image_scan(), image_scan_2(), image_scan_ext()

Arguments:

start

The address in memory from which to start scanning

end

The address in memory at which to stop scanning

docksum

image_scan_2() only. Set to 1 (one) to authenticate the image, or 0 (zero) to not authenticate the image. Default is 1: authenticate the image.

Description:

The image_scan() function scans memory for valid system images. As it scans memory, image_scan():

• Examines only the specified address range. If an OS image is outside the specified search range, image_scan() won't find that OS image.
• Looks on 4-byte boundaries for image header signatures (STARTUP_HDR_SIGNATURE).
• When it finds a signature, authenticates it.
• Verifies the checksums for the OS image and for the startup header.
• Copies the startup header from the image to a startup_header data structure (see “The startup header”).

The image_scan() function assumes that more than one bootable image may be present on the medium, and can compile a list of valid OS images in order to pick the most recent image and return this image's start address. In practice, however, because image_scan() scans only the range you specify with its start and end arguments, and you can specify a small range (e.g., 256 or 512 bytes) in the area on your media where the bootable image should be located, the function won't waste time looking for more than one image.

The image_scan_2() function assumes a single image, so it returns the start address of the first image it finds. It allows you to further reduce execution time by setting the docksum argument to 0 (zero) to skip image authentication.

Use the image_scan_ext() function for an x86 system with a BIOS. This function copies the startup code to memory from where it is stored using an industry-standard BIOS routine.

Returns:

≥0

Success: the start address of the (most recent) valid image found

-1

Failure