linux-kernel - lguest: bug in lg_irq

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Message-ID: <CAK1hOcMg328+Jd9cgnpToKknDUa47Sz-cwBaLVKiya33JwUXNw@mail.gmail.com>
Date:	Thu, 26 Feb 2015 16:39:54 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: lguest: bug in lg_irq_enable?

ENTRY(lg_irq_enable)
        /*
         * The reverse of irq_disable, this sets lguest_data.irq_enabled to
         * X86_EFLAGS_IF (ie. "Interrupts enabled").
         */
        movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled
        /*
         * But now we need to check if the Host wants to know: there might have
         * been interrupts waiting to be delivered, in which case it will have
         * set lguest_data.irq_pending to X86_EFLAGS_IF.  If it's not zero, we
         * jump to send_interrupts, otherwise we're done.
         */
        testl $0, lguest_data+LGUEST_DATA_irq_pending
^^^^^^^^^^^^^^^^^??????????
        jnz send_interrupts
        /*
         * One cool thing about x86 is that you can do many things without using
         * a register.  In this case, the normal path hasn't needed to save or
         * restore any registers at all!
         */
        ret
send_interrupts:


TEST with zero will always set ZF. Thus, "jnz send_interrupts" never jumps.

-- 
vda
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