Merge pull request #22035 from alexrp/unwind-fixes

Better unwind table support + unwind protection in `_start()` and `clone()`

12 files changed, 144 insertions, 42 deletions

diff --git a/src/Builtin.zig b/src/Builtin.zig
index 8dc5b31c16..1782527f69 100644
--- a/src/Builtin.zig
+++ b/src/Builtin.zig
@@ -2,6 +2,7 @@ target: std.Target,
 zig_backend: std.builtin.CompilerBackend,
 output_mode: std.builtin.OutputMode,
 link_mode: std.builtin.LinkMode,
+unwind_tables: std.builtin.UnwindTables,
 is_test: bool,
 single_threaded: bool,
 link_libc: bool,
@@ -40,6 +41,7 @@ pub fn append(opts: @This(), buffer: *std.ArrayList(u8)) Allocator.Error!void {
         \\
         \\pub const output_mode: std.builtin.OutputMode = .{p_};
         \\pub const link_mode: std.builtin.LinkMode = .{p_};
+        \\pub const unwind_tables: std.builtin.UnwindTables = .{p_};
         \\pub const is_test = {};
         \\pub const single_threaded = {};
         \\pub const abi: std.Target.Abi = .{p_};
@@ -53,6 +55,7 @@ pub fn append(opts: @This(), buffer: *std.ArrayList(u8)) Allocator.Error!void {
         std.zig.fmtId(@tagName(zig_backend)),
         std.zig.fmtId(@tagName(opts.output_mode)),
         std.zig.fmtId(@tagName(opts.link_mode)),
+        std.zig.fmtId(@tagName(opts.unwind_tables)),
         opts.is_test,
         opts.single_threaded,
         std.zig.fmtId(@tagName(target.abi)),
diff --git a/src/Compilation.zig b/src/Compilation.zig
index 5f4404ff99..947012e716 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -1261,12 +1261,15 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
         // The "any" values provided by resolved config only account for
         // explicitly-provided settings. We now make them additionally account
         // for default setting resolution.
-        const any_unwind_tables = options.config.any_unwind_tables or options.root_mod.unwind_tables;
+        const any_unwind_tables = switch (options.config.any_unwind_tables) {
+            .none => options.root_mod.unwind_tables,
+            .sync, .@"async" => |uwt| uwt,
+        };
         const any_non_single_threaded = options.config.any_non_single_threaded or !options.root_mod.single_threaded;
         const any_sanitize_thread = options.config.any_sanitize_thread or options.root_mod.sanitize_thread;
         const any_fuzz = options.config.any_fuzz or options.root_mod.fuzz;
 
-        const link_eh_frame_hdr = options.link_eh_frame_hdr or any_unwind_tables;
+        const link_eh_frame_hdr = options.link_eh_frame_hdr or any_unwind_tables != .none;
         const build_id = options.build_id orelse .none;
 
         const link_libc = options.config.link_libc;
@@ -1354,6 +1357,7 @@ pub fn create(gpa: Allocator, arena: Allocator, options: CreateOptions) !*Compil
         cache.hash.add(options.config.pie);
         cache.hash.add(options.config.lto);
         cache.hash.add(options.config.link_mode);
+        cache.hash.add(options.config.any_unwind_tables);
         cache.hash.add(options.function_sections);
         cache.hash.add(options.data_sections);
         cache.hash.add(link_libc);
@@ -5553,10 +5557,17 @@ pub fn addCCArgs(
                 try argv.append("-Werror=date-time");
             }
 
-            if (mod.unwind_tables) {
-                try argv.append("-funwind-tables");
-            } else {
-                try argv.append("-fno-unwind-tables");
+            switch (mod.unwind_tables) {
+                .none => {
+                    try argv.append("-fno-unwind-tables");
+                    try argv.append("-fno-asynchronous-unwind-tables");
+                },
+                .sync => {
+                    // Need to override Clang's convoluted default logic.
+                    try argv.append("-fno-asynchronous-unwind-tables");
+                    try argv.append("-funwind-tables");
+                },
+                .@"async" => try argv.append("-fasynchronous-unwind-tables"),
             }
         },
         .shared_library, .ll, .bc, .unknown, .static_library, .object, .def, .zig, .res, .manifest => {},
@@ -6288,6 +6299,7 @@ pub const CrtFileOptions = struct {
     function_sections: ?bool = null,
     data_sections: ?bool = null,
     omit_frame_pointer: ?bool = null,
+    unwind_tables: ?std.builtin.UnwindTables = null,
     pic: ?bool = null,
     no_builtin: ?bool = null,
 };
@@ -6349,7 +6361,8 @@ pub fn build_crt_file(
             // Some libcs (e.g. musl) are opinionated about -fomit-frame-pointer.
             .omit_frame_pointer = options.omit_frame_pointer orelse comp.root_mod.omit_frame_pointer,
             .valgrind = false,
-            .unwind_tables = false,
+            // Some libcs (e.g. MinGW) are opinionated about -funwind-tables.
+            .unwind_tables = options.unwind_tables orelse .none,
             // Some CRT objects (e.g. musl's rcrt1.o and Scrt1.o) are opinionated about PIC.
             .pic = options.pic orelse comp.root_mod.pic,
             .optimize_mode = comp.compilerRtOptMode(),
diff --git a/src/Compilation/Config.zig b/src/Compilation/Config.zig
index 4458d474bb..baaa6c9f47 100644
--- a/src/Compilation/Config.zig
+++ b/src/Compilation/Config.zig
@@ -12,13 +12,14 @@ link_libunwind: bool,
 /// True if and only if the c_source_files field will have nonzero length when
 /// calling Compilation.create.
 any_c_source_files: bool,
-/// This is true if any Module has unwind_tables set explicitly to true. Until
-/// Compilation.create is called, it is possible for this to be false while in
-/// fact all Module instances have unwind_tables=true due to the default
-/// being unwind_tables=true. After Compilation.create is called this will
-/// also take into account the default setting, making this value true if and
-/// only if any Module has unwind_tables set to true.
-any_unwind_tables: bool,
+/// This is not `.none` if any `Module` has `unwind_tables` set explicitly to a
+/// value other than `.none`. Until `Compilation.create()` is called, it is
+/// possible for this to be `.none` while in fact all `Module` instances have
+/// `unwind_tables != .none` due to the default. After `Compilation.create()` is
+/// called, this will also take into account the default setting, making this
+/// value `.sync` or `.@"async"` if and only if any `Module` has
+/// `unwind_tables != .none`.
+any_unwind_tables: std.builtin.UnwindTables,
 /// This is true if any Module has single_threaded set explicitly to false. Until
 /// Compilation.create is called, it is possible for this to be false while in
 /// fact all Module instances have single_threaded=false due to the default
@@ -85,7 +86,7 @@ pub const Options = struct {
     any_non_single_threaded: bool = false,
     any_sanitize_thread: bool = false,
     any_fuzz: bool = false,
-    any_unwind_tables: bool = false,
+    any_unwind_tables: std.builtin.UnwindTables = .none,
     any_dyn_libs: bool = false,
     any_c_source_files: bool = false,
     any_non_stripped: bool = false,
@@ -356,8 +357,11 @@ pub fn resolve(options: Options) ResolveError!Config {
         break :b false;
     };
 
-    const any_unwind_tables = options.any_unwind_tables or
-        link_libunwind or target_util.needUnwindTables(target);
+    const any_unwind_tables = b: {
+        if (options.any_unwind_tables != .none) break :b options.any_unwind_tables;
+
+        break :b target_util.needUnwindTables(target, link_libunwind, options.any_sanitize_thread);
+    };
 
     const link_mode = b: {
         const explicitly_exe_or_dyn_lib = switch (options.output_mode) {
diff --git a/src/Package/Module.zig b/src/Package/Module.zig
index 781a8e50c2..bfcef038ed 100644
--- a/src/Package/Module.zig
+++ b/src/Package/Module.zig
@@ -27,7 +27,7 @@ red_zone: bool,
 sanitize_c: bool,
 sanitize_thread: bool,
 fuzz: bool,
-unwind_tables: bool,
+unwind_tables: std.builtin.UnwindTables,
 cc_argv: []const []const u8,
 /// (SPIR-V) whether to generate a structured control flow graph or not
 structured_cfg: bool,
@@ -91,7 +91,7 @@ pub const CreateOptions = struct {
         /// other number means stack protection with that buffer size.
         stack_protector: ?u32 = null,
         red_zone: ?bool = null,
-        unwind_tables: ?bool = null,
+        unwind_tables: ?std.builtin.UnwindTables = null,
         sanitize_c: ?bool = null,
         sanitize_thread: ?bool = null,
         fuzz: ?bool = null,
@@ -112,7 +112,7 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
     if (options.inherited.sanitize_thread == true) assert(options.global.any_sanitize_thread);
     if (options.inherited.fuzz == true) assert(options.global.any_fuzz);
     if (options.inherited.single_threaded == false) assert(options.global.any_non_single_threaded);
-    if (options.inherited.unwind_tables == true) assert(options.global.any_unwind_tables);
+    if (options.inherited.unwind_tables) |uwt| if (uwt != .none) assert(options.global.any_unwind_tables != .none);
     if (options.inherited.error_tracing == true) assert(options.global.any_error_tracing);
 
     const resolved_target = options.inherited.resolved_target orelse options.parent.?.resolved_target;
@@ -382,6 +382,7 @@ pub fn create(arena: Allocator, options: CreateOptions) !*Package.Module {
             .zig_backend = zig_backend,
             .output_mode = options.global.output_mode,
             .link_mode = options.global.link_mode,
+            .unwind_tables = options.global.any_unwind_tables,
             .is_test = options.global.is_test,
             .single_threaded = single_threaded,
             .link_libc = options.global.link_libc,
diff --git a/src/arch/riscv64/CodeGen.zig b/src/arch/riscv64/CodeGen.zig
index 29a0a8b8b5..a836d02d71 100644
--- a/src/arch/riscv64/CodeGen.zig
+++ b/src/arch/riscv64/CodeGen.zig
@@ -8442,6 +8442,10 @@ fn failSymbol(func: *Func, comptime format: []const u8, args: anytype) InnerErro
 }
 
 fn parseRegName(name: []const u8) ?Register {
+    // The `fp` alias for `s0` is awkward to fit into the current `Register` scheme, so for now we
+    // special-case it here.
+    if (std.mem.eql(u8, name, "fp")) return .s0;
+
     return std.meta.stringToEnum(Register, name);
 }
 
diff --git a/src/clang_options_data.zig b/src/clang_options_data.zig
index 9ced7e9ebe..88cf41d0d4 100644
--- a/src/clang_options_data.zig
+++ b/src/clang_options_data.zig
@@ -2757,7 +2757,14 @@ flagpd1("fast"),
 flagpd1("fastcp"),
 flagpd1("fastf"),
 flagpd1("fasync-exceptions"),
-flagpd1("fasynchronous-unwind-tables"),
+.{
+    .name = "fasynchronous-unwind-tables",
+    .syntax = .flag,
+    .zig_equivalent = .asynchronous_unwind_tables,
+    .pd1 = true,
+    .pd2 = false,
+    .psl = false,
+},
 flagpd1("fauto-import"),
 flagpd1("fauto-profile"),
 flagpd1("fauto-profile-accurate"),
@@ -3247,7 +3254,14 @@ flagpd1("fno-assume-sane-operator-new"),
 flagpd1("fno-assume-unique-vtables"),
 flagpd1("fno-assumptions"),
 flagpd1("fno-async-exceptions"),
-flagpd1("fno-asynchronous-unwind-tables"),
+.{
+    .name = "fno-asynchronous-unwind-tables",
+    .syntax = .flag,
+    .zig_equivalent = .no_asynchronous_unwind_tables,
+    .pd1 = true,
+    .pd2 = false,
+    .psl = false,
+},
 flagpd1("fno-auto-import"),
 flagpd1("fno-auto-profile"),
 flagpd1("fno-auto-profile-accurate"),
diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index ff1e679898..b94ea07995 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -3141,8 +3141,11 @@ pub const Object = struct {
             } }, &o.builder);
         }
         try attributes.addFnAttr(.nounwind, &o.builder);
-        if (owner_mod.unwind_tables) {
-            try attributes.addFnAttr(.{ .uwtable = Builder.Attribute.UwTable.default }, &o.builder);
+        if (owner_mod.unwind_tables != .none) {
+            try attributes.addFnAttr(
+                .{ .uwtable = if (owner_mod.unwind_tables == .@"async") .@"async" else .sync },
+                &o.builder,
+            );
         }
         if (owner_mod.no_builtin) {
             // The intent here is for compiler-rt and libc functions to not generate
diff --git a/src/libcxx.zig b/src/libcxx.zig
index 39fd999112..6386d493a6 100644
--- a/src/libcxx.zig
+++ b/src/libcxx.zig
@@ -397,7 +397,6 @@ pub fn buildLibCXXABI(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
 
     const optimize_mode = comp.compilerRtOptMode();
     const strip = comp.compilerRtStrip();
-    const unwind_tables = true;
 
     const config = Compilation.Config.resolve(.{
         .output_mode = output_mode,
@@ -409,7 +408,6 @@ pub fn buildLibCXXABI(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
         .root_optimize_mode = optimize_mode,
         .root_strip = strip,
         .link_libc = true,
-        .any_unwind_tables = unwind_tables,
         .lto = comp.config.lto,
         .any_sanitize_thread = comp.config.any_sanitize_thread,
     }) catch |err| {
@@ -440,7 +438,12 @@ pub fn buildLibCXXABI(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
             .valgrind = false,
             .optimize_mode = optimize_mode,
             .structured_cfg = comp.root_mod.structured_cfg,
-            .unwind_tables = unwind_tables,
+            // See the `-fno-exceptions` logic for WASI.
+            // The old 32-bit x86 variant of SEH doesn't use tables.
+            .unwind_tables = if (target.os.tag == .wasi or (target.cpu.arch == .x86 and target.os.tag == .windows))
+                .none
+            else
+                .@"async",
             .pic = comp.root_mod.pic,
         },
         .global = config,
diff --git a/src/libunwind.zig b/src/libunwind.zig
index 1e101da229..4b3583e1cd 100644
--- a/src/libunwind.zig
+++ b/src/libunwind.zig
@@ -65,7 +65,8 @@ pub fn buildStaticLib(comp: *Compilation, prog_node: std.Progress.Node) BuildErr
             .sanitize_c = false,
             .sanitize_thread = false,
             // necessary so that libunwind can unwind through its own stack frames
-            .unwind_tables = true,
+            // The old 32-bit x86 variant of SEH doesn't use tables.
+            .unwind_tables = if (target.cpu.arch == .x86 and target.os.tag == .windows) .none else .@"async",
             .pic = if (target_util.supports_fpic(target)) true else null,
             .optimize_mode = comp.compilerRtOptMode(),
         },
diff --git a/src/main.zig b/src/main.zig
index 23c4d7507e..1f8bd8d065 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -510,6 +510,7 @@ const usage_build_generic =
     \\  -ffuzz                    Enable fuzz testing instrumentation
     \\  -fno-fuzz                 Disable fuzz testing instrumentation
     \\  -funwind-tables           Always produce unwind table entries for all functions
+    \\  -fasync-unwind-tables     Always produce asynchronous unwind table entries for all functions
     \\  -fno-unwind-tables        Never produce unwind table entries
     \\  -ferror-tracing           Enable error tracing in ReleaseFast mode
     \\  -fno-error-tracing        Disable error tracing in Debug and ReleaseSafe mode
@@ -1385,9 +1386,11 @@ fn buildOutputType(
                     } else if (mem.eql(u8, arg, "-fno-lto")) {
                         create_module.opts.lto = false;
                     } else if (mem.eql(u8, arg, "-funwind-tables")) {
-                        mod_opts.unwind_tables = true;
+                        mod_opts.unwind_tables = .sync;
+                    } else if (mem.eql(u8, arg, "-fasync-unwind-tables")) {
+                        mod_opts.unwind_tables = .@"async";
                     } else if (mem.eql(u8, arg, "-fno-unwind-tables")) {
-                        mod_opts.unwind_tables = false;
+                        mod_opts.unwind_tables = .none;
                     } else if (mem.eql(u8, arg, "-fstack-check")) {
                         mod_opts.stack_check = true;
                     } else if (mem.eql(u8, arg, "-fno-stack-check")) {
@@ -1973,8 +1976,27 @@ fn buildOutputType(
                         }
                     },
                     .no_stack_protector => mod_opts.stack_protector = 0,
-                    .unwind_tables => mod_opts.unwind_tables = true,
-                    .no_unwind_tables => mod_opts.unwind_tables = false,
+                    // The way these unwind table options are processed in GCC and Clang is crazy
+                    // convoluted, and we also don't know the target triple here, so this is all
+                    // best-effort.
+                    .unwind_tables => if (mod_opts.unwind_tables) |uwt| switch (uwt) {
+                        .none => {
+                            mod_opts.unwind_tables = .sync;
+                        },
+                        .sync, .@"async" => {},
+                    } else {
+                        mod_opts.unwind_tables = .sync;
+                    },
+                    .no_unwind_tables => mod_opts.unwind_tables = .none,
+                    .asynchronous_unwind_tables => mod_opts.unwind_tables = .@"async",
+                    .no_asynchronous_unwind_tables => if (mod_opts.unwind_tables) |uwt| switch (uwt) {
+                        .none, .sync => {},
+                        .@"async" => {
+                            mod_opts.unwind_tables = .sync;
+                        },
+                    } else {
+                        mod_opts.unwind_tables = .sync;
+                    },
                     .nostdlib => {
                         create_module.opts.ensure_libc_on_non_freestanding = false;
                         create_module.opts.ensure_libcpp_on_non_freestanding = false;
@@ -2788,8 +2810,15 @@ fn buildOutputType(
             create_module.opts.any_sanitize_thread = true;
         if (mod_opts.fuzz == true)
             create_module.opts.any_fuzz = true;
-        if (mod_opts.unwind_tables == true)
-            create_module.opts.any_unwind_tables = true;
+        if (mod_opts.unwind_tables) |uwt| switch (uwt) {
+            .none => {},
+            .sync => if (create_module.opts.any_unwind_tables == .none) {
+                create_module.opts.any_unwind_tables = .sync;
+            },
+            .@"async" => {
+                create_module.opts.any_unwind_tables = .@"async";
+            },
+        };
         if (mod_opts.strip == false)
             create_module.opts.any_non_stripped = true;
         if (mod_opts.error_tracing == true)
@@ -5713,6 +5742,8 @@ pub const ClangArgIterator = struct {
         no_lto,
         unwind_tables,
         no_unwind_tables,
+        asynchronous_unwind_tables,
+        no_asynchronous_unwind_tables,
         nostdlib,
         nostdlib_cpp,
         shared,
@@ -7435,8 +7466,15 @@ fn handleModArg(
         create_module.opts.any_sanitize_thread = true;
     if (mod_opts.fuzz == true)
         create_module.opts.any_fuzz = true;
-    if (mod_opts.unwind_tables == true)
-        create_module.opts.any_unwind_tables = true;
+    if (mod_opts.unwind_tables) |uwt| switch (uwt) {
+        .none => {},
+        .sync => if (create_module.opts.any_unwind_tables == .none) {
+            create_module.opts.any_unwind_tables = .sync;
+        },
+        .@"async" => {
+            create_module.opts.any_unwind_tables = .@"async";
+        },
+    };
     if (mod_opts.strip == false)
         create_module.opts.any_non_stripped = true;
     if (mod_opts.error_tracing == true)
diff --git a/src/mingw.zig b/src/mingw.zig
index cdee9acb07..8473a7a93b 100644
--- a/src/mingw.zig
+++ b/src/mingw.zig
@@ -24,6 +24,10 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
     var arena_allocator = std.heap.ArenaAllocator.init(comp.gpa);
     defer arena_allocator.deinit();
     const arena = arena_allocator.allocator();
+    const target = comp.getTarget();
+
+    // The old 32-bit x86 variant of SEH doesn't use tables.
+    const unwind_tables: std.builtin.UnwindTables = if (target.cpu.arch != .x86) .@"async" else .none;
 
     switch (crt_file) {
         .crt2_o => {
@@ -41,7 +45,9 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
                     .owner = undefined,
                 },
             };
-            return comp.build_crt_file("crt2", .Obj, .@"mingw-w64 crt2.o", prog_node, &files, .{});
+            return comp.build_crt_file("crt2", .Obj, .@"mingw-w64 crt2.o", prog_node, &files, .{
+                .unwind_tables = unwind_tables,
+            });
         },
 
         .dllcrt2_o => {
@@ -56,7 +62,9 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
                     .owner = undefined,
                 },
             };
-            return comp.build_crt_file("dllcrt2", .Obj, .@"mingw-w64 dllcrt2.o", prog_node, &files, .{});
+            return comp.build_crt_file("dllcrt2", .Obj, .@"mingw-w64 dllcrt2.o", prog_node, &files, .{
+                .unwind_tables = unwind_tables,
+            });
         },
 
         .mingw32_lib => {
@@ -73,7 +81,6 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
                     .owner = undefined,
                 });
             }
-            const target = comp.getTarget();
             if (target.cpu.arch == .x86 or target.cpu.arch == .x86_64) {
                 for (mingw32_x86_src) |dep| {
                     try c_source_files.append(.{
@@ -118,7 +125,9 @@ pub fn buildCrtFile(comp: *Compilation, crt_file: CrtFile, prog_node: std.Progre
             } else {
                 @panic("unsupported arch");
             }
-            return comp.build_crt_file("mingw32", .Lib, .@"mingw-w64 mingw32.lib", prog_node, c_source_files.items, .{});
+            return comp.build_crt_file("mingw32", .Lib, .@"mingw-w64 mingw32.lib", prog_node, c_source_files.items, .{
+                .unwind_tables = unwind_tables,
+            });
         },
     }
 }
diff --git a/src/target.zig b/src/target.zig
index a1c9a19724..37f2cd50da 100644
--- a/src/target.zig
+++ b/src/target.zig
@@ -4,6 +4,7 @@ const assert = std.debug.assert;
 const Type = @import("Type.zig");
 const AddressSpace = std.builtin.AddressSpace;
 const Alignment = @import("InternPool.zig").Alignment;
+const Compilation = @import("Compilation.zig");
 const Feature = @import("Zcu.zig").Feature;
 
 pub const default_stack_protector_buffer_size = 4;
@@ -408,8 +409,16 @@ pub fn clangSupportsNoImplicitFloatArg(target: std.Target) bool {
     };
 }
 
-pub fn needUnwindTables(target: std.Target) bool {
-    return target.os.tag == .windows or target.isDarwin() or std.debug.Dwarf.abi.supportsUnwinding(target);
+pub fn needUnwindTables(target: std.Target, libunwind: bool, libtsan: bool) std.builtin.UnwindTables {
+    if (target.os.tag == .windows) {
+        // The old 32-bit x86 variant of SEH doesn't use tables.
+        return if (target.cpu.arch != .x86) .@"async" else .none;
+    }
+    if (target.os.tag.isDarwin()) return .@"async";
+    if (libunwind) return .@"async";
+    if (libtsan) return .@"async";
+    if (std.debug.Dwarf.abi.supportsUnwinding(target)) return .@"async";
+    return .none;
 }
 
 pub fn defaultAddressSpace(