x86_64: fix `@errorName` data

The final offset was clobbering the first error name, which is revealed
by an out of bounds when the global error set is empty.

Closes #22362

3 files changed, 31 insertions, 0 deletions

diff --git a/test/standalone/build.zig.zon b/test/standalone/build.zig.zon
index 30ec07823b..06ebe980d1 100644
--- a/test/standalone/build.zig.zon
+++ b/test/standalone/build.zig.zon
@@ -180,6 +180,9 @@
         .run_output_caching = .{
             .path = "run_output_caching",
         },
+        .empty_global_error_set = .{
+            .path = "empty_global_error_set",
+        },
     },
     .paths = .{
         "build.zig",
diff --git a/test/standalone/empty_global_error_set/build.zig b/test/standalone/empty_global_error_set/build.zig
new file mode 100644
index 0000000000..ad971aa6d1
--- /dev/null
+++ b/test/standalone/empty_global_error_set/build.zig
@@ -0,0 +1,24 @@
+const std = @import("std");
+const builtin = @import("builtin");
+
+pub fn build(b: *std.Build) void {
+    const test_step = b.step("test", "Test it");
+    b.default_step = test_step;
+
+    for ([_]bool{ false, true }) |use_llvm| {
+        const main = b.addObject(.{
+            .name = "main",
+            .root_module = b.createModule(.{
+                .root_source_file = b.path("main.zig"),
+                .target = b.resolveTargetQuery(.{
+                    .cpu_arch = .x86_64,
+                    .os_tag = .linux,
+                }),
+            }),
+            .use_llvm = use_llvm,
+            .use_lld = use_llvm,
+        });
+        _ = main.getEmittedBin();
+        test_step.dependOn(&main.step);
+    }
+}
diff --git a/test/standalone/empty_global_error_set/main.zig b/test/standalone/empty_global_error_set/main.zig
new file mode 100644
index 0000000000..ecf7cf5167
--- /dev/null
+++ b/test/standalone/empty_global_error_set/main.zig
@@ -0,0 +1,4 @@
+fn errorName(err: anyerror) [:0]const u8 {
+    return @errorName(err);
+}
+export const error_name: *const anyopaque = &errorName;