Commit `e229202cb8`

Jakub Konka <kubkon@jakubkonka.com>

2021-09-07 23:21:08

macho: store source section address of relocs in context

This is particularly relevant for x86_64 and C++ when relocating StaticInit sections containing static initializers machine code. Then, in case of SIGNED_X relocations, it is necessary to have the full image of the VM address layout of the sections in the object file as this is how the addend needs to be adjusted for non-extern relocations.

master

1 parent 159e55d

Changed files (2)

src

link

MachO

Object.zig

TextBlock.zig

@@ -425,7 +425,8 @@ const TextBlockParser = struct {
         }
 
         try block.parseRelocs(self.relocs, .{
-            .base_addr = start_addr,
+            .base_addr = self.section.addr,
+            .base_offset = start_addr,
             .allocator = context.allocator,
             .object = context.object,
             .macho_file = context.macho_file,
@@ -583,7 +584,8 @@ pub fn parseTextBlocks(
                     }
 
                     try block.parseRelocs(relocs, .{
-                        .base_addr = 0,
+                        .base_addr = sect.addr,
+                        .base_offset = 0,
                         .allocator = allocator,
                         .object = self,
                         .macho_file = macho_file,
@@ -689,7 +691,8 @@ pub fn parseTextBlocks(
             }
 
             try block.parseRelocs(relocs, .{
-                .base_addr = 0,
+                .base_addr = sect.addr,
+                .base_offset = 0,
                 .allocator = allocator,
                 .object = self,
                 .macho_file = macho_file,

@@ -479,13 +479,13 @@ pub const Relocation = struct {
 
     pub const Signed = struct {
         addend: i64,
-        correction: i4,
+        correction: u3,
 
         pub fn resolve(self: Signed, args: ResolveArgs) !void {
             const target_addr = @intCast(i64, args.target_addr) + self.addend;
             const displacement = try math.cast(
                 i32,
-                target_addr - @intCast(i64, args.source_addr) - self.correction - 4,
+                target_addr - @intCast(i64, args.source_addr + self.correction + 4),
             );
             mem.writeIntLittle(u32, args.block.code.items[args.offset..][0..4], @bitCast(u32, displacement));
         }
@@ -613,6 +613,7 @@ pub fn freeListEligible(self: TextBlock, macho_file: MachO) bool {
 
 const RelocContext = struct {
     base_addr: u64 = 0,
+    base_offset: u64 = 0,
     allocator: *Allocator,
     object: *Object,
     macho_file: *MachO,
@@ -620,7 +621,7 @@ const RelocContext = struct {
 
 fn initRelocFromObject(rel: macho.relocation_info, context: RelocContext) !Relocation {
     var parsed_rel = Relocation{
-        .offset = @intCast(u32, @intCast(u64, rel.r_address) - context.base_addr),
+        .offset = @intCast(u32, @intCast(u64, rel.r_address) - context.base_offset),
         .where = undefined,
         .where_index = undefined,
         .payload = undefined,
@@ -684,7 +685,7 @@ fn initRelocFromObject(rel: macho.relocation_info, context: RelocContext) !Reloc
 }
 
 pub fn parseRelocs(self: *TextBlock, relocs: []macho.relocation_info, context: RelocContext) !void {
-    const filtered_relocs = filterRelocs(relocs, context.base_addr, context.base_addr + self.size);
+    const filtered_relocs = filterRelocs(relocs, context.base_offset, context.base_offset + self.size);
     var it = RelocIterator{
         .buffer = filtered_relocs,
     };
@@ -956,9 +957,9 @@ fn parseUnsigned(
         mem.readIntLittle(i32, self.code.items[out.offset..][0..4]);
 
     if (rel.r_extern == 0) {
-        const source_seg = context.object.load_commands.items[context.object.segment_cmd_index.?].Segment;
-        const source_sect_base_addr = source_seg.sections.items[rel.r_symbolnum - 1].addr;
-        addend -= @intCast(i64, source_sect_base_addr);
+        const seg = context.object.load_commands.items[context.object.segment_cmd_index.?].Segment;
+        const target_sect_base_addr = seg.sections.items[rel.r_symbolnum - 1].addr;
+        addend -= @intCast(i64, target_sect_base_addr);
     }
 
     out.payload = .{
@@ -1043,7 +1044,7 @@ fn parseSigned(self: TextBlock, rel: macho.relocation_info, out: *Relocation, co
     assert(rel.r_length == 2);
 
     const rel_type = @intToEnum(macho.reloc_type_x86_64, rel.r_type);
-    const correction: i4 = switch (rel_type) {
+    const correction: u3 = switch (rel_type) {
         .X86_64_RELOC_SIGNED => 0,
         .X86_64_RELOC_SIGNED_1 => 1,
         .X86_64_RELOC_SIGNED_2 => 2,
@@ -1053,9 +1054,9 @@ fn parseSigned(self: TextBlock, rel: macho.relocation_info, out: *Relocation, co
     var addend: i64 = mem.readIntLittle(i32, self.code.items[out.offset..][0..4]) + correction;
 
     if (rel.r_extern == 0) {
-        const source_seg = context.object.load_commands.items[context.object.segment_cmd_index.?].Segment;
-        const source_sect_base_addr = source_seg.sections.items[rel.r_symbolnum - 1].addr;
-        addend = @intCast(i64, out.offset) + addend - @intCast(i64, source_sect_base_addr) + 4 + correction;
+        const seg = context.object.load_commands.items[context.object.segment_cmd_index.?].Segment;
+        const target_sect_base_addr = seg.sections.items[rel.r_symbolnum - 1].addr;
+        addend += @intCast(i64, context.base_addr + out.offset + correction + 4) - @intCast(i64, target_sect_base_addr);
     }
 
     out.payload = .{

Commit e229202cb8

Commit `e229202cb8`