• Gustavo A. R. Silva's avatar
    KVM: VMX: Replace zero-length array with flexible-array · f4a9fdd5
    Gustavo A. R. Silva authored
    The current codebase makes use of the zero-length array language
    extension to the C90 standard, but the preferred mechanism to declare
    variable-length types such as these ones is a flexible array member[1][2],
    introduced in C99:
    
    struct foo {
            int stuff;
            struct boo array[];
    };
    
    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
    inadvertently introduced[3] to the codebase from now on.
    
    Also, notice that, dynamic memory allocations won't be affected by
    this change:
    
    "Flexible array members have incomplete type, and so the sizeof operator
    may not be applied. As a quirk of the original implementation of
    zero-length arrays, sizeof evaluates to zero."[1]
    
    sizeof(flexible-array-member) triggers a warning because flexible array
    members have incomplete type[1]. There are some instances of code in
    which the sizeof operator is being incorrectly/erroneously applied to
    zero-length arrays and the result is zero. Such instances may be hiding
    some bugs. So, this work (flexible-array member conversions) will also
    help to get completely rid of those sorts of issues.
    
    This issue was found with the help of Coccinelle.
    
    [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
    [2] https://github.com/KSPP/linux/issues/21
    [3] commit 76497732
    
     ("cxgb3/l2t: Fix undefined behaviour")
    Signed-off-by: default avatarGustavo A. R. Silva <gustavoars@kernel.org>
    Message-Id: <20200507185618.GA14831@embeddedor>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    f4a9fdd5
vmcs.h 3.57 KB