better awareness of unwind tables

 * stage1 backend allows configuring the uwtables function attr
   via a flag rather than its own logic.
 * stage2 defaults to enabling uwtable attr when
   linking libunwind, or always on windows
 * stage2 makes link_eh_frame_hdr true automatically if uwtable
   attr is set to be on for zig functions
 * CLI: add -funwind-tables and -fno-unwind-tables to allow the user to
   override the defaults.
 * hook it up to `zig cc`

closes #9046

1 files changed, 26 insertions, 12 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 3295f9fc3c..00c5937394 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -81,6 +81,7 @@ verbose_llvm_cpu_features: bool,
 disable_c_depfile: bool,
 time_report: bool,
 stack_report: bool,
+unwind_tables: bool,
 
 c_source_files: []const CSourceFile,
 clang_argv: []const []const u8,
@@ -665,6 +666,7 @@ pub const InitOptions = struct {
     want_tsan: ?bool = null,
     want_compiler_rt: ?bool = null,
     want_lto: ?bool = null,
+    want_unwind_tables: ?bool = null,
     use_llvm: ?bool = null,
     use_lld: ?bool = null,
     use_clang: ?bool = null,
@@ -823,8 +825,20 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             return error.MachineCodeModelNotSupported;
         }
 
+        const tsan = options.want_tsan orelse false;
+        // TSAN is implemented in C++ so it requires linking libc++.
+        const link_libcpp = options.link_libcpp or tsan;
+        const link_libc = link_libcpp or options.link_libc or
+            target_util.osRequiresLibC(options.target);
+
+        const link_libunwind = options.link_libunwind or
+            (link_libcpp and target_util.libcNeedsLibUnwind(options.target));
+        const unwind_tables = options.want_unwind_tables orelse
+            (link_libunwind or target_util.needUnwindTables(options.target));
+        const link_eh_frame_hdr = options.link_eh_frame_hdr or unwind_tables;
+
         // Make a decision on whether to use LLD or our own linker.
-        const use_lld = if (options.use_lld) |explicit| explicit else blk: {
+        const use_lld = options.use_lld orelse blk: {
             if (!build_options.have_llvm)
                 break :blk false;
 
@@ -843,7 +857,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
                 options.frameworks.len != 0 or
                 options.system_libs.len != 0 or
                 options.link_libc or options.link_libcpp or
-                options.link_eh_frame_hdr or
+                link_eh_frame_hdr or
                 options.link_emit_relocs or
                 options.output_mode == .Lib or
                 options.lld_argv.len != 0 or
@@ -902,15 +916,6 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             }
         };
 
-        const tsan = options.want_tsan orelse false;
-        // TSAN is implemented in C++ so it requires linking libc++.
-        const link_libcpp = options.link_libcpp or tsan;
-        const link_libc = link_libcpp or options.link_libc or
-            target_util.osRequiresLibC(options.target);
-
-        const link_libunwind = options.link_libunwind or
-            (link_libcpp and target_util.libcNeedsLibUnwind(options.target));
-
         const must_dynamic_link = dl: {
             if (target_util.cannotDynamicLink(options.target))
                 break :dl false;
@@ -1080,6 +1085,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
         cache.hash.add(pic);
         cache.hash.add(pie);
         cache.hash.add(lto);
+        cache.hash.add(unwind_tables);
         cache.hash.add(tsan);
         cache.hash.add(stack_check);
         cache.hash.add(red_zone);
@@ -1312,7 +1318,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             .linker_script = options.linker_script,
             .version_script = options.version_script,
             .gc_sections = options.linker_gc_sections,
-            .eh_frame_hdr = options.link_eh_frame_hdr,
+            .eh_frame_hdr = link_eh_frame_hdr,
             .emit_relocs = options.link_emit_relocs,
             .rdynamic = options.rdynamic,
             .extra_lld_args = options.lld_argv,
@@ -1376,6 +1382,7 @@ pub fn create(gpa: *Allocator, options: InitOptions) !*Compilation {
             .color = options.color,
             .time_report = options.time_report,
             .stack_report = options.stack_report,
+            .unwind_tables = unwind_tables,
             .test_filter = options.test_filter,
             .test_name_prefix = options.test_name_prefix,
             .test_evented_io = options.test_evented_io,
@@ -2983,6 +2990,12 @@ pub fn addCCArgs(
             if (target_util.supports_fpic(target) and comp.bin_file.options.pic) {
                 try argv.append("-fPIC");
             }
+
+            if (comp.unwind_tables) {
+                try argv.append("-funwind-tables");
+            } else {
+                try argv.append("-fno-unwind-tables");
+            }
         },
         .shared_library, .ll, .bc, .unknown, .static_library, .object, .zig => {},
         .assembly => {
@@ -3948,6 +3961,7 @@ fn updateStage1Module(comp: *Compilation, main_progress_node: *std.Progress.Node
         .pic = comp.bin_file.options.pic,
         .pie = comp.bin_file.options.pie,
         .lto = comp.bin_file.options.lto,
+        .unwind_tables = comp.unwind_tables,
         .link_libc = comp.bin_file.options.link_libc,
         .link_libcpp = comp.bin_file.options.link_libcpp,
         .strip = comp.bin_file.options.strip,