macho: update how we insert output sections

Instead of generating sections upfront, allow generation by scanning
the object files for input -> output sections mapping. Next, always
strive to keep output sections in the final container sorted as they
appear in the final binary. This makes the linker less messy wrt
handling of output sections sort order for dyld/macOS not to complain.
There's still more work to be done for incremental context though
to make this work but looks promising already.

1 files changed, 18 insertions, 5 deletions

diff --git a/src/link/MachO/Object.zig b/src/link/MachO/Object.zig
index 2e2f3dad84..996a85ed4b 100644
--- a/src/link/MachO/Object.zig
+++ b/src/link/MachO/Object.zig
@@ -214,6 +214,23 @@ fn filterRelocs(
     return relocs[start..end];
 }
 
+pub fn scanInputSections(self: Object, macho_file: *MachO) !void {
+    for (self.sections.items) |sect| {
+        const match = (try macho_file.getOutputSection(sect)) orelse {
+            log.debug("  unhandled section", .{});
+            continue;
+        };
+        const output = macho_file.sections.items(.header)[match];
+        log.debug("mapping '{s},{s}' into output sect({d}, '{s},{s}')", .{
+            sect.segName(),
+            sect.sectName(),
+            match + 1,
+            output.segName(),
+            output.sectName(),
+        });
+    }
+}
+
 /// Splits object into atoms assuming one-shot linking mode.
 pub fn splitIntoAtomsOneShot(self: *Object, macho_file: *MachO, object_id: u32) !void {
     assert(macho_file.mode == .one_shot);
@@ -280,13 +297,9 @@ pub fn splitIntoAtomsOneShot(self: *Object, macho_file: *MachO, object_id: u32)
         });
 
         const cpu_arch = macho_file.base.options.target.cpu.arch;
-        const is_zerofill = blk: {
-            const section_type = sect.type_();
-            break :blk section_type == macho.S_ZEROFILL or section_type == macho.S_THREAD_LOCAL_ZEROFILL;
-        };
 
         // Read section's code
-        const code: ?[]const u8 = if (!is_zerofill) try self.getSectionContents(sect) else null;
+        const code: ?[]const u8 = if (!sect.isZerofill()) try self.getSectionContents(sect) else null;
 
         // Read section's list of relocations
         const relocs = @ptrCast(