Jeremy Fitzhardinge <[EMAIL PROTECTED]> writes: > When the paravirt dispatcher gets run immediately on entry to > startup_32, the bss isn't cleared. This happens to work if the > hypervisor's domain builder loaded the complete kernel image and > cleared the bss for us, but this may not always be true (for example, > if we're running out of a decompressed bzImage). > > Change head.S so that it unconditionally clears the bss before doing > the paravirt dispatch or continuing on to normal native boot. > > There are a couple of points to note: > - We can't, in general, load the segment registers before paravirt > dispatch, because we could be running with a non-standard gdt and > segment selectors. In practice though, all code which ends up > jumping into startup_32 will have already set the segment registers > up to sane values, so we don't need to do it again. > - Paging may or may not be enabled, and if enabled we may or may not > be mapped to the proper kernel virtual address. To deal with this, > we compare the kernel's linked address with where we're actually > running, and use that to offset the bss pointer.
NAK. Skipping the segment register load is likely fine. Supporting V!=P at startup_32 is not. Assuming that we have a stack at startup_32 is not. If you want to figure out where the kernel is loaded you can do (from arch/i386/boot/head.S) > > /* Calculate the delta between where we were compiled to run > * at and where we were actually loaded at. This can only be done > * with a short local call on x86. Nothing else will tell us what > * address we are running at. The reserved chunk of the real-mode > * data at 0x34-0x3f are used as the stack for this calculation. > * Only 4 bytes are needed. > */ > leal 0x40(%esi), %esp > call 1f > 1: popl %ebp > subl $1b, %ebp > Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
