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The command line option `no387' is designed to disable the FPU
entirely. This only 'works' with CONFIG_MATH_EMULATION enabled.
But on 64bit this cannot work because user space expects SSE to work which
required basic FPU support. MATH_EMULATION does not help because SSE is not
emulated.
The command line option `nofxsr' should also be limited to 32bit because
FXSR is part of the required flags on 64bit so turning it off is not
possible.
Clearing X86_FEATURE_FPU without emulation enabled will not work anyway and
hang in fpu__init_system_early_generic() before the console is enabled.
Setting additioal dependencies, ensures that the CPU still boots on a
modern CPU. Otherwise, dropping FPU will leave FXSR enabled causing the
kernel to crash early in fpu__init_system_mxcsr().
With XSAVE support it will crash in fpu__init_cpu_xstate(). The problem is
that xsetbv() with XMM set and SSE cleared is not allowed. That means
XSAVE has to be disabled. The XSAVE support is disabled in
fpu__init_system_xstate_size_legacy() but it is too late. It can be
removed, it has been added in commit
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.. | ||
mce | ||
microcode | ||
mtrr | ||
resctrl | ||
.gitignore | ||
amd.c | ||
aperfmperf.c | ||
bugs.c | ||
cacheinfo.c | ||
centaur.c | ||
common.c | ||
cpu.h | ||
cpuid-deps.c | ||
cyrix.c | ||
hygon.c | ||
hypervisor.c | ||
intel.c | ||
intel_epb.c | ||
intel_pconfig.c | ||
Makefile | ||
match.c | ||
mkcapflags.sh | ||
mshyperv.c | ||
perfctr-watchdog.c | ||
powerflags.c | ||
proc.c | ||
rdrand.c | ||
scattered.c | ||
topology.c | ||
transmeta.c | ||
umc.c | ||
vmware.c |