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    SubjectRe: [PATCH AUTOSEL 5.5 456/542] char: hpet: Use flexible-array member
    On Fri, Feb 14, 2020 at 10:47:28AM -0500, Sasha Levin wrote:
    > From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
    >
    > [ Upstream commit 987f028b8637cfa7658aa456ae73f8f21a7a7f6f ]
    >
    > Old code in the kernel uses 1-byte and 0-byte arrays to indicate the
    > presence of a "variable length array":
    >
    > struct something {
    > int length;
    > u8 data[1];
    > };
    >
    > struct something *instance;
    >
    > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
    > instance->length = size;
    > memcpy(instance->data, source, size);
    >
    > There is also 0-byte arrays. Both cases pose confusion for things like
    > sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism
    > to declare variable-length types such as the one above is a flexible array
    > member[2] which need to be the last member of a structure and empty-sized:
    >
    > struct something {
    > int stuff;
    > u8 data[];
    > };
    >
    > Also, by making use of the mechanism above, we will get a compiler warning
    > in case the flexible array does not occur last in the structure, which
    > will help us prevent some kind of undefined behavior bugs from being
    > unadvertenly introduced[3] to the codebase from now on.
    >
    > [1] https://github.com/KSPP/linux/issues/21
    > [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
    > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
    >
    > Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
    > Link: https://lore.kernel.org/r/20200120235326.GA29231@embeddedor.com
    > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > ---
    > drivers/char/hpet.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
    > index 9ac6671bb5141..aed2c45f7968c 100644
    > --- a/drivers/char/hpet.c
    > +++ b/drivers/char/hpet.c
    > @@ -110,7 +110,7 @@ struct hpets {
    > unsigned long hp_delta;
    > unsigned int hp_ntimer;
    > unsigned int hp_which;
    > - struct hpet_dev hp_dev[1];
    > + struct hpet_dev hp_dev[];
    > };
    >
    > static struct hpets *hpets;
    > --
    > 2.20.1
    >

    Not needed, please drop from all trees. Along with the other hpet patch
    that fixes the bug this one introduced :)

    thanks,

    greg k-h

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