ia32 emulation on Pentium I

ia32 emulation on Pentium I

[Dmitry Mikushin]

Dear all,

I'm trying to enable ia32 emulation in k1om kernel. Linux kernel is
ported for k1om, but with ia32 emulation disabled. With it enabled,
I'm getting the following error:

LD arch/x86/crypto/built-in.o
AS arch/x86/ia32/ia32entry.o
arch/x86/ia32/ia32entry.S: Assembler messages:
arch/x86/ia32/ia32entry.S:192: Error: `sysexit' is not supported on `k1om'
make[2]: *** [arch/x86/ia32/ia32entry.o] Error 1
make[1]: *** [arch/x86/ia32] Error 2
make: *** [arch/x86] Error 2

sysexit is not supported because k1om (Intel MIC) is essentially Pentium
I with AVX512 extensions.

sysexit is used in macro ENABLE_INTERRUPTS_SYSEXIT32, which is in turn
used in ENTRY(ia32_sysenter_target).

So, it seems ia32 emulation assumes Pentium II+. Do you see a quick
way to make it Pentium I -compatible?

Thanks,
- D.

Re: ia32 emulation on Pentium I

[Andi Kleen]

Dmitry Mikushin <dmitry@kernelgen.org> writes:
>
> So, it seems ia32 emulation assumes Pentium II+. Do you see a quick
> way to make it Pentium I -compatible?

The SYSENTER code path should be never executed, so you could either hack the
assembler to allow it, or just open code it.

Something like (totally untested):

From: Andi Kleen <ak@linux.intel.com>

use .byte to implement SYSEXIT for k1om assembler

diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
index bba3cf8..1ad2378 100644
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -130,6 +130,8 @@ static inline notrace unsigned long arch_local_irq_save(void)
 #define PARAVIRT_ADJUST_EXCEPTION_FRAME	/*  */
 
 #define INTERRUPT_RETURN	iretq
+#define SYSEXIT			.byte 0x0f,0x35
+
 #define USERGS_SYSRET64				\
 	swapgs;					\
 	sysretq;
@@ -139,7 +141,7 @@ static inline notrace unsigned long arch_local_irq_save(void)
 #define ENABLE_INTERRUPTS_SYSEXIT32		\
 	swapgs;					\
 	sti;					\
-	sysexit
+	SYSEXIT	
 
 #else
 #define INTERRUPT_RETURN		iret

-- 
ak@linux.intel.com -- Speaking for myself only