[PATCH v2] ARM: entry: omit FP emulation for UND exceptions taken in kernel mode

[Dmitry Osipenko]

18.11.2020 16:08, Ard Biesheuvel пишет:
> diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
> index c4220f51fcf3..0ea8529a4872 100644
> --- a/arch/arm/kernel/entry-armv.S
> +++ b/arch/arm/kernel/entry-armv.S
> @@ -252,31 +252,10 @@ __und_svc:
>  #else
>  	svc_entry
>  #endif
> -	@
> -	@ call emulation code, which returns using r9 if it has emulated
> -	@ the instruction, or the more conventional lr if we are to treat
> -	@ this as a real undefined instruction
> -	@
> -	@  r0 - instruction
> -	@
> -#ifndef CONFIG_THUMB2_KERNEL
> -	ldr	r0, [r4, #-4]
> -#else
> -	mov	r1, #2
> -	ldrh	r0, [r4, #-2]			@ Thumb instruction at LR - 2
> -	cmp	r0, #0xe800			@ 32-bit instruction if xx >= 0
> -	blo	__und_svc_fault
> -	ldrh	r9, [r4]			@ bottom 16 bits
> -	add	r4, r4, #2
> -	str	r4, [sp, #S_PC]
> -	orr	r0, r9, r0, lsl #16
> -#endif
> -	badr	r9, __und_svc_finish
> -	mov	r2, r4
> -	bl	call_fpe
>  
>  	mov	r1, #4				@ PC correction to apply
> -__und_svc_fault:
> + THUMB(	tst	r5, #PSR_T_BIT		)	@ exception taken in Thumb mode?
> + THUMB(	movne	r1, #2			)	@ if so, fix up PC correction
>  	mov	r0, sp				@ struct pt_regs *regs
>  	bl	__und_fault

Am I understanding correctly that when call_fpe was invoked previously,
it was supposed to print extra debug info about the VFP state? But it
didn't work properly for thumb mode, correct?