[romprefix] Do not preserve unused register %di

Since some PnP BIOSes fail to set %es:di to point to the PnP signature
on entry, we identify a PnP BIOS by scanning through the top 64kB of
base memory looking for the PnP structure.  We therefore don't
actually use the values of %es:di provided to the initialisation entry
point, and so there is no need to preserve them.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index ae18f05d038eb2b62fabfef0c16d335599b8d39c..99994401337ed6ca18cdb9360292cbde65ce80d7 100644 (file)
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -208,15 +208,8 @@ init:
        pushw   %cs
        popw    %ds
 
-       /* Shuffle some registers around.  We need %di available for
-        * the print_xxx functions, and in a register that's
-        * addressable from %es, so shuffle as follows:
-        *
-        *    %di (pointer to PnP structure) => %bx
-        *    %bx (runtime segment address, for PCI 3.0) => %gs
-        */
+       /* Store PCI 3.0 runtime segment address for later use */
        movw    %bx, %gs
-       movw    %di, %bx
 
        /* Store PCI bus:dev.fn address */
        movw    %ax, init_pci_busdevfn