Commit `897a5a4735`

Jakub Konka <kubkon@jakubkonka.com>

2022-02-23 18:42:07

macho: synthesising __mh_execute_header needs to work with incremental

Prior to this change, the routine would assume it is called first, before any symbol was created, thus precluding an option that in the incremental setting, we might have already pulled a suitably defined and exported symbol that could collide and/or be replaced by the symbol synthesised by the linker.

master

1 parent acec06c

Changed files (1)

src

link

MachO.zig

@@ -3047,6 +3047,9 @@ fn createMhExecuteHeaderAtom(self: *MachO) !void {
         .seg = self.text_segment_cmd_index.?,
         .sect = self.text_section_index.?,
     };
+    const seg = self.load_commands.items[match.seg].segment;
+    const sect = seg.sections.items[match.sect];
+
     const n_strx = try self.makeString("__mh_execute_header");
     const local_sym_index = @intCast(u32, self.locals.items.len);
     var nlist = macho.nlist_64{
@@ -3054,29 +3057,42 @@ fn createMhExecuteHeaderAtom(self: *MachO) !void {
         .n_type = macho.N_SECT,
         .n_sect = @intCast(u8, self.section_ordinals.getIndex(match).? + 1),
         .n_desc = 0,
-        .n_value = 0,
+        .n_value = sect.addr,
     };
     try self.locals.append(self.base.allocator, nlist);
+    self.mh_execute_header_index = local_sym_index;
 
-    nlist.n_type |= macho.N_EXT;
-    const global_sym_index = @intCast(u32, self.globals.items.len);
-    try self.globals.append(self.base.allocator, nlist);
-    try self.symbol_resolver.putNoClobber(self.base.allocator, n_strx, .{
-        .where = .global,
-        .where_index = global_sym_index,
-        .local_sym_index = local_sym_index,
-        .file = null,
-    });
+    if (self.symbol_resolver.getPtr(n_strx)) |resolv| {
+        const global = &self.globals.items[resolv.where_index];
+        if (!(global.weakDef() or !global.pext())) {
+            log.err("symbol '__mh_execute_header' defined multiple times", .{});
+            return error.MultipleSymbolDefinitions;
+        }
+        resolv.local_sym_index = local_sym_index;
+    } else {
+        const global_sym_index = @intCast(u32, self.globals.items.len);
+        nlist.n_type |= macho.N_EXT;
+        try self.globals.append(self.base.allocator, nlist);
+        try self.symbol_resolver.putNoClobber(self.base.allocator, n_strx, .{
+            .where = .global,
+            .where_index = global_sym_index,
+            .local_sym_index = local_sym_index,
+            .file = null,
+        });
+    }
 
+    // We always set the __mh_execute_header to point to the beginning of the __TEXT,__text section
     const atom = try self.createEmptyAtom(local_sym_index, 0, 0);
-
-    if (self.needs_prealloc) {
-        const sym = &self.locals.items[local_sym_index];
-        const vaddr = try self.allocateAtom(atom, 0, 1, match);
-        sym.n_value = vaddr;
-    } else try self.addAtomToSection(atom, match);
-
-    self.mh_execute_header_index = local_sym_index;
+    if (self.atoms.get(match)) |last| {
+        var first = last;
+        while (first.prev) |prev| {
+            first = prev;
+        }
+        atom.next = first;
+        first.prev = atom;
+    } else {
+        try self.atoms.putNoClobber(self.base.allocator, match, atom);
+    }
 }
 
 fn resolveDyldStubBinder(self: *MachO) !void {

Commit 897a5a4735

Commit `897a5a4735`