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Re: multiboot information structure flags are confusing me


From: Alex Thiel
Subject: Re: multiboot information structure flags are confusing me
Date: Wed, 13 Feb 2002 12:22:43 +0100

On Tuesday 12 February 2002 04:02, Timmy Douglas wrote:
> i want to enable some flags for the multiboot information
> structure. so i can get some VBE info.
>
> however, the docs talk about two separate groups of flags: the ones in
> the binary header and the multiboot info flags. it says that the
> multiboot info pointer is passed in %ebx (or whatever) to the main
> function, but how can i set the flags so grub can put what i want in
> the structure?
>

There are indeed two sets of flags: the OS requests features via the header 
in the OS image (see chapter OS image format in the multiboot documentation), 
and GRUB passes information about the actual state of the system in the 
multiboot info structure.

For example, the OS requests VBE information via bit 2 of the flags field in 
the OS header. Suppose the BIOS did not support VBE, then GRUB would set the 
corresponding flag in the multiboot info structure to zero and leave it to 
the application to handle the situation.

Cheers,

        Alex



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