std.debug: LoongArch and RISC-V unwind support + some minor cleanups

lib/std/debug.zig

@@ -61,28 +61,12 @@ pub const cpu_context = @import("debug/cpu_context.zig");
 /// ```
 pub const SelfInfo = if (@hasDecl(root, "debug") and @hasDecl(root.debug, "SelfInfo"))
     root.debug.SelfInfo
-else switch (native_os) {
-    .linux,
-    .netbsd,
-    .freebsd,
-    .dragonfly,
-    .openbsd,
-    .solaris,
-    .illumos,
-    => @import("debug/SelfInfo/Elf.zig"),
-
-    .macos,
-    .ios,
-    .watchos,
-    .tvos,
-    .visionos,
-    => @import("debug/SelfInfo/Darwin.zig"),
-
-    .uefi,
-    .windows,
-    => @import("debug/SelfInfo/Windows.zig"),
-
-    else => void,
+else switch (std.Target.ObjectFormat.default(native_os, native_arch)) {
+    .coff => if (native_os == .windows) @import("debug/SelfInfo/Windows.zig") else void,
+    .elf => @import("debug/SelfInfo/Elf.zig"),
+    .macho => @import("debug/SelfInfo/MachO.zig"),
+    .goff, .plan9, .spirv, .wasm, .xcoff => void,
+    .c, .hex, .raw => unreachable,
 };
 
 pub const SelfInfoError = error{

lib/std/debug/Dwarf.zig

@@ -1429,30 +1429,36 @@ pub fn compactUnwindToDwarfRegNumber(unwind_reg_number: u3) !u16 {
 /// Returns `null` for CPU architectures without an instruction pointer register.
 pub fn ipRegNum(arch: std.Target.Cpu.Arch) ?u16 {
     return switch (arch) {
+        .aarch64, .aarch64_be => 32,
+        .arm, .armeb, .thumb, .thumbeb => 15,
+        .loongarch32, .loongarch64 => 32,
+        .riscv32, .riscv32be, .riscv64, .riscv64be => 32,
         .x86 => 8,
         .x86_64 => 16,
-        .arm, .armeb, .thumb, .thumbeb => 15,
-        .aarch64, .aarch64_be => 32,
         else => null,
     };
 }
 
 pub fn fpRegNum(arch: std.Target.Cpu.Arch) u16 {
     return switch (arch) {
+        .aarch64, .aarch64_be => 29,
+        .arm, .armeb, .thumb, .thumbeb => 11,
+        .loongarch32, .loongarch64 => 22,
+        .riscv32, .riscv32be, .riscv64, .riscv64be => 8,
         .x86 => 5,
         .x86_64 => 6,
-        .arm, .armeb, .thumb, .thumbeb => 11,
-        .aarch64, .aarch64_be => 29,
         else => unreachable,
     };
 }
 
 pub fn spRegNum(arch: std.Target.Cpu.Arch) u16 {
     return switch (arch) {
+        .aarch64, .aarch64_be => 31,
+        .arm, .armeb, .thumb, .thumbeb => 13,
+        .loongarch32, .loongarch64 => 3,
+        .riscv32, .riscv32be, .riscv64, .riscv64be => 2,
         .x86 => 4,
         .x86_64 => 7,
-        .arm, .armeb, .thumb, .thumbeb => 13,
-        .aarch64, .aarch64_be => 31,
         else => unreachable,
     };
 }
@@ -1470,10 +1476,6 @@ pub fn supportsUnwinding(target: *const std.Target) bool {
         .spirv64,
         => false,
 
-        // Enabling this causes relocation errors such as:
-        // error: invalid relocation type R_RISCV_SUB32 at offset 0x20
-        .riscv64, .riscv64be, .riscv32, .riscv32be => false,
-
         // Conservative guess. Feel free to update this logic with any targets
         // that are known to not support Dwarf unwinding.
         else => true,

lib/std/debug/Dwarf/Unwind/VirtualMachine.zig

@@ -256,7 +256,18 @@ fn evalInstructions(
                 .offset = cfa.offset_sf * cie.data_alignment_factor,
             } },
             .def_cfa_reg => |register| switch (vm.current_row.cfa) {
-                .none, .expression => return error.InvalidOperation,
+                .none => {
+                    // According to the DWARF specification, this is not valid, because this
+                    // instruction can only be used to replace the register if the rule is already a
+                    // `.reg_off`. However, this is emitted in practice by GNU toolchains for some
+                    // targets, and so by convention is interpreted as equivalent to `.def_cfa` with
+                    // an offset of 0.
+                    vm.current_row.cfa = .{ .reg_off = .{
+                        .register = register,
+                        .offset = 0,
+                    } };
+                },
+                .expression => return error.InvalidOperation,
                 .reg_off => |*ro| ro.register = register,
             },
             .def_cfa_offset => |offset| switch (vm.current_row.cfa) {

lib/std/debug/SelfInfo/Elf.zig

@@ -84,12 +84,35 @@ pub const can_unwind: bool = s: {
     // Notably, we are yet to support unwinding on ARM. There, unwinding is not done through
     // `.eh_frame`, but instead with the `.ARM.exidx` section, which has a different format.
     const archs: []const std.Target.Cpu.Arch = switch (builtin.target.os.tag) {
-        .linux => &.{ .x86, .x86_64, .aarch64, .aarch64_be },
-        .netbsd => &.{ .x86, .x86_64, .aarch64, .aarch64_be },
-        .freebsd => &.{ .x86_64, .aarch64, .aarch64_be },
-        .openbsd => &.{.x86_64},
-        .solaris => &.{ .x86, .x86_64 },
-        .illumos => &.{ .x86, .x86_64 },
+        .linux => &.{
+            .aarch64,
+            .aarch64_be,
+            .loongarch64,
+            .riscv32,
+            .riscv64,
+            .x86,
+            .x86_64,
+        },
+        .netbsd => &.{
+            .aarch64,
+            .aarch64_be,
+            .x86,
+            .x86_64,
+        },
+        .freebsd => &.{
+            .x86_64,
+            .aarch64,
+        },
+        .openbsd => &.{
+            .x86_64,
+        },
+        .solaris => &.{
+            .x86_64,
+        },
+        .illumos => &.{
+            .x86,
+            .x86_64,
+        },
         else => unreachable,
     };
     for (archs) |a| {

lib/std/debug/SelfInfo/Darwin.zig → lib/std/debug/SelfInfo/MachO.zig

@@ -371,7 +371,7 @@ fn unwindFrameInner(si: *SelfInfo, gpa: Allocator, context: *UnwindContext) !usi
                 return context.next(gpa, &rules);
             },
         },
-        .aarch64, .aarch64_be => switch (encoding.mode.arm64) {
+        .aarch64 => switch (encoding.mode.arm64) {
             .OLD => return error.UnsupportedDebugInfo,
             .FRAMELESS => ip: {
                 const sp = (try dwarfRegNative(&context.cpu_state, sp_reg_num)).*;

lib/std/debug/SelfInfo/Windows.zig

@@ -88,7 +88,7 @@ pub const UnwindContext = struct {
                     .R15 = ctx.gprs.get(.r15),
                     .Rip = ctx.gprs.get(.rip),
                 }),
-                .aarch64, .aarch64_be => .{
+                .aarch64 => .{
                     .ContextFlags = 0,
                     .Cpsr = 0,
                     .DUMMYUNIONNAME = .{ .X = ctx.x },