Re: [PATCH][RESEND] x86_emulator: Emulate cld and std instruction

[Avi Kivity <avi@qumranet.com>]

Mohammed Gamal wrote:
> This patch adds 'cld' and 'std' instructions to the emulator
>
>   

I presume for big real mode?  Which guest wants it?

> @@ -1755,6 +1755,14 @@ special_insn:
>  		ctxt->eflags |= X86_EFLAGS_IF;
>  		c->dst.type = OP_NONE;	/* Disable writeback. */
>  		break;
> +	case 0xfc: /* cld */
> +		ctxt->eflags &= ~EFLG_DF;
> +		c->dst.type = OP_NONE;  /* Disable writeback. */
> +		break;
> +	case 0xfd: /* std */
> +		ctxt->eflags |= EFLG_DF;
> +		c->dst.type = OP_NONE;  /* Disable writeback. */
> +		break;
>   

You need to add non-zero entries in opcode_table[] for this to work.  
Also, why disable writeback?  If there is not DstSomething in 
opcode_table[], c->dst.type will be OP_NONE anyway.

I would like to see test cases for emulator changes.  See 
users/test/x86/emulator.c.  Of course, right now it is impossible to 
cause cld and std to execute in the emulator.  But with the proposed 
invalid_guest_state() change, it should be easy to to cause this state 
and force emulation.

So how about adding optional invalid_guest_state() support (controlled 
by a module parameter), then start adding instructions and test cases, 
then removing the module parameter when everything works?

-- 
error compiling committee.c: too many arguments to function