[syslinux] [PATCH] isohybrid: Generate MBR even when in EFI mode

[Geert Stappers]

Full quote, no new text, just a reminder

On Wed, Feb 15, 2012 at 12:12:17PM -0500, Matthew Garrett wrote:
> Various EFI systems insist that there be no active flag in the pMBR in
> order to parse the GPT. The only way around this is to also generate a
> valid MBR - the firmware will then pick that up and use the system
> partition provided there. In order to deal with other EFI "sanity" checks,
> the partition type for the non-EFI partitions is set to 0 to skip the
> firmware bailing because of overlapping partitions.
> ---
>  utils/isohybrid.c |   54 ++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 files changed, 49 insertions(+), 5 deletions(-)
> 
> diff --git a/utils/isohybrid.c b/utils/isohybrid.c
> index 1dcbaa1..ac04bfd 100644
> --- a/utils/isohybrid.c
> +++ b/utils/isohybrid.c
> @@ -54,7 +54,7 @@ enum { VERBOSE = 1 , EFI = 2 , MAC = 4};
>  uint16_t head = 64;             /* 1 <= head <= 256 */
>  uint8_t sector = 32;            /* 1 <= sector <= 63  */
>  
> -uint8_t entry = 1;              /* partition number: 1 <= entry <= 4 */
> +uint8_t entry = 0;              /* partition number: 1 <= entry <= 4 */
>  uint8_t offset = 0;             /* partition offset: 0 <= offset <= 64 */
>  uint16_t type = 0x17;           /* partition type: 0 <= type <= 255 */
>  uint32_t id = 0;                /* MBR: 0 <= id <= 0xFFFFFFFF(4294967296) */
> @@ -300,6 +300,8 @@ check_option(int argc, char *argv[])
>              entry = strtoul(optarg, &err, 0);
>              if (entry < 1 || entry > 4)
>                  errx(1, "invalid entry: `%s', 1 <= entry <= 4", optarg);
> +	    if (mode & MAC || mode & EFI)
> +		errx(1, "setting an entry is unsupported with EFI or Mac");
>              break;
>  
>          case 'o':
> @@ -334,10 +336,14 @@ check_option(int argc, char *argv[])
>  
>  	case 'u':
>  	    mode |= EFI;
> +	    if (entry)
> +		errx(1, "setting an entry is unsupported with EFI or Mac");
>  	    break;
>  
>  	case 'm':
>  	    mode |= MAC;
> +	    if (entry)
> +		errx(1, "setting an entry is unsupported with EFI or Mac");
>  	    break;
>  
>          case 'v':
> @@ -581,6 +587,12 @@ initialise_mbr(uint8_t *mbr)
>  	memcpy(mbr, afp_header, sizeof(afp_header));
>      }
>  
> +    if (!entry)
> +	entry = 1;
> +
> +    if (mode & EFI)
> +	type = 0;
> +
>      mbr += MBRSIZE;                                 /* offset 432 */
>  
>      tmp = lendian_int(de_lba * 4);
> @@ -633,6 +645,40 @@ initialise_mbr(uint8_t *mbr)
>              tmp = lendian_int(psize);
>              memcpy(&mbr[12], &tmp, sizeof(tmp));
>          }
> +        if (i == 2 && (mode & EFI))
> +        {
> +            mbr[0] = 0x0;
> +            mbr[1] = 0xfe;
> +            mbr[2] = 0xff;
> +            mbr[3] = 0xff;
> +            mbr[4] = 0xef;
> +            mbr[5] = 0xfe;
> +            mbr[6] = 0xff;
> +            mbr[7] = 0xff;
> +
> +            tmp = lendian_int(efi_lba * 4);
> +            memcpy(&mbr[8], &tmp, sizeof(tmp));
> +
> +            tmp = lendian_int(efi_count);
> +            memcpy(&mbr[12], &tmp, sizeof(tmp));
> +        }
> +        if (i == 3 && (mode & MAC))
> +        {
> +            mbr[0] = 0x0;
> +            mbr[1] = 0xfe;
> +            mbr[2] = 0xff;
> +            mbr[3] = 0xff;
> +            mbr[4] = 0x0;
> +            mbr[5] = 0xfe;
> +            mbr[6] = 0xff;
> +            mbr[7] = 0xff;
> +
> +            tmp = lendian_int(mac_lba * 4);
> +            memcpy(&mbr[8], &tmp, sizeof(tmp));
> +
> +            tmp = lendian_int(mac_count);
> +            memcpy(&mbr[12], &tmp, sizeof(tmp));
> +        }
>          mbr += 16;
>      }
>      mbr[0] = 0x55;
> @@ -908,8 +954,7 @@ main(int argc, char *argv[])
>  	if (!read_efi_section(buf)) {
>  	    buf += 32;
>  	    if (!read_efi_catalogue(buf, &efi_count, &efi_lba) && efi_lba) {
> -		offset = 1;
> -		type = 0xee;
> +		offset = 0;
>  	    } else {
>  		errx(1, "%s: invalid efi catalogue", argv[0]);
>  	    }
> @@ -925,8 +970,7 @@ main(int argc, char *argv[])
>  	if (!read_efi_section(buf)) {
>  	    buf += 32;
>  	    if (!read_efi_catalogue(buf, &mac_count, &mac_lba) && mac_lba) {
> -		offset = 1;
> -		type = 0xee;
> +		offset = 0;
>  	    } else {
>  		errx(1, "%s: invalid efi catalogue", argv[0]);
>  	    }
> -- 
> 1.7.7.6
> 
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-- 
Groeten
Geert Stappers
-- 
> And is there a policy on top-posting vs. bottom-posting?
Yes.