Support Aarch64Call relocations for Mach-O

Including calls with arbitrary addends
gimli-rs · Sep 30, 2022 · 6517a8b · 6517a8b
1 parent 89eec0a
commit 6517a8b
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Showing 2 changed files with 32 additions and 2 deletions.
diff --git a/src/write/macho.rs b/src/write/macho.rs
@@ -534,7 +534,7 @@ impl<'a> Object<'a> {
                 debug_assert_eq!(section_offsets[index].reloc_offset, buffer.len());
                 for reloc in &section.relocations {
                     let r_extern;
-                    let r_symbolnum;
+                    let mut r_symbolnum;
                     let symbol = &self.symbols[reloc.symbol.0];
                     if symbol.kind == SymbolKind::Section {
                         r_symbolnum = section_offsets[symbol.section.id().unwrap().0].index as u32;
@@ -546,7 +546,7 @@ impl<'a> Object<'a> {
                     let r_length = match reloc.size {
                         8 => 0,
                         16 => 1,
-                        32 => 2,
+                        12 | 21 | 26 | 32 => 2,
                         64 => 3,
                         _ => return Err(Error(format!("unimplemented reloc size {:?}", reloc))),
                     };
@@ -590,6 +590,28 @@ impl<'a> Object<'a> {
                             (RelocationKind::Absolute, RelocationEncoding::Generic, 0) => {
                                 (false, macho::ARM64_RELOC_UNSIGNED)
                             }
+                            // Due to the fixup an addend of -4 here means the original addend was 0
+                            (RelocationKind::Relative, RelocationEncoding::AArch64Call, -4) => {
+                                (true, macho::ARM64_RELOC_BRANCH26)
+                            }
+                            // Non-zero addend, so we have to encode the addend separately
+                            (RelocationKind::Relative, RelocationEncoding::AArch64Call, value) => {
+                                // first emit the BR26 relocation
+                                let reloc_info = macho::RelocationInfo {
+                                    r_address: reloc.offset as u32,
+                                    r_symbolnum,
+                                    r_pcrel: true,
+                                    r_length,
+                                    r_extern: true,
+                                    r_type: macho::ARM64_RELOC_BRANCH26,
+                                };
+                                buffer.write(&reloc_info.relocation(endian));
+
+                                // set up a separate relocation for the addend
+                                // we add 4 to undo the fixup of -4
+                                r_symbolnum = (value + 4) as u32;
+                                (false, macho::ARM64_RELOC_ADDEND)
+                            }
                             (
                                 RelocationKind::MachO { value, relative },
                                 RelocationEncoding::Generic,

diff --git a/src/write/mod.rs b/src/write/mod.rs
@@ -526,6 +526,14 @@ impl<'a> Object<'a> {
         match relocation.size {
             32 => data.write_at(offset, &U32::new(self.endian, addend as u32)),
             64 => data.write_at(offset, &U64::new(self.endian, addend as u64)),
+
+            // For aarch64 call relocations in Mach-O, the addend is
+            // encoded in a separate relocation, so don't write it here
+            26 if relocation.encoding == RelocationEncoding::AArch64Call
+                && self.format == BinaryFormat::MachO =>
+            {
+                Ok(())
+            }
             _ => {
                 return Err(Error(format!(
                     "unimplemented relocation addend {:?}",