https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94300
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:f1154b4d3c54e83d493cc66d1a30c410b9b3108a commit r10-7366-gf1154b4d3c54e83d493cc66d1a30c410b9b3108a Author: Jakub Jelinek <ja...@redhat.com> Date: Wed Mar 25 09:17:01 2020 +0100 sccvn: Fix buffer overflow in push_partial_def [PR94300] The following testcase is miscompiled, because there is a buffer overflow in push_partial_def in the little-endian case when working 64-byte vectors. The code computes the number of bytes we need in the BUFFER: NEEDED_LEN, which is rounded up number of bits we need. Then the code native_encode_expr each (partially overlapping) pd into THIS_BUFFER. If pd.offset < 0, i.e. the pd.rhs store starts at some bits before the window we are interested in, we pass -pd.offset to native_encode_expr and shrink the size already earlier: HOST_WIDE_INT size = pd.size; if (pd.offset < 0) size -= ROUND_DOWN (-pd.offset, BITS_PER_UNIT); On this testcase, the problem is with a store with pd.offset > 0, in particular pd.offset 256, pd.size 512, i.e. a 64-byte store which doesn't fit into entirely into BUFFER. We have just: size = MIN (size, (HOST_WIDE_INT) needed_len * BITS_PER_UNIT); in this case for little-endian, which isn't sufficient, because needed_len is 64, the entire BUFFER (except of the last extra byte used for shifting). native_encode_expr fills the whole THIS_BUFFER (again, except the last extra byte), and the code then performs memcpy (BUFFER + 32, THIS_BUFFER, 64); which overflows BUFFER and as THIS_BUFFER is usually laid out after it, overflows it into THIS_BUFFER. The following patch fixes it by for pd.offset > 0 making sure size is reduced too. For big-endian the code does things differently and already handles this right. 2020-03-25 Jakub Jelinek <ja...@redhat.com> PR tree-optimization/94300 * tree-ssa-sccvn.c (vn_walk_cb_data::push_partial_def): If pd.offset is positive, make sure that off + size isn't larger than needed_len. * gcc.target/i386/avx512f-pr94300.c: New test.
