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. Jan
