On Thu, Sep 27, 2018 at 9:42 AM <xypr...@archlinux.org> wrote: > > From: Alexander F. Rødseth <xypr...@archlinux.org> > > Only ah needs to be set to 0 before calling interrupt 0x16 for waiting > for a keypress. > > This patch changes the line that uses xor so that it only zeroes "ah" instead > of "ax". > This saves a byte. > > Signed-off-by: Alexander F. Rødseth <xypr...@archlinux.org> > --- > arch/x86/boot/header.S | 11 ++++++----- > 1 file changed, 6 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S > index 850b8762e889..905cb96f43d4 100644 > --- a/arch/x86/boot/header.S > +++ b/arch/x86/boot/header.S > @@ -71,14 +71,15 @@ msg_loop: > jmp msg_loop > > bs_die: > - # Allow the user to press a key, then reboot > - xorw %ax, %ax > + # Allow the user to press a key > + xorb %ah, %ah
Because this is code running in 16-bit real mode, xorw does not need a 16-bit prefix and only uses 2 bytes. You save nothing by using xorb. -- Brian Gerst
