On Tue, 2015-12-29 at 11:37 -0800, John Baldwin wrote: > On Monday, December 28, 2015 01:01:26 PM Warner Losh wrote: > > I'll look at that, but I don't think posix_memalign is the right > > way to go. > > The alignment of FILE is more strict than posix_memalign will > > return. Ian's > > idea of __alignof__ is the way to go. We allocate them in one block > > on > > purpose for performance, and posix_memalign would be a one at a > > time affair. > > posix_memalign gives you whatever alignment you ask for. Using > __alignof__ > to determine the alignment instead of hardcoding sizeof(int64_t) > would > certainly be an improvement. If you move the glue after the FILE > objects > then you can use posix_memalign() directly as so: > > void *mem; > int error; > > error = posix_memalign(&mem, MAX(ALIGNBYTES, > __alignof__(mbstate_t)), > n * sizeof(FILE) + sizeof(*g)); > if (error) > return (NULL); > p = (FILE *)mem; > g = (struct glue *)(p + n); > g->next = NULL; > g->niobs = n; > g->iobs = p; > ... > > (This presumes that the requested alignment of 'struct glue' is less > than > the alignment needed by FILE which should be true.) >
If there's going to be an assumption that __alignof__(glue) <= __alignof__(FILE), it might be nice to have a static_assert() of that to prevent a future time bomb similar to the one that exploded on arm when it turned out the opposite assumption was wrong. -- Ian _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
