From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir@xen.org>
Subject: Re: [PATCH] x86: slightly improve stack trace on debug
 builds
Date: Tue, 25 Sep 2012 16:48:59 +0100
Message-ID: <CC8790FB.4CD98%keir@xen.org>
References: <5061E4CF020000780009DB98@nat28.tlf.novell.com>
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To: Jan Beulich <JBeulich@suse.com>, xen-devel <xen-devel@lists.xen.org>
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On 25/09/2012 16:07, "Jan Beulich" <JBeulich@suse.com> wrote:

> +    addr = regs->eip;
> +    while ( !is_kernel_text(addr) &&
> +            (system_state > SYS_STATE_boot || !is_kernel_inittext(addr)) )
> +    {
> +        /* Special case when a bad pointer was called. */
> +        addr ^= regs->eip ^ *ESP_BEFORE_EXCEPTION(regs);
> +        if ( addr == regs->eip )
> +            break;
> +    }

Lol, how does your brain work this way? It took me 15 minutes to decode this
to something like (also I added range checks on ESP_BEFORE_EXCEPTION(regs),
what do you think?):

bool_t is_current_kernel_text(unsigned long addr)
{
    return (is_kernel_text(addr) ||
            (system_state == SYS_STATE_boot && is_kernel_inittext(addr)));
}

...

/*
 * If RIP is not valid hypervisor code then someone may have called into
 * oblivion. Peek to see if they left a return address at top of stack.
 */
addr = (!is_current_kernel_text(regs->eip) &&
        (ESP_BEFORE_EXCEPTION(regs) >= low) &&
        (ESP_BEFORE_EXCEPTION(regs) < high) &&
        is_current_kernel_text(*ESP_BEFORE_EXCEPTION(regs)))
       ? *ESP_BEFORE_EXCEPTION(regs) : regs->eip;