On 01.08.2023 01:37, Shawn Anastasio wrote: > On 7/31/23 10:46 AM, Jan Beulich wrote: >> On 29.07.2023 00:21, Shawn Anastasio wrote: >>> + /* If we're at the correct address, skip copy */ >>> + cmpld %r1, %r12 >>> + beq .L_correct_address >> >> Can this ever be the case, especially with the MMU-off behavior you >> describe in the comment above? Wouldn't you need to ignore the top >> four bits in the comparison? > > It will always be the case after the code jumps to XEN_VIRT_START after > the copy takes place.
Well, of course. > I could have it jump past the copy loop entirely, > but then I'd need to duplicate the TOC setup. I don't think I understand this part of your reply: .L_correct_address _is_ past the copy loop. >>> + /* Copy bytes until _end */ >>> + LOAD_REG_ADDR(%r11, _end) >>> + addi %r1, %r1, -8 >>> + li %r13, -8 >>> +.L_copy_xen: >>> + ldu %r10, 8(%r1) >>> + stdu %r10, 8(%r13) >>> + cmpld %r1, %r11 >>> + blt .L_copy_xen >>> + >>> + /* Jump to XEN_VIRT_START */ >>> + mtctr %r12 >>> + bctr >>> +.L_correct_address: >> >> Can the two regions potentially overlap? Looking at the ELF header >> it's not clear to me what guarantees there are that this can't >> happen. > > As I understand it, any bootloader that placed the kernel at a low > enough address for this to be an issue wouldn't be able to boot Linux or > FreeBSD, so in practice it's a safe bet that this won't be the case. Fair enough then. Jan
