Re: SIGILL when CPUTYPE set to anyting witjh avx and CFLAGS -O2

On 12/29/23 21:20, Konstantin Belousov wrote:
> On Fri, Dec 29, 2023 at 09:12:35PM +0100, Harry Schmalzbauer wrote:
>> On 12/29/23 18:00, Dimitry Andric wrote:
>>> On 29 Dec 2023, at 11:14, Harry Schmalzbauer <freebsd@omnilan.de> wrote:
>>>>
>>>> at least since 14-release, I can't compile base/ports with CPUTYPE post nehalem.  Any '-march' declaring AVX(*) capability leads to SIGILLing binaries with default -O2 CFLAGS.
>> ..
>>>>
>>>> If I compile without CFLAGS -O2 ("CFLAGS= -pipe"), -march=skylake-avx512 the binary doens't crash with SIGILL.
>>>>
>>>> Is CPUTYPE supposed to stay untouched these days?
>>>
>>> Obviously not, but are you sure your target CPU is correct? If it is not, the compiler may insert unsupported instructions.
>>
>> Ho Dimitry,  thanks for your attention!
>> I have to admit that I know much too less about contemporary compilers and
>> CPUs likewise, but target CPU matches -march ;-)
>> I nailed it down to AVX instructions.  Starting with 'sandybridge', Intel
>> CPUs provide avx instruction units, and starting with CPUTYPE?=sandybridge,
>> binaries crash on stable/14 (and late 14-current) on the corresponding
>> machines.  But only in combination with CFLAGS -O2!
>>
>>
>>> In any case, for the above gdb session, try the command "disassemble" to see which particular instruction it crashed on. That may give more information.
>>
>> Thanks for the hint!
>> This came out:
>> Program terminated with signal SIGILL, Illegal instruction.
>> Privileged opcode.
>> #0  0x000000000041e040 in init_yank ()
>> (gdb) disassemble
>> Dump of assembler code for function init_yank:
>>     0x000000000041e030 <+0>:	push   %rbp
>>     0x000000000041e031 <+1>:	mov    %rsp,%rbp
>>     0x000000000041e034 <+4>:	vpxor  %xmm0,%xmm0,%xmm0
>>     0x000000000041e038 <+8>:	vmovdqa -0x202c10(%rip),%xmm1        # 0x21b430
>> => 0x000000000041e040 <+16>:	kxnorw %k0,%k0,%k1
> This is AVX512 instruction (some of it subset, probably F), not AVX.
> 
...

>> Intel(R) Xeon(R) CPU E3-1275 v6 @ 3.80GHz (3800.00-MHz K8-class CPU)

My bad, sorry.
Confused machines.  This indeed was wrong target CPU, stupid me.
Previously I tested tih CPUTYPE?=haswell, which editors/vim survives 
currently.
Will run a base build with CPUTYPE?=haswell over the weekend and report 
back.
Sorry for the noise so far...

-harry