Re: [PATCH 0/8] fix gcc9 build with -Werror=address-of-packed-member

[Michael Chang]

On Tue, Apr 09, 2019 at 08:57:25PM +1000, Vladimir 'phcoder' Serbinenko wrote:
> On Tue, Apr 9, 2019 at 8:48 PM Michael Chang <address@hidden> wrote:
> >
> > This patch set attempts to resolve the build failure in openSUSE build
> > service equipped with new gcc 9 compiler, which has added a new warning
> > flag -Waddress-of-packed-member.
> >
> > The new warning performs the check for taking the address of packed
> > member directly to a pointer variable with higher alignment requirement
> > and the outcome is risky to memory alignment fault on some architecture
> > when deferencing it.
> The problem here is that there is no way to tell the compiler to
> create a structure without padding but a pointer to which is aligned.
> This is very common in GRUB. Consider a struct like following:
> grub_uint16_t a;
> grub_uint32_t b;
> grub_uint16_t c[40];
> 
> This needs packed attribute as otherwise compiler will insert a
> padding before b. Yet c is guaranteed to be aligned if the pointer to
> the structure is aligned.

But sometimes it is not easy to know as the packed structure could be
embedded to another and also it could map to a specific portion in
memory read from a file, with no guarantee where will be started (for eg
via searching occurrence of specific magic number ..)

Thanks,
Michael

> >
> > Please help to review.
> >
> > Thanks.
> >
> > Michael Chang (8):
> >   cpio: fix gcc9 error address-of-packed-member
> >   jfs: fix gcc9 error address-of-packed-member
> >   hfs: fix gcc9 error address-of-packed-member
> >   hfsplus: fix gcc9 error address-of-packed-member
> >   acpi: fix gcc9 error address-of-packed-member
> >   usbtest: fix gcc9 error address-of-packed-member
> >   chainloader: fix gcc9 error address-of-packed-member
> >   efi: fix gcc9 error address-of-packed-member
> >
> >  grub-core/commands/usbtest.c       | 13 ++++++++-
> >  grub-core/fs/cpio.c                |  5 ++--
> >  grub-core/fs/cpio_be.c             |  5 ++--
> >  grub-core/fs/hfsplus.c             | 57 
> > ++++++++++++++++++++++++++------------
> >  grub-core/fs/jfs.c                 |  5 ++--
> >  grub-core/kern/efi/efi.c           | 27 ++++++++++++++++--
> >  grub-core/loader/efi/chainloader.c | 12 ++++++--
> >  include/grub/acpi.h                |  2 +-
> >  include/grub/hfs.h                 |  2 +-
> >  9 files changed, 96 insertions(+), 32 deletions(-)
> >
> > --
> > 2.16.4
> >
> >
> > _______________________________________________
> > Grub-devel mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/grub-devel
> 
> 
> 
> -- 
> Regards
> Vladimir 'phcoder' Serbinenko
> 
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