From de88a9628426e82f1cee4b61b06e67e6787301b1 Mon Sep 17 00:00:00 2001 From: Paul Menzel Date: Wed, 4 Mar 2020 14:51:27 +0100 Subject: std/tcg: Replace zero-length array with flexible-array member MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 '() + 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); | ~~~~~~~~~~~~~~~~~~~~~^~~~~~~ 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 '() + 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 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 Reviewed-by: Philippe Mathieu-Daudé --- 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 1cc1c925..1c9eeb4e 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]; -- cgit