Re: [PATCH 5.0 30/46] x86/boot/compressed/64: Do not read legacy ROM on EFI system

On Sat, Mar 09, 2019 at 10:10:19PM -0800, hpa@zytor.com wrote:

...

@@ -47,8 +50,18 @@ static unsigned long find_trampoline_pla * This code is based on reserve_bios_regions(). */

• ebda_start = *(unsigned short *)0x40e << 4;
• bios_start = *(unsigned short *)0x413 << 10;

• /*

• * EFI systems may not provide legacy ROM. The memory may not be
  

mapped

• * at all.
  

• *
  

• * Only look for values in the legacy ROM for non-EFI system.
  

• */
  

• signature = (char *)&boot_params->efi_info.efi_loader_signature;

• if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&

•    strncmp(signature, EFI64_LOADER_SIGNATURE, 4)) {
  

• ebda_start = *(unsigned short *)0x40e << 4;
  

• bios_start = *(unsigned short *)0x413 << 10;
  

• }

  if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX) bios_start = BIOS_START_MAX;

Only one objection: the explanation is nonsensical.

Well, that's the best explanation I've come up with :/

I would be glad for any insight here.