From b98ba8921010d03f46704a476c69861515deb1ca Mon Sep 17 00:00:00 2001
From: Peter Jones <pjones@redhat.com>
Date: Mon, 7 Jan 2019 10:30:59 -0500
Subject: [PATCH] dp.h: make format_guid() handle misaligned guid pointers
 safely.

GCC 9 adds -Werror=address-of-packed-member, which causes us to see the
build error reported at
 https://bugzilla.opensuse.org/show_bug.cgi?id=1120862 .

That bug report shows us the following:

In file included from dp.c:26:
dp.h: In function 'format_vendor_helper':
dp.h:120:37: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value [-Werror=address-of-packed-member]
  120 |  format_guid(buf, size, off, label, &dp->hw_vendor.vendor_guid);
      |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~
dp.h:74:25: note: in definition of macro 'format_guid'
   74 |   _rc = efi_guid_to_str(guid, &_guidstr);   \
      |                         ^~~~
cc1: all warnings being treated as errors

This patch makes format_guid() use a local variable as a bounce buffer
in the case that the guid we're passed is aligned as chaotic neutral.

Note that this only fixes this instance and there may be others that bz
didn't show because it exited too soon, and I don't have a gcc 9 build
in front of me right now.

Signed-off-by: Peter Jones <pjones@redhat.com>
---
 src/dp.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/dp.h b/src/dp.h
index aa4e390..20cb608 100644
--- a/src/dp.h
+++ b/src/dp.h
@@ -70,8 +70,15 @@
 #define format_guid(buf, size, off, dp_type, guid) ({			\
 		int _rc;						\
 		char *_guidstr = NULL;					\
-									\
-		_rc = efi_guid_to_str(guid, &_guidstr);			\
+		efi_guid_t _guid;					\
+		const efi_guid_t * const _guid_p =			\
+			likely(__alignof__(guid) == sizeof(guid))	\
+				? guid					\
+				: &_guid;				\
+								        \
+		if (unlikely(__alignof__(guid) == sizeof(guid)))	\
+			memmove(&_guid, guid, sizeof(_guid));		\
+		_rc = efi_guid_to_str(_guid_p, &_guidstr);		\
 		if (_rc < 0) {						\
 			efi_error("could not build %s GUID DP string",	\
 				  dp_type);				\