Re: Illegal instruction reported by qemu-ppc with -cpu 7400

[Matheus K. Ferst]

On 12/03/2022 23:51, Khem Raj wrote:
> Hi All
>
> I have built an app with musl C library for ppc32 using clang 14.0.0
> and I am using -mcpu=7400 to compile the whole thing including musl.
> This fails to run on qemu usermode reporting illegal instruction, a
> bit of digging revealed that it's caused by opcode in strspn()
> function from musl where clang is emitting vxor instruction and that's
> where qemu ppc bails out.
>
> Here is asm file generated by clang
>
> https://paste.debian.net/1233982/
>
> gcc ( 11.2 )
>
> https://paste.debian.net/1233983/
>
> As you can see the disassembly for gcc does not have vxor or any other
> altivec instructions in it.
> When I add -mno-altivec to clang then the issue is gone or when I use
> -mcpu=power5 the issue is gone too.
>
> This is preprocessed strspn.i
> https://paste.debian.net/1233987/
>
> I wonder if qemu-ppc -mcpu 7400 should have understood vxor instruction or not ?

Hi Khem,

A quick test suggests that vxor is working with -cpu 7400:
$ cat > vxor.c << EOF
int main(void)
{
    asm volatile ("vxor 2, 2, 2\n\t" ::: "v2");
    return 0;
}
EOF
$ powerpc64-linux-gnu-gcc -m32 -mcpu=7400 vxor.c -o vxor -static
$ qemu-ppc -cpu 7400 vxor
$ echo $?
0

Can you show us the command line you used? What version of QEMU are you 
running?

--
Matheus K. Ferst
Instituto de Pesquisas ELDORADO <http://www.eldorado.org.br/>
Analista de Software
Aviso Legal - Disclaimer <https://www.eldorado.org.br/disclaimer.html>