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   1 From 42e0e95474fc6076b5cd68cab8fa0340a1797a72 Mon Sep 17 00:00:00 2001
   2 From: Linus Torvalds <torvalds@linux-foundation.org>
   3 Date: Wed, 28 Aug 2019 10:56:48 +0200
   4 Subject: x86/build: Add -Wnoaddress-of-packed-member to REALMODE_CFLAGS, to silence GCC9 build warning
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   8
   9 From: Linus Torvalds <torvalds@linux-foundation.org>
  10
  11 commit 42e0e95474fc6076b5cd68cab8fa0340a1797a72 upstream.
  12
  13 One of the very few warnings I have in the current build comes from
  14 arch/x86/boot/edd.c, where I get the following with a gcc9 build:
  15
  16    arch/x86/boot/edd.c: In function ‘query_edd’:
  17    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]
  18      148 |  mbrptr = boot_params.edd_mbr_sig_buffer;
  19          |           ^~~~~~~~~~~
  20
  21 This warning triggers because we throw away all the CFLAGS and then make
  22 a new set for REALMODE_CFLAGS, so the -Wno-address-of-packed-member we
  23 added in the following commit is not present:
  24
  25   6f303d60534c ("gcc-9: silence 'address-of-packed-member' warning")
  26
  27 The simplest solution for now is to adjust the warning for this version
  28 of CFLAGS as well, but it would definitely make sense to examine whether
  29 REALMODE_CFLAGS could be derived from CFLAGS, so that it picks up changes
  30 in the compiler flags environment automatically.
  31
  32 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  33 Acked-by: Borislav Petkov <bp@alien8.de>
  34 Cc: Peter Zijlstra <peterz@infradead.org>
  35 Cc: Thomas Gleixner <tglx@linutronix.de>
  36 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38
  39 ---
  40  arch/x86/Makefile |    1 +
  41  1 file changed, 1 insertion(+)
  42
  43 --- a/arch/x86/Makefile
  44 +++ b/arch/x86/Makefile
  45 @@ -38,6 +38,7 @@ REALMODE_CFLAGS       := $(M16_CFLAGS) -g -Os
  46
  47  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -ffreestanding)
  48  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -fno-stack-protector)
  49 +REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), -Wno-address-of-packed-member)
  50  REALMODE_CFLAGS += $(call __cc-option, $(CC), $(REALMODE_CFLAGS), $(cc_stack_align4))
  51  export REALMODE_CFLAGS
  52