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| /freebsd-10.1-release/sys/cddl/contrib/opensolaris/common/nvpair/ | ||
| H A D | nvpair.c | diff 196269 Sat Aug 15 23:53:12 MDT 2009 marcel Fix misalignment in nvpair_native_embedded() caused by the compiler replacing the bzero(). See also revision 195627, which fixed the misalignment in nvpair_native_embedded_array(). Approved by: re (kensmith) diff 195627 Sat Jul 11 20:45:15 MDT 2009 marcel In nvpair_native_embedded_array(), meaningless pointers are zeroed. The programmer was aware that alignment was not guaranteed in the packed structure and used bzero() to NULL out the pointers. However, on ia64, the compiler is quite agressive in finding ILP and calls to bzero() are often replaced by simple assignments (i.e. stores). Especially when the width or size in question corresponds with a store instruction (i.e. st1, st2, st4 or st8). The problem here is not a compiler bug. The address of the memory to zero-out was given by '&packed->nvl_priv' and given the type of the 'packed' pointer the compiler could assume proper alignment for the replacement of bzero() with an 8-byte wide store to be valid. The problem is with the programmer. The programmer knew that the address did not have the alignment guarantees needed for a regular assignment, but failed to inform the compiler of that fact. In fact, the programmer told the compiler the opposite: alignment is guaranteed. The fix is to avoid using a pointer of type "nvlist_t *" and instead use a "char *" pointer as the basis for calculating the address. This tells the compiler that only 1-byte alignment can be assumed and the compiler will either keep the bzero() call or instead replace it with a sequence of byte-wise stores. Both are valid. Approved by: re (kib) |
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