From 4c81a496e7c979755d9fc74734ab740a828c4491 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Thu, 16 Oct 2025 17:31:55 +0200
Subject: [PATCH] std.debug: add CPU context and DWARF mappings for arc

---
 lib/std/debug/Dwarf.zig        |  3 ++
 lib/std/debug/SelfInfo/Elf.zig |  3 +-
 lib/std/debug/cpu_context.zig  | 80 +++++++++++++++++++++++++++++++++-
 3 files changed, 83 insertions(+), 3 deletions(-)

diff --git a/lib/std/debug/Dwarf.zig b/lib/std/debug/Dwarf.zig
index 8aaf85c66b..7229dcdf4c 100644
--- a/lib/std/debug/Dwarf.zig
+++ b/lib/std/debug/Dwarf.zig
@@ -1430,6 +1430,7 @@ pub fn compactUnwindToDwarfRegNumber(unwind_reg_number: u3) !u16 {
 pub fn ipRegNum(arch: std.Target.Cpu.Arch) ?u16 {
     return switch (arch) {
         .aarch64, .aarch64_be => 32,
+        .arc => 160,
         .arm, .armeb, .thumb, .thumbeb => 15,
         .csky => 64,
         .hexagon => 76,
@@ -1452,6 +1453,7 @@ pub fn ipRegNum(arch: std.Target.Cpu.Arch) ?u16 {
 pub fn fpRegNum(arch: std.Target.Cpu.Arch) u16 {
     return switch (arch) {
         .aarch64, .aarch64_be => 29,
+        .arc => 27,
         .arm, .armeb, .thumb, .thumbeb => 11,
         .csky => 14,
         .hexagon => 30,
@@ -1474,6 +1476,7 @@ pub fn fpRegNum(arch: std.Target.Cpu.Arch) u16 {
 pub fn spRegNum(arch: std.Target.Cpu.Arch) u16 {
     return switch (arch) {
         .aarch64, .aarch64_be => 31,
+        .arc => 28,
         .arm, .armeb, .thumb, .thumbeb => 13,
         .csky => 14,
         .hexagon => 29,
diff --git a/lib/std/debug/SelfInfo/Elf.zig b/lib/std/debug/SelfInfo/Elf.zig
index e25f357803..5713542510 100644
--- a/lib/std/debug/SelfInfo/Elf.zig
+++ b/lib/std/debug/SelfInfo/Elf.zig
@@ -102,10 +102,11 @@ pub const can_unwind: bool = s: {
             .x86,
             .x86_64,
         },
-        // Not supported yet: arc, arm/armeb/thumb/thumbeb, xtensa
+        // Not supported yet: arm/armeb/thumb/thumbeb, xtensa
         .linux => &.{
             .aarch64,
             .aarch64_be,
+            .arc,
             .csky,
             .loongarch64,
             .m68k,
diff --git a/lib/std/debug/cpu_context.zig b/lib/std/debug/cpu_context.zig
index 1278e630ff..d46f9bd132 100644
--- a/lib/std/debug/cpu_context.zig
+++ b/lib/std/debug/cpu_context.zig
@@ -5,6 +5,7 @@ pub const Native = if (@hasDecl(root, "debug") and @hasDecl(root.debug, "CpuCont
     root.debug.CpuContext
 else switch (native_arch) {
     .aarch64, .aarch64_be => Aarch64,
+    .arc => Arc,
     .arm, .armeb, .thumb, .thumbeb => Arm,
     .csky => Csky,
     .hexagon => Hexagon,
@@ -35,7 +36,20 @@ pub fn fromPosixSignalContext(ctx_ptr: ?*const anyopaque) ?Native {
     const uc: *const signal_ucontext_t = @ptrCast(@alignCast(ctx_ptr));
 
     // Deal with some special cases first.
-    if (native_arch.isMIPS32() and native_os == .linux) {
+    if (native_arch == .arc and native_os == .linux) {
+        var native: Native = .{
+            .r = [_]u32{ uc.mcontext.r31, uc.mcontext.r30, 0, uc.mcontext.r28 } ++
+                uc.mcontext.r27_26 ++
+                uc.mcontext.r25_13 ++
+                uc.mcontext.r12_0,
+            .pcl = uc.mcontext.pcl,
+        };
+
+        // I have no idea why the kernel is storing these registers in such a bizarre order...
+        std.mem.reverse(native.r[0..]);
+
+        return native;
+    } else if (native_arch.isMIPS32() and native_os == .linux) {
         // The O32 kABI uses 64-bit fields for some reason.
         return .{
             .r = s: {
@@ -327,6 +341,68 @@ const X86_64 = struct {
     }
 };
 
+/// This is an `extern struct` so that inline assembly in `current` can use field offsets.
+const Arc = extern struct {
+    /// The numbered general-purpose registers r0 - r31.
+    r: [32]u32,
+    pcl: u32,
+
+    pub inline fn current() Arc {
+        var ctx: Arc = undefined;
+        asm volatile (
+            \\ st r0, [r8, 0]
+            \\ st r1, [r8, 4]
+            \\ st r2, [r8, 8]
+            \\ st r3, [r8, 12]
+            \\ st r4, [r8, 16]
+            \\ st r5, [r8, 20]
+            \\ st r6, [r8, 24]
+            \\ st r7, [r8, 28]
+            \\ st r8, [r8, 32]
+            \\ st r9, [r8, 36]
+            \\ st r10, [r8, 40]
+            \\ st r11, [r8, 44]
+            \\ st r12, [r8, 48]
+            \\ st r13, [r8, 52]
+            \\ st r14, [r8, 56]
+            \\ st r15, [r8, 60]
+            \\ st r16, [r8, 64]
+            \\ st r17, [r8, 68]
+            \\ st r18, [r8, 72]
+            \\ st r19, [r8, 76]
+            \\ st r20, [r8, 80]
+            \\ st r21, [r8, 84]
+            \\ st r22, [r8, 88]
+            \\ st r23, [r8, 92]
+            \\ st r24, [r8, 96]
+            \\ st r25, [r8, 100]
+            \\ st r26, [r8, 104]
+            \\ st r27, [r8, 108]
+            \\ st r28, [r8, 112]
+            \\ st r29, [r8, 116]
+            \\ st r30, [r8, 120]
+            \\ st r31, [r8, 124]
+            \\ st pcl, [r8, 128]
+            :
+            : [ctx] "{r8}" (&ctx),
+            : .{ .memory = true });
+        return ctx;
+    }
+
+    pub fn dwarfRegisterBytes(ctx: *Arc, register_num: u16) DwarfRegisterError![]u8 {
+        switch (register_num) {
+            0...31 => return @ptrCast(&ctx.r[register_num]),
+            160 => return @ptrCast(&ctx.pcl),
+
+            32...57 => return error.UnsupportedRegister, // Extension Core Registers
+            58...127 => return error.UnsupportedRegister, // Reserved
+            128...159 => return error.UnsupportedRegister, // f0 - f31
+
+            else => return error.InvalidRegister,
+        }
+    }
+};
+
 const Arm = struct {
     /// The numbered general-purpose registers R0 - R15.
     r: [16]u32,
@@ -1517,7 +1593,7 @@ const signal_ucontext_t = switch (native_os) {
                         _count: u32,
                     },
                     _status32: u32,
-                    pc: u32,
+                    pcl: u32,
                     r31: u32,
                     r27_26: [2]u32,
                     r12_0: [13]u32,