Is GET_CR0_INTO_EAX macro unused?

From: Denys Vlasenko
Date: Mon Oct 02 2017 - 08:36:45 EST

Hi Andy,

From by git archaeology, looks like last use of GET_CR0_INTO_EAX
was removed long ago, in 2008 (see commit below).

Right now, I only grep it here in a comment in entry_32.S:
* We use macros for low-level operations which need to be overridden
* for paravirtualization. The following will never clobber any registers:
* INTERRUPT_RETURN (aka. "iret")
* GET_CR0_INTO_EAX (aka. "movl %cr0, %eax")

To support GET_CR0_INTO_EAX, paravirt has PV_CPU_read_cr0 a.k.a.
struct pv_cpu_ops::read_cr0 and a bunch of code to support it
for each hypervisor.

Can we delete it?
Or am I missing a non-obvious place where this macro is still in use?

commit 7643e9b936b4af31ba4851eb7d5b3a3bfad52502
Author: Alexander van Heukelum <heukelum@xxxxxxxxxxx>
Date: Tue Sep 9 21:56:02 2008 +0200

i386: convert hardware exception 7 to an interrupt gate

Handle no coprocessor exception with interrupt initially off.

device_not_available in entry_32.S calls either math_state_restore
or math_emulate. This patch adds an extra indirection to be
able to re-enable interrupts explicitly in traps_32.c

Signed-off-by: Alexander van Heukelum <heukelum@xxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 109792b..5a88585 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -760,20 +760,9 @@ ENTRY(device_not_available)
pushl $-1 # mark this as an int
- testl $0x4, %eax # EM (math emulation bit)
- jne device_not_available_emulate
- preempt_stop(CLBR_ANY)
- call math_state_restore
- jmp ret_from_exception
- pushl $0 # temporary storage for ORIG_EIP
+ pushl $do_device_not_available
- call math_emulate
- addl $4, %esp
- jmp ret_from_exception
+ jmp error_code