cgpt: add support for managing the legacy boot gpt bitstabilize-kevin-8785.94.B

Bit 2 in the GPT partition attributes has been allocated as the legacy
bios boot (equivalent to the "active" or "boot" flag in MBR).  If we
try to boot images on newer x86 systems, syslinux dies because it can't
find any GPT partition marked bootable.

Update the various parts of cgpt add & show to manage this bit.  Now we
can run:
	cgpt add -i 12 -B 1 chromiumos_image.bin
And the EFI partition will be marked bootable.

BUG=chromium:644845
TEST=vboot_reference unittests pass
TEST=booted an amd64-generic disk image via USB on a generic laptop
BRANCH=None

Change-Id: I78e17b8df5b0c61e9e2d8a3c703e6d5ad230fe92
Reviewed-on: https://chromium-review.googlesource.com/382411
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/cgpt/cgpt_common.c b/cgpt/cgpt_common.c
index 29906d40..1a6bd3cb 100644
--- a/cgpt/cgpt_common.c
+++ b/cgpt/cgpt_common.c
@@ -763,6 +763,20 @@ GptEntry *GetEntry(GptData *gpt, int secondary, uint32_t entry_index) {
   return (GptEntry*)(&entries[stride * entry_index]);
 }
 
+void SetLegacyBoot(struct drive *drive, int secondary, uint32_t entry_index,
+                   int legacy_boot) {
+  require(legacy_boot >= 0 && legacy_boot <= CGPT_ATTRIBUTE_MAX_LEGACY_BOOT);
+  GptEntry *entry;
+  entry = GetEntry(&drive->gpt, secondary, entry_index);
+  SetEntryLegacyBoot(entry, legacy_boot);
+}
+
+int GetLegacyBoot(struct drive *drive, int secondary, uint32_t entry_index) {
+  GptEntry *entry;
+  entry = GetEntry(&drive->gpt, secondary, entry_index);
+  return GetEntryLegacyBoot(entry);
+}
+
 void SetPriority(struct drive *drive, int secondary, uint32_t entry_index,
                  int priority) {
   require(priority >= 0 && priority <= CGPT_ATTRIBUTE_MAX_PRIORITY);