Merge pull request #16852 from ziglang/issue-16751

macho: tie FDEs and unwind records to all symbol aliases, not just the first global

src/link/MachO/Object.zig

@@ -718,7 +718,7 @@ fn parseEhFrameSection(self: *Object, zld: *Zld, object_id: u32) !void {
     }
 
     try self.eh_frame_relocs_lookup.ensureTotalCapacity(gpa, record_count);
-    try self.eh_frame_records_lookup.ensureTotalCapacity(gpa, record_count);
+    try self.eh_frame_records_lookup.ensureUnusedCapacity(gpa, record_count);
 
     it.reset();
 
@@ -768,11 +768,28 @@ fn parseEhFrameSection(self: *Object, zld: *Zld, object_id: u32) !void {
                     else => unreachable,
                 }
             };
-            log.debug("FDE at offset {x} tracks {s}", .{ offset, zld.getSymbolName(target) });
             if (target.getFile() != object_id) {
+                log.debug("FDE at offset {x} marked DEAD", .{offset});
                 self.eh_frame_relocs_lookup.getPtr(offset).?.dead = true;
             } else {
-                self.eh_frame_records_lookup.putAssumeCapacityNoClobber(target, offset);
+                // You would think that we are done but turns out that the compilers may use
+                // whichever symbol alias they want for a target symbol. This in particular
+                // very problematic when using Zig's @export feature to re-export symbols under
+                // additional names. For that reason, we need to ensure we record aliases here
+                // too so that we can tie them with their matching unwind records and vice versa.
+                const aliases = self.getSymbolAliases(target.sym_index);
+                var i: u32 = 0;
+                while (i < aliases.len) : (i += 1) {
+                    const actual_target = SymbolWithLoc{
+                        .sym_index = i + aliases.start,
+                        .file = target.file,
+                    };
+                    log.debug("FDE at offset {x} tracks {s}", .{
+                        offset,
+                        zld.getSymbolName(actual_target),
+                    });
+                    try self.eh_frame_records_lookup.putNoClobber(gpa, actual_target, offset);
+                }
             }
         }
     }
@@ -803,7 +820,7 @@ fn parseUnwindInfo(self: *Object, zld: *Zld, object_id: u32) !void {
 
     const unwind_records = self.getUnwindRecords();
 
-    try self.unwind_records_lookup.ensureTotalCapacity(gpa, @as(u32, @intCast(unwind_records.len)));
+    try self.unwind_records_lookup.ensureUnusedCapacity(gpa, @as(u32, @intCast(unwind_records.len)));
 
     const needs_eh_frame = for (unwind_records) |record| {
         if (UnwindInfo.UnwindEncoding.isDwarf(record.compactUnwindEncoding, cpu_arch)) break true;
@@ -839,11 +856,28 @@ fn parseUnwindInfo(self: *Object, zld: *Zld, object_id: u32) !void {
             .code = mem.asBytes(&record),
             .base_offset = @as(i32, @intCast(offset)),
         });
-        log.debug("unwind record {d} tracks {s}", .{ record_id, zld.getSymbolName(target) });
         if (target.getFile() != object_id) {
+            log.debug("unwind record {d} marked DEAD", .{record_id});
             self.unwind_relocs_lookup[record_id].dead = true;
         } else {
-            self.unwind_records_lookup.putAssumeCapacityNoClobber(target, @as(u32, @intCast(record_id)));
+            // You would think that we are done but turns out that the compilers may use
+            // whichever symbol alias they want for a target symbol. This in particular
+            // very problematic when using Zig's @export feature to re-export symbols under
+            // additional names. For that reason, we need to ensure we record aliases here
+            // too so that we can tie them with their matching unwind records and vice versa.
+            const aliases = self.getSymbolAliases(target.sym_index);
+            var i: u32 = 0;
+            while (i < aliases.len) : (i += 1) {
+                const actual_target = SymbolWithLoc{
+                    .sym_index = i + aliases.start,
+                    .file = target.file,
+                };
+                log.debug("unwind record {d} tracks {s}", .{
+                    record_id,
+                    zld.getSymbolName(actual_target),
+                });
+                try self.unwind_records_lookup.putNoClobber(gpa, actual_target, @intCast(record_id));
+            }
         }
     }
 }
@@ -991,6 +1025,18 @@ pub fn getSymbolName(self: Object, index: u32) []const u8 {
     return strtab[start..][0 .. len - 1 :0];
 }
 
+fn getSymbolAliases(self: Object, index: u32) Entry {
+    const addr = self.source_address_lookup[index];
+    var start = index;
+    while (start > 0 and
+        self.source_address_lookup[start - 1] == addr) : (start -= 1)
+    {}
+    const end: u32 = for (self.source_address_lookup[start..], start..) |saddr, i| {
+        if (saddr != addr) break @as(u32, @intCast(i));
+    } else @as(u32, @intCast(self.source_address_lookup.len));
+    return .{ .start = start, .len = end - start };
+}
+
 pub fn getSymbolByAddress(self: Object, addr: u64, sect_hint: ?u8) u32 {
     // Find containing atom
     const Predicate = struct {
@@ -1012,11 +1058,8 @@ pub fn getSymbolByAddress(self: Object, addr: u64, sect_hint: ?u8) u32 {
             if (target_sym_index > 0) {
                 // Hone in on the most senior alias of the target symbol.
                 // See SymbolAtIndex.lessThan for more context.
-                var start = target_sym_index - 1;
-                while (start > 0 and
-                    self.source_address_lookup[lookup.start..][start - 1] == addr) : (start -= 1)
-                {}
-                return @as(u32, @intCast(lookup.start + start));
+                const aliases = self.getSymbolAliases(@intCast(lookup.start + target_sym_index - 1));
+                return aliases.start;
             }
         }
         return self.getSectionAliasSymbolIndex(sect_id);

test/link.zig

@@ -156,6 +156,10 @@ pub const cases = [_]Case{
         .build_root = "test/link/macho/pagezero",
         .import = @import("link/macho/pagezero/build.zig"),
     },
+    .{
+        .build_root = "test/link/macho/reexports",
+        .import = @import("link/macho/reexports/build.zig"),
+    },
     .{
         .build_root = "test/link/macho/search_strategy",
         .import = @import("link/macho/search_strategy/build.zig"),

test/link/macho/reexports/a.zig

@@ -0,0 +1,7 @@
+const x: i32 = 42;
+export fn foo() i32 {
+    return x;
+}
+comptime {
+    @export(foo, .{ .name = "bar", .linkage = .Strong });
+}

test/link/macho/reexports/build.zig

@@ -0,0 +1,38 @@
+const std = @import("std");
+
+pub const requires_symlinks = true;
+
+pub fn build(b: *std.Build) void {
+    const test_step = b.step("test", "Test it");
+    b.default_step = test_step;
+
+    add(b, test_step, .Debug);
+    add(b, test_step, .ReleaseFast);
+    add(b, test_step, .ReleaseSmall);
+    add(b, test_step, .ReleaseSafe);
+}
+
+fn add(b: *std.Build, test_step: *std.Build.Step, optimize: std.builtin.OptimizeMode) void {
+    const target: std.zig.CrossTarget = .{ .os_tag = .macos };
+
+    const lib = b.addStaticLibrary(.{
+        .name = "a",
+        .root_source_file = .{ .path = "a.zig" },
+        .optimize = optimize,
+        .target = target,
+    });
+
+    const exe = b.addExecutable(.{
+        .name = "test",
+        .optimize = optimize,
+        .target = target,
+    });
+    exe.addCSourceFile(.{ .file = .{ .path = "main.c" }, .flags = &.{} });
+    exe.linkLibrary(lib);
+    exe.linkLibC();
+
+    const run = b.addRunArtifact(exe);
+    run.skip_foreign_checks = true;
+    run.expectExitCode(0);
+    test_step.dependOn(&run.step);
+}

test/link/macho/reexports/main.c

@@ -0,0 +1,5 @@
+extern int foo();
+extern int bar();
+int main() {
+  return bar() - foo();
+}