From 5ee0c6422399b5219dbc06a3d7bb9f59f20cf7ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Sun, 16 Aug 2026 07:25:03 +0200
Subject: [PATCH] std.zig.system.x86: deal with lying hypervisors

closes https://codeberg.org/ziglang/zig/issues/36515
---
 lib/std/zig/system/x86.zig | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/std/zig/system/x86.zig b/lib/std/zig/system/x86.zig
index e4fa035747ce7195a1401722d1a9aa366dfd9698..23687255a5be522c3c0f5bb7579df484e7e45277 100644
--- a/lib/std/zig/system/x86.zig
+++ b/lib/std/zig/system/x86.zig
@@ -76,7 +76,13 @@ pub fn detectNativeCpuAndFeatures(arch: Target.Cpu.Arch, os: Target.Os, query: T
             0x756e6547 => detectIntelProcessor(&cpu, family, model, brand_id),
             0x68747541 => detectAmdProcessor(&cpu, family, model),
             else => null,
-        }) |m| {
+        }) |m| b: {
+            // Some hypervisors are evil liars and will operate in long mode while identifying as a
+            // CPU model that never had long mode in reality. We've seen this in practice with
+            // athlon_xp (AMD K7). Catch this contradiction and fall back to using a generic CPU
+            // model with the features we detected earlier.
+            if (cpu.has(.x86, .@"64bit") and !Target.x86.featureSetHas(m.features, .@"64bit")) break :b;
+
             cpu.model = m;
         }
     }
-- 
2.54.0