On Thu, Mar 30, 2023 at 08:24:20AM +0200, Jan Beulich wrote: > On 29.03.2023 18:29, Roger Pau Monné wrote: > > On Mon, Dec 05, 2022 at 04:10:28PM +0100, Jan Beulich wrote: > >> On 23.11.2022 16:45, Roger Pau Monne wrote: > >>> @@ -265,6 +266,15 @@ __efi64_mb2_start: > >>> cmpl $MULTIBOOT2_TAG_TYPE_END,MB2_tag_type(%rcx) > >>> je .Lrun_bs > >>> > >>> + /* > >>> + * Get command line from Multiboot2 information. > >>> + * Must be last parsed tag. > >> > >> Why? And how do you guarantee this? > > > > I think the comment is misleading, must be the last checked for tag in > > the loop that does this in assembly, because it's not using cmove. > > I've adjusted to: > > > > /* Get command line from Multiboot2 information. */ > > cmpl $MULTIBOOT2_TAG_TYPE_CMDLINE,MB2_tag_type(%rcx) > > jne .Lno_cmdline > > lea MB2_tag_string(%rcx),%rdx > > jmp .Lefi_mb2_next_tag > > .Lno_cmdline: > > > > Maybe there's some instruction I'm missing similar to a conditional > > lea? > > There isn't. If you want to get away without conditional branch, then > you'll need to LEA to a scratch register (unconditional) and then > CMOVcc from that scratch register.
Likely not worth it, unless you dislike the extra conditional branch. Thanks, Roger.
