| Issue |
71226
|
| Summary |
Not all Skylake CPUs support AVX
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
clausecker
|
@blastwave reported `clang -march=native` (on clang 14.0.5 as shipped with FreeBSD) generating binaries that wouldn't work on the host they were compiled on. The CPU reports itself as (in FreeBSD's dmesg output):
```
CPU: Intel(R) Pentium(R) CPU G4500 @ 3.50GHz (3500.00-MHz K8-class CPU)
Origin="GenuineIntel" Id=0x506e3 Family=0x6 Model=0x5e Stepping=3
Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
Features2=0x4ffaebbf<SSE3,PCLMULQDQ,DTES64,MON,DS_CPL,VMX,EST,TM2,SSSE3,SDBG,CX16,xTPR,PDCM,PCID,SSE4.1,SSE4.2,x2APIC,MOVBE,POPCNT,TSCDLT,AESNI,XSAVE,OSXSAVE,RDRAND>
AMD Features=0x2c100800<SYSCALL,NX,Page1GB,RDTSCP,LM>
AMD Features2=0x121<LAHF,ABM,Prefetch>
Structured Extended Features=0x2942607<FSGSBASE,TSCADJ,SGX,ERMS,INVPCID,NFPUSG,RDSEED,SMAP,CLFLUSHOPT,PROCTRACE>
Structured Extended Features3=0xc000000<IBPB,STIBP>
XSAVE Features=0xf<XSAVEOPT,XSAVEC,XINUSE,XSAVES>
VT-x: PAT,HLT,MTF,PAUSE,EPT,UG,VPID
TSC: P-state invariant, performance statistics
```
This is a Skylake CPU without AVX support. Clang [detects](https://github.com/llvm/llvm-project/blob/284c6990c133ed88f32de111accacc9f55a7a51d/llvm/lib/TargetParser/Host.cpp#L767) it as type `skylake` and thus enables AVX, but that is not supported.
The following code, when compiled with `-march=native` triggers the bug:
```
#include <stdio.h>
int main()
{
printf("%f\n", 1.0);
}
```
Please fix the `-march=native` logic to take this possibility into account.
## Additional details
```
esther$ uname -apKU
FreeBSD esther 13.2-RELEASE-p4 FreeBSD 13.2-RELEASE-p4 GENERIC amd64 amd64 1302001 1302001
esther$ freebsd-version -kru
13.2-RELEASE-p4
13.2-RELEASE-p4
13.2-RELEASE-p4
esther$ sysctl hw.model
hw.model: Intel(R) Pentium(R) CPU G4500 @ 3.50GHz
esther$ cat foo.c
#include <stdio.h>
int main() {
printf("%f\n", 1.0);
return 0;
}
esther$ cc -std=iso9899:1999 -m64 -O3 -ffast-math -ffp-contract=on -march=native -mtune=native -mfma -S -o foo.s foo.c
esther$ cat foo.s
.text
.file "foo.c"
.section .rodata.cst8,"aM",@progbits,8
.p2align 3 # -- Begin function main
.LCPI0_0:
.quad 0x3ff0000000000000 # double 1
.text
.globl main
.p2align 4, 0x90
.type main,@function
main: # @main
.cfi_startproc
# %bb.0:
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset %rbp, -16
movq %rsp, %rbp
.cfi_def_cfa_register %rbp
vmovsd .LCPI0_0(%rip), %xmm0 # xmm0 = mem[0],zero
movl $.L.str, %edi
movb $1, %al
callq printf
xorl %eax, %eax
popq %rbp
.cfi_def_cfa %rsp, 8
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
.cfi_endproc
# -- End function
.type .L.str,@object # @.str
.section .rodata.str1.1,"aMS",@progbits,1
.L.str:
.asciz "%f\n"
.size .L.str, 4
.ident "FreeBSD clang version 14.0.5 (https://github.com/llvm/llvm-project.git llvmorg-14.0.5-0-gc12386ae247c)"
.section ".note.GNU-stack","",@progbits
.addrsig
esther$ cc -o foo foo.s
esther$ ./foo
Illegal instruction (core dumped)
```
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