Ok, that's what I finally convinced myself, too. Thanks for the confirmation.
- Andy On Wed, Mar 4, 2015 at 4:24 PM, Scott Perry <numist at apple.com> wrote: > Good eye, thanks for reporting this. > > Pointers on the stack or in static storage are pointer-aligned by default on > all of Apple's platforms. > > On Mar 3, 2015, at 7:27 PM, Andy Rahn <andy.rahn at gmail.com> wrote: >> >> Hi SQLite users; >> >> I have a question about _sqliteZone_ in mem1.c. I notice that the >> address of this static variable is used in a call to >> OSAtomicCompareAndSwapPtrBarrier on MacOS and iOS. That system call >> is declared in OSAtomic.h, which includes a note about the pointer >> alignment of its arguments: >> >>> * WARNING: all addresses passed to these functions must be "naturally >>> aligned", >>> * i.e. * <code>int32_t</code> pointers must be 32-bit aligned (low 2 bits >>> of >>> * address are zeroes), and <code>int64_t</code> pointers must be 64-bit >>> aligned >>> * (low 3 bits of address are zeroes.) >> >> I wonder, therefore, if it might be prudent to declare _sqliteZone_ >> with the alignment attribute, so that the compiler is sure to put it >> at a 32 / 64 bit aligned address space? e .g. >> >> static __attribute__((aligned(8))) malloc_zone_t* _sqliteZone_; >> >> and also, because this local variable is used in that same function: >> >> __attribute__((aligned(8))) malloc_zone_t* newzone = >> malloc_create_zone(4096, 0); >> >> I see that attribute is used one other place, so this may be an >> important nuance. On a 32-bit architecture, it would be safe to use >> aligned(4) instead of aligned(8) but I'm not sure anyone will care >> about the (possible) 4-byte savings. >> >> - Andy >> _______________________________________________ >> sqlite-users mailing list >> sqlite-users at mailinglists.sqlite.org >> http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
