN_LNK_NRELOC_OVFL != 0)
+        }
+        _ => panic!("Invalid section flags flavour."),
+    };
+    let relocations = code_section.relocations().collect::<Vec<_>>();
+    assert_eq!(relocations.len(), 65536);
+}

tests/integration.rs

@@ -1 +1,2 @@
+mod coff;
 mod round_trip;