x86_64: add support for pie executables

Author: jacobly0

CMakeLists.txt

@@ -519,6 +519,7 @@ set(ZIG_STAGE2_SOURCES
     src/Air/Legalize.zig
     src/Air/Liveness.zig
     src/Air/Liveness/Verify.zig
+    src/Air/print.zig
     src/Air/types_resolved.zig
     src/Builtin.zig
     src/Compilation.zig
@@ -675,7 +676,6 @@ set(ZIG_STAGE2_SOURCES
     src/libs/mingw.zig
     src/libs/musl.zig
     src/mutable_value.zig
-    src/print_air.zig
     src/print_env.zig
     src/print_targets.zig
     src/print_value.zig

lib/std/builtin.zig

@@ -61,7 +61,7 @@ pub const StackTrace = struct {
 
 /// This data structure is used by the Zig language code generation and
 /// therefore must be kept in sync with the compiler implementation.
-pub const GlobalLinkage = enum {
+pub const GlobalLinkage = enum(u2) {
     internal,
     strong,
     weak,
@@ -70,7 +70,7 @@ pub const GlobalLinkage = enum {
 
 /// This data structure is used by the Zig language code generation and
 /// therefore must be kept in sync with the compiler implementation.
-pub const SymbolVisibility = enum {
+pub const SymbolVisibility = enum(u2) {
     default,
     hidden,
     protected,
@@ -1030,8 +1030,19 @@ pub const ExternOptions = struct {
     name: []const u8,
     library_name: ?[]const u8 = null,
     linkage: GlobalLinkage = .strong,
+    visibility: SymbolVisibility = .default,
+    /// Setting this to `true` makes the `@extern` a runtime value.
     is_thread_local: bool = false,
     is_dll_import: bool = false,
+    relocation: Relocation = .any,
+
+    pub const Relocation = enum(u1) {
+        /// Any type of relocation is allowed.
+        any,
+        /// A program-counter-relative relocation is required.
+        /// Using this value makes the `@extern` a runtime value.
+        pcrel,
+    };
 };
 
 /// This data structure is used by the Zig language code generation and

lib/std/dynamic_library.zig

@@ -83,13 +83,16 @@ const RDebug = extern struct {
     r_ldbase: usize,
 };
 
-/// TODO make it possible to reference this same external symbol 2x so we don't need this
-/// helper function.
-pub fn get_DYNAMIC() ?[*]elf.Dyn {
-    return @extern([*]elf.Dyn, .{ .name = "_DYNAMIC", .linkage = .weak });
+/// TODO fix comparisons of extern symbol pointers so we don't need this helper function.
+pub fn get_DYNAMIC() ?[*]const elf.Dyn {
+    return @extern([*]const elf.Dyn, .{
+        .name = "_DYNAMIC",
+        .linkage = .weak,
+        .visibility = .hidden,
+    });
 }
 
-pub fn linkmap_iterator(phdrs: []elf.Phdr) error{InvalidExe}!LinkMap.Iterator {
+pub fn linkmap_iterator(phdrs: []const elf.Phdr) error{InvalidExe}!LinkMap.Iterator {
     _ = phdrs;
     const _DYNAMIC = get_DYNAMIC() orelse {
         // No PT_DYNAMIC means this is either a statically-linked program or a