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

syslinux-bot for Matthew Garrett mjg at redhat.com
Mon Mar 26 14:51:07 PDT 2012


Commit-ID:  ead636d9693089bc54f1272552ae50b70d3f3965
Gitweb:     http://www.syslinux.org/commit/ead636d9693089bc54f1272552ae50b70d3f3965
Author:     Matthew Garrett <mjg at redhat.com>
AuthorDate: Wed, 15 Feb 2012 12:12:17 -0500
Committer:  H. Peter Anvin <hpa at linux.intel.com>
CommitDate: Mon, 26 Mar 2012 14:49:09 -0700

isohybrid: Generate MBR even when in EFI mode

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.

Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>

---
 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]);
 	    }


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