I'm trying to create a VM of a 486 without FPU, like the 80486SX. I figured this could be accomplished with QEMU. I couldn't find the possibility to directly specify such a cpu (there's only the option -cpu=486). Based on the documentation, I thought it would be possible to remove the FPU by specifying the cpu as follows
qemu-system-i386 -cpu 486,-fpu (...)
But after I installed Debian 5.0 (the last Debian to support the 486), cat/proc tells me that a FPU is indeed considered present (even though it's not in the flags), and gcc will emit floating point instructions for a simple hello-world style program printing doubles, and QEMU will happily execute it.
user@debian-486-nofpu:~/$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 4
model : 8
model name : 486 DX/4
stepping : 0
cache size : 0 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : no
cpuid level : 1
wp : yes
flags : pse
bogomips : 466.94
clflush size : 32
power management: