From 566cc4f99d03075f396b3ca13ee140fdcd80d37a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sat, 18 Jan 2025 14:55:58 +0100
Subject: [PATCH 1/4] compiler: Fix @import("builtin").unwind_tables logic.

---
 src/Package/Module.zig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Package/Module.zig b/src/Package/Module.zig
index af91b01c9a8e..433a9b6adef9 100644
--- a/src/Package/Module.zig
+++ b/src/Package/Module.zig
@@ -387,7 +387,7 @@ 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,
+            .unwind_tables = unwind_tables,
             .is_test = options.global.is_test,
             .single_threaded = single_threaded,
             .link_libc = options.global.link_libc,

From 4de661ef18d4cdc7f859c8bc1990e8a0519163db Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sat, 18 Jan 2025 13:54:05 +0100
Subject: [PATCH 2/4] start: Don't emit CFI directives if unwind tables are
 disabled.

---
 lib/std/start.zig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/std/start.zig b/lib/std/start.zig
index 9da0cb2ec61b..8b0d6183cfea 100644
--- a/lib/std/start.zig
+++ b/lib/std/start.zig
@@ -231,8 +231,8 @@ fn _start() callconv(.naked) noreturn {
     }
 
     // This is the first userspace frame. Prevent DWARF-based unwinders from unwinding further. We
-    // prevent FP-based unwinders from unwinding further by zeroing the register further below.
-    asm volatile (switch (native_arch) {
+    // prevent FP-based unwinders from unwinding further by zeroing the register below.
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (switch (native_arch) {
             .arc => ".cfi_undefined blink",
             .arm, .armeb, .thumb, .thumbeb => "", // https://github.com/llvm/llvm-project/issues/115891
             .aarch64, .aarch64_be => ".cfi_undefined lr",

From 8a78d875cc1cdab2648e7413fc0d2eea5afc6991 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sat, 18 Jan 2025 14:09:47 +0100
Subject: [PATCH 3/4] std.os.linux: Don't emit CFI directives if unwind tables
 are disabled.

---
 lib/std/os/linux/aarch64.zig     | 8 +++++++-
 lib/std/os/linux/hexagon.zig     | 6 +++++-
 lib/std/os/linux/loongarch64.zig | 5 +++++
 lib/std/os/linux/mips.zig        | 5 +++++
 lib/std/os/linux/mips64.zig      | 5 +++++
 lib/std/os/linux/powerpc.zig     | 5 +++++
 lib/std/os/linux/powerpc64.zig   | 5 +++++
 lib/std/os/linux/riscv32.zig     | 8 +++++++-
 lib/std/os/linux/riscv64.zig     | 8 +++++++-
 lib/std/os/linux/s390x.zig       | 5 +++++
 lib/std/os/linux/sparc64.zig     | 5 +++++
 lib/std/os/linux/x86.zig         | 5 +++++
 lib/std/os/linux/x86_64.zig      | 8 +++++++-
 13 files changed, 73 insertions(+), 5 deletions(-)

diff --git a/lib/std/os/linux/aarch64.zig b/lib/std/os/linux/aarch64.zig
index db304a3a33b4..302c58ac2bcf 100644
--- a/lib/std/os/linux/aarch64.zig
+++ b/lib/std/os/linux/aarch64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -122,7 +123,12 @@ pub fn clone() callconv(.Naked) usize {
         \\      ret
         \\
         \\      // child
-        \\1:    .cfi_undefined lr
+        \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
+        \\     .cfi_undefined lr
+    );
+    asm volatile (
         \\      mov fp, 0
         \\      mov lr, 0
         \\
diff --git a/lib/std/os/linux/hexagon.zig b/lib/std/os/linux/hexagon.zig
index 0839ea8297a0..0b5cbb208ee8 100644
--- a/lib/std/os/linux/hexagon.zig
+++ b/lib/std/os/linux/hexagon.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const iovec = std.posix.iovec;
 const iovec_const = std.posix.iovec_const;
@@ -117,8 +118,11 @@ pub fn clone() callconv(.Naked) usize {
         \\
         \\ p0 = cmp.eq(r0, #0)
         \\ if (!p0) dealloc_return
-        \\
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined r31
+    );
+    asm volatile (
         \\ r30 = #0
         \\ r31 = #0
         \\
diff --git a/lib/std/os/linux/loongarch64.zig b/lib/std/os/linux/loongarch64.zig
index b52f1d10b137..ce57a6713a9b 100644
--- a/lib/std/os/linux/loongarch64.zig
+++ b/lib/std/os/linux/loongarch64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const linux = std.os.linux;
 const SYS = linux.SYS;
@@ -121,7 +122,11 @@ pub fn clone() callconv(.Naked) usize {
         \\ beqz    $a0, 1f         # whether child process
         \\ jirl    $zero, $ra, 0   # parent process return
         \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined 1
+    );
+    asm volatile (
         \\ move    $fp, $zero
         \\ move    $ra, $zero
         \\
diff --git a/lib/std/os/linux/mips.zig b/lib/std/os/linux/mips.zig
index 5d786ccde7f6..5ebe6bd68658 100644
--- a/lib/std/os/linux/mips.zig
+++ b/lib/std/os/linux/mips.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -231,7 +232,11 @@ pub fn clone() callconv(.Naked) usize {
         \\  jr $ra
         \\  nop
         \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\  .cfi_undefined $ra
+    );
+    asm volatile (
         \\  move $fp, $zero
         \\  move $ra, $zero
         \\
diff --git a/lib/std/os/linux/mips64.zig b/lib/std/os/linux/mips64.zig
index 256c911bbe58..0d0a1104c12c 100644
--- a/lib/std/os/linux/mips64.zig
+++ b/lib/std/os/linux/mips64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -210,7 +211,11 @@ pub fn clone() callconv(.Naked) usize {
         \\ jr $ra
         \\ nop
         \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined $ra
+    );
+    asm volatile (
         \\ move $fp, $zero
         \\ move $ra, $zero
         \\
diff --git a/lib/std/os/linux/powerpc.zig b/lib/std/os/linux/powerpc.zig
index 9dde326e1b04..591575cb02a7 100644
--- a/lib/std/os/linux/powerpc.zig
+++ b/lib/std/os/linux/powerpc.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -176,7 +177,11 @@ pub fn clone() callconv(.Naked) usize {
         \\
         \\ #else: we're the child
         \\ 2:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined lr
+    );
+    asm volatile (
         \\ li 31, 0
         \\ mtlr 0
         \\
diff --git a/lib/std/os/linux/powerpc64.zig b/lib/std/os/linux/powerpc64.zig
index 6a1f98a65fba..419c9f062985 100644
--- a/lib/std/os/linux/powerpc64.zig
+++ b/lib/std/os/linux/powerpc64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -161,7 +162,11 @@ pub fn clone() callconv(.Naked) usize {
         \\  bnelr cr7
         \\
         \\  # we're the child
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\  .cfi_undefined lr
+    );
+    asm volatile (
         \\  li    31, 0
         \\  mtlr   0
         \\
diff --git a/lib/std/os/linux/riscv32.zig b/lib/std/os/linux/riscv32.zig
index dc444a19560b..4df6e1671f93 100644
--- a/lib/std/os/linux/riscv32.zig
+++ b/lib/std/os/linux/riscv32.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const iovec = std.posix.iovec;
 const iovec_const = std.posix.iovec_const;
@@ -120,7 +121,12 @@ pub fn clone() callconv(.Naked) usize {
         \\    ret
         \\
         \\    # Child
-        \\1:  .cfi_undefined ra
+        \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
+        \\    .cfi_undefined ra
+    );
+    asm volatile (
         \\    mv fp, zero
         \\    mv ra, zero
         \\
diff --git a/lib/std/os/linux/riscv64.zig b/lib/std/os/linux/riscv64.zig
index 45ba568c1bf9..c402e9e894ae 100644
--- a/lib/std/os/linux/riscv64.zig
+++ b/lib/std/os/linux/riscv64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const iovec = std.posix.iovec;
 const iovec_const = std.posix.iovec_const;
@@ -120,7 +121,12 @@ pub fn clone() callconv(.Naked) usize {
         \\    ret
         \\
         \\    # Child
-        \\1:  .cfi_undefined ra
+        \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
+        \\    .cfi_undefined ra
+    );
+    asm volatile (
         \\    mv fp, zero
         \\    mv ra, zero
         \\
diff --git a/lib/std/os/linux/s390x.zig b/lib/std/os/linux/s390x.zig
index 8fbe1c930b3b..337e36a574ab 100644
--- a/lib/std/os/linux/s390x.zig
+++ b/lib/std/os/linux/s390x.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const iovec = std.posix.iovec;
 const iovec_const = std.posix.iovec_const;
@@ -134,7 +135,11 @@ pub fn clone() callconv(.Naked) usize {
         \\bnzr %%r14
         \\
         \\# we're the child
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\.cfi_undefined %%r14
+    );
+    asm volatile (
         \\lghi %%r11, 0
         \\lghi %%r14, 0
         \\
diff --git a/lib/std/os/linux/sparc64.zig b/lib/std/os/linux/sparc64.zig
index 17df65feb72d..90cb799e02be 100644
--- a/lib/std/os/linux/sparc64.zig
+++ b/lib/std/os/linux/sparc64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const pid_t = linux.pid_t;
@@ -215,7 +216,11 @@ pub fn clone() callconv(.Naked) usize {
         \\ restore
         \\2:
         \\ # Child process
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined %%i7
+    );
+    asm volatile (
         \\ mov %%g0, %%fp
         \\ mov %%g0, %%i7
         \\
diff --git a/lib/std/os/linux/x86.zig b/lib/std/os/linux/x86.zig
index cb746e52a8dc..0cde6d805e78 100644
--- a/lib/std/os/linux/x86.zig
+++ b/lib/std/os/linux/x86.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -156,7 +157,11 @@ pub fn clone() callconv(.Naked) usize {
         \\  retl
         \\
         \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\  .cfi_undefined %%eip
+    );
+    asm volatile (
         \\  xorl %%ebp,%%ebp
         \\
         \\  popl %%eax
diff --git a/lib/std/os/linux/x86_64.zig b/lib/std/os/linux/x86_64.zig
index 44a37345f0f4..1c5105d6247d 100644
--- a/lib/std/os/linux/x86_64.zig
+++ b/lib/std/os/linux/x86_64.zig
@@ -1,3 +1,4 @@
+const builtin = @import("builtin");
 const std = @import("../../std.zig");
 const maxInt = std.math.maxInt;
 const linux = std.os.linux;
@@ -117,7 +118,12 @@ pub fn clone() callconv(.Naked) usize {
         \\      jz 1f
         \\      retq
         \\
-        \\1:    .cfi_undefined %%rip
+        \\1:
+    );
+    if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
+        \\      .cfi_undefined %%rip
+    );
+    asm volatile (
         \\      xorl %%ebp,%%ebp
         \\
         \\      popq %%rdi

From 45bb4f955c8c8be40ed8b2247eaaa70661cf1b3d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sat, 18 Jan 2025 14:32:55 +0100
Subject: [PATCH 4/4] test: Add a standalone test for omitting CFI directives.

---
 test/standalone/build.zig.zon      |  3 ++
 test/standalone/omit_cfi/build.zig | 67 ++++++++++++++++++++++++++++++
 test/standalone/omit_cfi/main.zig  |  1 +
 3 files changed, 71 insertions(+)
 create mode 100644 test/standalone/omit_cfi/build.zig
 create mode 100644 test/standalone/omit_cfi/main.zig

diff --git a/test/standalone/build.zig.zon b/test/standalone/build.zig.zon
index 06ebe980d1b0..9863e7cc6d46 100644
--- a/test/standalone/build.zig.zon
+++ b/test/standalone/build.zig.zon
@@ -183,6 +183,9 @@
         .empty_global_error_set = .{
             .path = "empty_global_error_set",
         },
+        .omit_cfi = .{
+            .path = "omit_cfi",
+        },
     },
     .paths = .{
         "build.zig",
diff --git a/test/standalone/omit_cfi/build.zig b/test/standalone/omit_cfi/build.zig
new file mode 100644
index 000000000000..62f9fed471b2
--- /dev/null
+++ b/test/standalone/omit_cfi/build.zig
@@ -0,0 +1,67 @@
+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    inline for (.{
+        .aarch64,
+        .aarch64_be,
+        .hexagon,
+        .loongarch64,
+        .mips,
+        .mipsel,
+        .mips64,
+        .mips64el,
+        .powerpc,
+        .powerpcle,
+        .powerpc64,
+        .powerpc64le,
+        .riscv32,
+        .riscv64,
+        .s390x,
+        .sparc64,
+        .x86,
+        .x86_64,
+    }) |arch| {
+        const target = b.resolveTargetQuery(.{
+            .cpu_arch = arch,
+            .os_tag = .linux,
+        });
+
+        const omit_dbg = b.addExecutable(.{
+            .name = b.fmt("{s}-linux-omit-dbg", .{@tagName(arch)}),
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("main.zig"),
+                .target = target,
+                .optimize = .Debug,
+                // We are mainly concerned with CFI directives in our non-libc startup code and syscall
+                // code, so make it explicit that we don't want libc.
+                .link_libc = false,
+                .strip = true,
+            }),
+        });
+
+        const omit_uwt = b.addExecutable(.{
+            .name = b.fmt("{s}-linux-omit-uwt", .{@tagName(arch)}),
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("main.zig"),
+                .target = target,
+                .optimize = .Debug,
+                .link_libc = false,
+                .unwind_tables = .none,
+            }),
+        });
+
+        const omit_both = b.addExecutable(.{
+            .name = b.fmt("{s}-linux-omit-both", .{@tagName(arch)}),
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("main.zig"),
+                .target = target,
+                .optimize = .Debug,
+                .link_libc = false,
+                .strip = true,
+                .unwind_tables = .none,
+            }),
+        });
+
+        inline for (.{ omit_dbg, omit_uwt, omit_both }) |step| b.installArtifact(step);
+    }
+}
diff --git a/test/standalone/omit_cfi/main.zig b/test/standalone/omit_cfi/main.zig
new file mode 100644
index 000000000000..902b554db075
--- /dev/null
+++ b/test/standalone/omit_cfi/main.zig
@@ -0,0 +1 @@
+pub fn main() void {}