On Wed, Mar 04, 2020 at 02:51:27PM +0100, Paul Menzel wrote:
> Date: Tue, 3 Mar 2020 16:24:46 +0100
>
> GCC 10 gives the warnings below:
>
> In file included from out/ccode32flat.o.tmp.c:54:
> ./src/tcgbios.c: In function 'tpm20_write_EfiSpecIdEventStruct':
> ./src/tcgbios.c:290:30: warning: array subscript '(<unknown>) +
> 4294967295' is outside the bounds of an interior zero-length array 'struct
> TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> 290 | event.hdr.digestSizes[count].algorithmId =
> be16_to_cpu(sel->hashAlg);
> | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
Thanks. It looks fine to me. Stefan - do you have any comments on this?
-Kevin
> In file included from ./src/tcgbios.c:22,
> from out/ccode32flat.o.tmp.c:54:
> ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> 527 | } digestSizes[0];
> | ^~~~~~~~~~~
> In file included from out/ccode32flat.o.tmp.c:54:
> ./src/tcgbios.c:291:30: warning: array subscript '(<unknown>) +
> 4294967295' is outside the bounds of an interior zero-length array 'struct
> TCG_EfiSpecIdEventAlgorithmSize[0]' [-Wzero-length-bounds]
> 291 | event.hdr.digestSizes[count].digestSize = hsize;
> | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
> In file included from ./src/tcgbios.c:22,
> from out/ccode32flat.o.tmp.c:54:
> ./src/std/tcg.h:527:7: note: while referencing 'digestSizes'
> 527 | } digestSizes[0];
> | ^~~~~~~~~~~
>
> [Description copied from Gustavo A. R. Silva <gust...@embeddedor.com>
> from his Linux kernel commits.]
>
> 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]
>
> 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=76497732932f15e7323dc805e8ea8dc11bb587cf
>
> Signed-off-by: Paul Menzel <pmen...@molgen.mpg.de>
> Reviewed-by: Philippe Mathieu-Daudé <phi...@redhat.com>
> ---
> v2: Cite all references, add Reviewed-by line
>
> src/std/tcg.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/std/tcg.h b/src/std/tcg.h
> index 1cc1c92..1c9eeb4 100644
> --- a/src/std/tcg.h
> +++ b/src/std/tcg.h
> @@ -524,7 +524,7 @@ struct TCG_EfiSpecIdEventStruct {
> struct TCG_EfiSpecIdEventAlgorithmSize {
> u16 algorithmId;
> u16 digestSize;
> - } digestSizes[0];
> + } digestSizes[];
> /*
> u8 vendorInfoSize;
> u8 vendorInfo[0];
> --
> 2.25.0
>
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