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+.. SPDX-License-Identifier: GPL-2.0+
+
+.. index::
+   single: cpuid (command)
+
+cpuid command
+=============
+
+Synopsis
+--------
+
+::
+
+    cpuid <op>
+
+Description
+-----------
+
+The cpuid command requests CPU-identification information on x86 CPUs. The
+operation <op> selects what information is returned. Up to four 32-bit registers
+can be update (eax-edx) depending on the operation.
+
+Configuration
+-------------
+
+The cpuid command is only available on x86.
+
+Return value
+------------
+
+The return value $? is 0 (true).
+
+Example
+-------
+
+::
+
+    => cpuid 1
+    eax 00060fb1
+    ebx 00040800
+    ecx 80002001
+    edx 178bfbfd
+
+This shows checking for 64-bit 'long' mode::
+
+    => cpuid 80000000
+    eax 8000000a
+    ebx 68747541
+    ecx 444d4163
+    edx 69746e65
+    => cpuid 80000001
+    eax 00060fb1
+    ebx 00000000
+    ecx 00000007
+    edx 2193fbfd   # Bit 29 is set in edx, so long mode is available
+
+On a 32-bit-only CPU::
+
+    => cpuid 80000000
+    eax 80000004
+    ebx 756e6547
+    ecx 6c65746e
+    edx 49656e69
+    => cpuid 80000001
+    eax 00000663
+    ebx 00000000
+    ecx 00000000
+    edx 00000000   # Bit 29 is not set in edx, so long mode is not available