GCC and systemd teams: I compiled systemd-241 and expressly set march=winchip-c6 (an i486 class cpu). It generated illegal instructions (rdrand) in the code. Oddly, it does NOT do this when I set march=i486: Dump of assembler code for function rdrand: 0xb7e21440 <+0>: push %esi 0xb7e21441 <+1>: push %ebx 0xb7e21442 <+2>: call 0xb7e0af5d <__x86.get_pc_thunk.si> 0xb7e21447 <+7>: add $0x1acb39,%esi 0xb7e2144d <+13>: mov 0x2870(%esi),%ecx 0xb7e21453 <+19>: test %ecx,%ecx 0xb7e21455 <+21>: js 0xb7e21480 <rdrand+64> 0xb7e21457 <+23>: test %ecx,%ecx 0xb7e21459 <+25>: je 0xb7e214e0 <rdrand+160> 0xb7e2145f <+31>: rdrand %ecx <------ bad opcode 0xb7e21462 <+34>: setb %al 0xb7e21465 <+37>: mov 0xc(%esp),%edx 0xb7e21469 <+41>: mov %ecx,(%edx) 0xb7e2146b <+43>: cmp $0x1,%al 0xb7e2146d <+45>: sbb %eax,%eax 0xb7e2146f <+47>: and $0xfffffff5,%eax 0xb7e21472 <+50>: pop %ebx 0xb7e21473 <+51>: pop %esi 0xb7e21474 <+52>: ret ... It sure looks like systemd-v241 is trying to detect support for this instruction before using it: https://github.com/systemd/systemd/blob/v241/src/basic/random-util.c#L36 I confirmed that the processor does NOT report support for the rdrand instruction : # cpuid CPU 0: vendor_id = "CentaurHauls" version information (1/eax): processor type = primary processor (0) family = Intel Pentium, AMD K5/K6, Cyrix M1, NexGen Nx586, Centaur C6, Rise mP6, Transmeta Crusoe (5) model = 0x8 (8) stepping id = 0x5 (5) extended family = 0x0 (0) extended model = 0x0 (0) (simple synth) = VIA WinChip 2 (C6-2) miscellaneous (1/ebx): process local APIC physical ID = 0x0 (0) cpu count = 0x0 (0) CLFLUSH line size = 0x0 (0) brand index = 0x0 (0) brand id = 0x00 (0): unknown feature information (1/edx): x87 FPU on chip = true virtual-8086 mode enhancement = false debugging extensions = true page size extensions = false time stamp counter = true RDMSR and WRMSR support = true physical address extensions = false machine check exception = true CMPXCHG8B inst. = true APIC on chip = false SYSENTER and SYSEXIT = false memory type range registers = false PTE global bit = false machine check architecture = false conditional move/compare instruction = false page attribute table = false page size extension = false processor serial number = false CLFLUSH instruction = false debug store = false thermal monitor and clock ctrl = false MMX Technology = true FXSAVE/FXRSTOR = false SSE extensions = false SSE2 extensions = false self snoop = false hyper-threading / multi-core supported = false therm. monitor = false IA64 = false pending break event = false feature information (1/ecx): PNI/SSE3: Prescott New Instructions = false PCLMULDQ instruction = false 64-bit debug store = false MONITOR/MWAIT = false CPL-qualified debug store = false VMX: virtual machine extensions = false SMX: safer mode extensions = false Enhanced Intel SpeedStep Technology = false thermal monitor 2 = false SSSE3 extensions = false context ID: adaptive or shared L1 data = false FMA instruction = false CMPXCHG16B instruction = false xTPR disable = false perfmon and debug = false process context identifiers = false direct cache access = false SSE4.1 extensions = false SSE4.2 extensions = false extended xAPIC support = false MOVBE instruction = false POPCNT instruction = false time stamp counter deadline = false AES instruction = false XSAVE/XSTOR states = false OS-enabled XSAVE/XSTOR = false AVX: advanced vector extensions = false F16C half-precision convert instruction = false RDRAND instruction = false <------- NOT SUPPORTED hypervisor guest status = false extended processor signature (0x80000001/eax): generation = 0x5 (5) model = 0x8 (8) stepping = 0x5 (5) (simple synth) = unknown extended feature flags (0x80000001/edx): x87 FPU on chip = true virtual-8086 mode enhancement = false debugging extensions = true page size extensions = false time stamp counter = true RDMSR and WRMSR support = true physical address extensions = false machine check exception = true CMPXCHG8B inst. = true APIC on chip = false SYSCALL and SYSRET instructions = false memory type range registers = false global paging extension = false machine check architecture = false conditional move/compare instruction = false page attribute table = false page size extension = false multiprocessing capable = false AMD multimedia instruction extensions = false MMX Technology = true extended MMX = false SSE extensions = false AA-64 = false 3DNow! instruction extensions = false 3DNow! instructions = true brand = "IDT WinChip 2-3D" L1 TLB/cache information: 2M/4M pages & L1 TLB (0x80000005/eax): instruction # entries = 0x5 (5) instruction associativity = 0x0 (0) data # entries = 0x0 (0) data associativity = 0x80 (128) L1 TLB/cache information: 4K pages & L1 TLB (0x80000005/ebx): instruction # entries = 0x80 (128) instruction associativity = 0x8 (8) data # entries = 0x80 (128) data associativity = 0x8 (8) L1 data cache information (0x80000005/ecx): line size (bytes) = 0x20 (32) lines per tag = 0x1 (1) associativity = 0x4 (4) size (KB) = 0x20 (32) L1 instruction cache information (0x80000005/edx): line size (bytes) = 0x20 (32) lines per tag = 0x1 (1) associativity = 0x2 (2) size (KB) = 0x20 (32) 0xc0000001 0x00: eax=0x00000585 extended feature flags (0xc0000001/edx): alternate instruction set = true alternate instruction set enabled = false random number generator = true random number generator enabled = false LongHaul MSR 0000_110Ah = true FEMMS = true advanced cryptography engine (ACE) = false advanced cryptography engine (ACE)enabled = true montgomery multiplier/hash (ACE2) = true montgomery multiplier/hash (ACE2) enabled = false padlock hash engine (PHE) = false padlock hash engine (PHE) enabled = false padlock montgomery mult. (PMM) = false padlock montgomery mult. (PMM) enabled = false VIA C7 Temperature/Voltage Sensors (0xc0000002): core temperature (degrees C) = 0x44 (68) input voltage (mV) = 2092 (0x57) 0xc0000002 0x00: ebx=0x436e6957 ecx=0x20706968 edx=0x44332d32 0xc0000003 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 0xc0000004 0x00: eax=0x00000000 ebx=0x00000000 ecx=0x00000000 edx=0x00000000 0xc0000005 0x00: eax=0xc0000005 ebx=0x08800880 ecx=0x20040120 edx=0x20020120 (multi-processing synth): none (multi-processing method): Generic leaf 1 no multi-threading (synth) = VIA WinChip 2 (C6-2) - Matthew
