linux-kernel - [PATCH 4.4 24/56] x86/build: Add -Wnoaddress-of-packed-member to REALMODE

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Date:   Fri, 20 Sep 2019 00:04:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 4.4 24/56] x86/build: Add -Wnoaddress-of-packed-member to REALMODE_CFLAGS, to silence GCC9 build warning

From: Linus Torvalds <torvalds@...ux-foundation.org>

commit 42e0e95474fc6076b5cd68cab8fa0340a1797a72 upstream.

One of the very few warnings I have in the current build comes from
arch/x86/boot/edd.c, where I get the following with a gcc9 build:

   arch/x86/boot/edd.c: In function ‘query_edd’:
   arch/x86/boot/edd.c:148:11: warning: taking address of packed member of ‘struct boot_params’ may result in an unaligned pointer value [-Waddress-of-packed-member]
     148 |  mbrptr = boot_params.edd_mbr_sig_buffer;
         |           ^~~~~~~~~~~

This warning triggers because we throw away all the CFLAGS and then make
a new set for REALMODE_CFLAGS, so the -Wno-address-of-packed-member we
added in the following commit is not present:

  6f303d60534c ("gcc-9: silence 'address-of-packed-member' warning")

The simplest solution for now is to adjust the warning for this version
of CFLAGS as well, but it would definitely make sense to examine whether
REALMODE_CFLAGS could be derived from CFLAGS, so that it picks up changes
in the compiler flags environment automatically.

Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Acked-by: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/Makefile |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -38,6 +38,7 @@ REALMODE_CFLAGS	:= $(M16_CFLAGS) -g -Os
 
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
+REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
 REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
 export REALMODE_CFLAGS