Date: Tue, 24 Jul 2001 16:45:11 -0500 From: Bob Van Valzah <Bob@Talarian.Com> To: John Baldwin <jhb@FreeBSD.org> Cc: FreeBSD-Mobile@FreeBSD.org, Doug Ambrisko <ambrisko@ambrisko.com> Subject: Re: ThinkPad 600X: Can't work out which disk we are booting from Message-ID: <3B5DEC67.3060204@Talarian.Com> References: <XFMail.010724143824.jhb@FreeBSD.org>
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Ok, that's kind of what I thought.
So how about from the "top down"? I don't know what sort of pseudo ops
and expression evaluation this assembler has, but I remember once doing
an expression that'd find the first address past the end of a block and
then subtracting the size of the jmp so I could .org up there leaving a
variable-sized gap at the end. That sort of thing might work unless
you're right up against the wall on space.
But I can also see where it might be tricky to detect a block overflow
with this kind of scheme.
Bob
John Baldwin wrote:
>On 24-Jul-01 Bob Van Valzah wrote:
>
>>Doug, Glad you're aware of the problem and have already formulated a fix.
>>
>>John, I agree that the header file approach might be cleaner.
>>
>>But here's another idea: Could the "jmp main" at the start of boot1.s be
>>followed immediately by a "jmp xread"? This'd create a sort of entry
>>point table at the start of boot1 that could be used by boot2 without
>>fear of things moving around. But I have to say that I haven't written
>>any substantial amounts of assembler since the 8080 days (dating myself
>>there) and I've never looked at the x86 boot sequence, so I may be way
>>out of my league with this suggestion.
>>
>
>Unfortunately, the BPB needs to be at a fixed offset and there isn't sufficient
>room for another jmp at offset 0x4.
>
>
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Ok, that's kind of what I thought.<br>
<br>
So how about from the "top down"? I don't know what sort of pseudo ops and
expression evaluation this assembler has, but I remember once doing an expression
that'd find the first address past the end of a block and then subtracting
the size of the jmp so I could .org up there leaving a variable-sized gap
at the end. That sort of thing might work unless you're right up against
the wall on space.<br>
<br>
But I can also see where it might be tricky to detect a block overflow with
this kind of scheme.<br>
<br>
Bob<br>
<br>
John Baldwin wrote:<br>
<blockquote type="cite" cite="mid:XFMail.010724143824.jhb@FreeBSD.org">
<pre wrap="">On 24-Jul-01 Bob Van Valzah wrote:<br></pre>
<blockquote type="cite">
<pre wrap="">Doug, Glad you're aware of the problem and have already formulated a fix.<br><br>John, I agree that the header file approach might be cleaner.<br><br>But here's another idea: Could the "jmp main" at the start of boot1.s be <br>followed immediately by a "jmp xread"? This'd create a sort of entry <br>point table at the start of boot1 that could be used by boot2 without <br>fear of things moving around. But I have to say that I haven't written <br>any substantial amounts of assembler since the 8080 days (dating myself <br>there) and I've never looked at the x86 boot sequence, so I may be way <br>out of my league with this suggestion.<br></pre>
</blockquote>
<pre wrap=""><!----><br>Unfortunately, the BPB needs to be at a fixed offset and there isn't sufficient<br>room for another jmp at offset 0x4.<br> <br></pre>
</blockquote>
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