bugGNU GRUB - Bugs: bug #59240, Enumerating VBE modes can abort...

 
 

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bug #59240: Enumerating VBE modes can abort halfway through

Submitted by:  <qwertial>
Submitted on:  Fri 09 Oct 2020 08:18:13 AM UTC  
 
Category:  User Interface Severity:  Major
Priority:  5 - Normal Item Group:  None
Status:  None Privacy:  Public
Assigned to:  None Originator Name: 
Open/Closed:  Open Release: 
Release:  Git master Reproducibility:  Every Time
Planned Release:  None

Fri 09 Oct 2020 08:18:13 AM UTC, original submission:  

grub-core/video/i386/vbe.c:

  for (p = vbe_mode_list; *p != 0xFFFF; p++)
    {
      grub_vbe_get_video_mode_info (*p, &vbe_mode_info);
      if (grub_errno != GRUB_ERR_NONE)
        {
          /* Could not retrieve mode info, retreat.  */
          grub_errno = GRUB_ERR_NONE;
          break;
        }

      vbe2videoinfo (*p, &vbe_mode_info, &mode_info);
      if (hook (&mode_info, hook_arg))
        return 1;
    }
  return 0;

The break should have been a continue. Otherwise, GRUB will stop enumerating VBE modes as soon as one 0x4f01 call returns failure. I happen to have a video BIOS where the very first mode in the list returned from 0x4f00 (and a number of modes that follow) does not actually work, but the video BIOS is otherwise fully functional.

RBIL warns against this very situation in the entry covering the 0x4f00 call:

> not all of the video modes in the list of mode numbers may be
>   supported, e.g. if they require more memory than currently installed
>   or are not supported by the attached monitor.  Check any mode you
>   intend to use through AX=4F01h first.


So it should be expected that some modes may fail to work, but that has no bearing on whether any subsequent modes will.

<qwertial>

 

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