[PATCH] avoid unaligned access when accessing poll stack (30c14e40) · Commits · 戴 / test

Commit : [PATCH] Optimize select/poll by putting small data sets on the stack resulted in the poll stack being 4-byte aligned on 64-bit architectures, causing misaligned accesses to elements in the array. This patch fixes it by declaring the stack in terms of 'long' instead of 'char'. Force alignment of poll and select stacks to long to avoid unaligned access on 64 bit architectures. Signed-off-by:

Jes Sorensen <jes@sgi.com> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

fs/select.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -314,7 +314,7 @@ static int core_sys_select(int n, fd_set __user inp, fd_set __user outp,
		int ret, size, max_fdset;
		struct fdtable *fdt;
		/* Allocate small arguments on the stack to save memory and be faster */
		char stack_fds[SELECT_STACK_ALLOC];
		long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];

		ret = -EINVAL;
		if (n < 0)
		@@ -639,8 +639,10 @@ int do_sys_poll(struct pollfd __user ufds, unsigned int nfds, s64 timeout)
		struct poll_list *walk;
		struct fdtable *fdt;
		int max_fdset;
		/* Allocate small arguments on the stack to save memory and be faster */
		char stack_pps[POLL_STACK_ALLOC];
		/* Allocate small arguments on the stack to save memory and be
		faster - use long to make sure the buffer is aligned properly
		on 64 bit archs to avoid unaligned access */
		long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
		struct poll_list *stack_pp = NULL;

		/* Do a sanity check on nfds ... */

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