On Thu, Feb 02, 2023 at 07:24:50PM -0600, Gustavo A. R. Silva wrote: > One-element arrays are deprecated, and we are replacing them with flexible > array members instead. So, replace one-element arrays with flexible-array > members in structures xfs_attr_leaf_name_local and > xfs_attr_leaf_name_remote. > > The only binary differences reported after the changes are all like > these: > > fs/xfs/libxfs/xfs_attr_leaf.o > _@@ -435,7 +435,7 @@ > 3b8: movzbl 0x2(%rbx),%eax > 3bc: rol $0x8,%bp > 3c0: movzwl %bp,%ebp > - 3c3: lea 0x2(%rax,%rbp,1),%ebx > + 3c3: lea 0x3(%rax,%rbp,1),%ebx > 3c7: call 3cc <xfs_attr_leaf_entsize+0x8c> > 3c8: R_X86_64_PLT32 __tsan_func_exit-0x4 > 3cc: or $0x3,%ebx > _@@ -454,7 +454,7 @@ > 3ea: movzbl 0x8(%rbx),%ebx > 3ee: call 3f3 <xfs_attr_leaf_entsize+0xb3> > 3ef: R_X86_64_PLT32 __tsan_func_exit-0x4 > - 3f3: add $0xa,%ebx > + 3f3: add $0xb,%ebx > 3f6: or $0x3,%ebx > 3f9: add $0x1,%ebx > 3fc: mov %ebx,%eax > > similar changes in fs/xfs/scrub/attr.o and fs/xfs/xfs.o object files. I usually turn off the sanitizers for the A/B build comparisons to make it easier to read the results. It looks like it _grew_ in size here, though? > And the reason for this is because of the round_up() macro called in > functions xfs_attr_leaf_entsize_remote() and xfs_attr_leaf_entsize_local(), > which is compensanting for the one-byte reduction in size (due to the > flex-array transformation) of structures xfs_attr_leaf_name_remote and > xfs_attr_leaf_name_local. So, sizes remain the same before and after > changes. > > This helps with the ongoing efforts to tighten the FORTIFY_SOURCE > routines on memcpy() and help us make progress towards globally > enabling -fstrict-flex-arrays=3 [1]. > > Link: https://github.com/KSPP/linux/issues/79 > Link: https://github.com/KSPP/linux/issues/251 > Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1] > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> If xfstests pass, this seems good to me. Thanks! Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
