[Mach-O] Handle $ld$add$ symbols

macho/tapi.cc

@@ -145,6 +145,17 @@ static void interpret_ld_symbols(Context<E> &ctx, TextDylib &tbd) {
           ctx.arg.platform_min_version < max_version) {
         tbd.install_name = save_string(ctx, install_name);
       }
+      continue;
+    }
+
+    // $ld$add$os_version$symbol adds a symbol if the given OS version
+    // matches.
+    static std::regex re_add(R"(\$ld\$add\$os([\d.]+)\$(.+))", flags);
+
+    if (std::regex_match(name, m, re_add)) {
+      if (ctx.arg.platform_min_version == parse_version(m[1]))
+        tbd.exports.push_back(save_string(ctx, m[2]));
+      continue;
     }
   }
 

test/macho/tbd-add.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+export LC_ALL=C
+set -e
+CC="${TEST_CC:-cc}"
+CXX="${TEST_CXX:-c++}"
+GCC="${TEST_GCC:-gcc}"
+GXX="${TEST_GXX:-g++}"
+OBJDUMP="${OBJDUMP:-objdump}"
+MACHINE="${MACHINE:-$(uname -m)}"
+testname=$(basename "$0" .sh)
+echo -n "Testing $testname ... "
+cd "$(dirname "$0")"/../..
+t=out/test/macho/$testname
+mkdir -p $t
+
+cat > $t/libfoo.tbd <<'EOF'
+--- !tapi-tbd
+tbd-version:     4
+targets:         [ x86_64-macos, arm64-macos ]
+uuids:
+  - target:          x86_64-macos
+    value:           00000000-0000-0000-0000-000000000000
+  - target:          arm64-macos
+    value:           00000000-0000-0000-0000-000000000000
+install-name:    '/foo'
+current-version: 0
+compatibility-version: 0
+exports:
+  - targets:         [ x86_64-macos, arm64-macos ]
+    symbols:         [ '$ld$add$os14.0$_foo' ]
+...
+EOF
+
+cat <<EOF | clang -o $t/a.o -c -xc -
+void foo();
+void bar() { foo(); }
+EOF
+
+! clang --ld-path=./ld64 -shared -o $t/b.dylib $t/libfoo.tbd $t/a.o \
+  -Wl,-platform_version,macos,9.0,9.0 >& /dev/null || false
+
+clang --ld-path=./ld64 -shared -o $t/b.dylib $t/libfoo.tbd $t/a.o \
+  -Wl,-platform_version,macos,14.0,13.0 >& /dev/null
+
+echo OK