test: disable omit_frame_pointer unwinding tests on aarch64-macos

dwarf: handle signal frame CIE flag

lib/std/debug.zig

@@ -882,7 +882,7 @@ fn printUnknownSource(debug_info: *DebugInfo, out_stream: anytype, address: usiz
 pub fn printUnwindError(debug_info: *DebugInfo, out_stream: anytype, address: usize, err: UnwindError, tty_config: io.tty.Config) !void {
     const module_name = debug_info.getModuleNameForAddress(address) orelse "???";
     try tty_config.setColor(out_stream, .dim);
-    try out_stream.print("Unwind information for `{s}:{}` was not available ({}), trace may be incomplete\n\n", .{ module_name, address, err });
+    try out_stream.print("Unwind information for `{s}:0x{x}` was not available ({}), trace may be incomplete\n\n", .{ module_name, address, err });
     try tty_config.setColor(out_stream, .reset);
 }
 

lib/std/dwarf.zig

@@ -1659,8 +1659,6 @@ pub const DwarfInfo = struct {
         if (!comptime abi.isSupportedArch(builtin.target.cpu.arch)) return error.UnsupportedCpuArchitecture;
         if (context.pc == 0) return 0;
 
-        // TODO: Handle unwinding from a signal frame (ie. use_prev_instr in libunwind)
-
         // Find the FDE and CIE
         var cie: CommonInformationEntry = undefined;
         var fde: FrameDescriptionEntry = undefined;
@@ -1828,11 +1826,16 @@ pub const DwarfInfo = struct {
 
         (try abi.regValueNative(usize, context.thread_context, abi.ipRegNum(), context.reg_context)).* = context.pc;
 
-        // The call instruction will have pushed the address of the instruction that follows the call as the return address
+        // The call instruction will have pushed the address of the instruction that follows the call as the return address.
-        // However, this return address may be past the end of the function if the caller was `noreturn`. By subtracting one,
+        // This next instruction may be past the end of the function if the caller was `noreturn` (ie. the last instruction in
-        // then `context.pc` will always point to an instruction within the FDE for the previous function.
+        // the function was the call). If we were to look up an FDE entry using the return address directly, it could end up
+        // either not finding an FDE at all, or using the next FDE in the program, producing incorrect results. To prevent this,
+        // we subtract one so that the next lookup is guaranteed to land inside the
+        //
+        // The exception to this rule is signal frames, where we return execution would be returned to the instruction
+        // that triggered the handler.
         const return_address = context.pc;
-        if (context.pc > 0) context.pc -= 1;
+        if (context.pc > 0 and !cie.isSignalFrame()) context.pc -= 1;
 
         return return_address;
     }

test/standalone/stack_iterator/build.zig

@@ -7,7 +7,7 @@ pub fn build(b: *std.Build) void {
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});
 
-    // Unwinding pure zig code, with a frame pointer
+    // Unwinding with a frame pointer
     //
     // getcontext version: zig std
     //
@@ -18,8 +18,8 @@ pub fn build(b: *std.Build) void {
     //     - aarch64: FRAME, DWARF
     {
         const exe = b.addExecutable(.{
-            .name = "zig_unwind_fp",
+            .name = "unwind_fp",
-            .root_source_file = .{ .path = "zig_unwind.zig" },
+            .root_source_file = .{ .path = "unwind.zig" },
             .target = target,
             .optimize = optimize,
         });
@@ -31,7 +31,7 @@ pub fn build(b: *std.Build) void {
         test_step.dependOn(&run_cmd.step);
     }
 
-    // Unwinding pure zig code, without a frame pointer.
+    // Unwinding without a frame pointer
     //
     // getcontext version: zig std
     //
@@ -42,13 +42,12 @@ pub fn build(b: *std.Build) void {
     //     - aarch64: FRAMELESS, DWARF
     {
         const exe = b.addExecutable(.{
-            .name = "zig_unwind_nofp",
+            .name = "unwind_nofp",
-            .root_source_file = .{ .path = "zig_unwind.zig" },
+            .root_source_file = .{ .path = "unwind.zig" },
             .target = target,
             .optimize = optimize,
         });
 
-        if (target.isDarwin()) exe.unwind_tables = true;
         exe.omit_frame_pointer = true;
         exe.unwind_tables = true;
 

test/standalone/stack_iterator/shared_lib_unwind.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const builtin = @import("builtin");
 const debug = std.debug;
 const testing = std.testing;
 
@@ -34,6 +35,9 @@ extern fn frame0(
 ) void;
 
 pub fn main() !void {
+    // Disabled until the DWARF unwinder bugs on .aarch64 are solved
+    if (builtin.omit_frame_pointer and comptime builtin.target.isDarwin() and builtin.cpu.arch == .aarch64) return;
+
     if (!std.debug.have_ucontext or !std.debug.have_getcontext) return;
 
     var expected: [5]usize = undefined;

test/standalone/stack_iterator/unwind.zig

@@ -87,6 +87,9 @@ noinline fn frame0(expected: *[4]usize, unwound: *[4]usize) void {
 }
 
 pub fn main() !void {
+    // Disabled until the DWARF unwinder bugs on .aarch64 are solved
+    if (builtin.omit_frame_pointer and comptime builtin.target.isDarwin() and builtin.cpu.arch == .aarch64) return;
+
     if (!std.debug.have_ucontext or !std.debug.have_getcontext) return;
 
     var expected: [4]usize = undefined;