36126f8f2e
This changes the interfaces in <asm/word-at-a-time.h> to be a bit more complicated, but a lot more generic. In particular, it allows us to really do the operations efficiently on both little-endian and big-endian machines, pretty much regardless of machine details. For example, if you can rely on a fast population count instruction on your architecture, this will allow you to make your optimized <asm/word-at-a-time.h> file with that. NOTE! The "generic" version in include/asm-generic/word-at-a-time.h is not truly generic, it actually only works on big-endian. Why? Because on little-endian the generic algorithms are wasteful, since you can inevitably do better. The x86 implementation is an example of that. (The only truly non-generic part of the asm-generic implementation is the "find_zero()" function, and you could make a little-endian version of it. And if the Kbuild infrastructure allowed us to pick a particular header file, that would be lovely) The <asm/word-at-a-time.h> functions are as follows: - WORD_AT_A_TIME_CONSTANTS: specific constants that the algorithm uses. - has_zero(): take a word, and determine if it has a zero byte in it. It gets the word, the pointer to the constant pool, and a pointer to an intermediate "data" field it can set. This is the "quick-and-dirty" zero tester: it's what is run inside the hot loops. - "prep_zero_mask()": take the word, the data that has_zero() produced, and the constant pool, and generate an *exact* mask of which byte had the first zero. This is run directly *outside* the loop, and allows the "has_zero()" function to answer the "is there a zero byte" question without necessarily getting exactly *which* byte is the first one to contain a zero. If you do multiple byte lookups concurrently (eg "hash_name()", which looks for both NUL and '/' bytes), after you've done the prep_zero_mask() phase, the result of those can be or'ed together to get the "either or" case. - The result from "prep_zero_mask()" can then be fed into "find_zero()" (to find the byte offset of the first byte that was zero) or into "zero_bytemask()" (to find the bytemask of the bytes preceding the zero byte). The existence of zero_bytemask() is optional, and is not necessary for the normal string routines. But dentry name hashing needs it, so if you enable DENTRY_WORD_AT_A_TIME you need to expose it. This changes the generic strncpy_from_user() function and the dentry hashing functions to use these modified word-at-a-time interfaces. This gets us back to the optimized state of the x86 strncpy that we lost in the previous commit when moving over to the generic version. Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
69 lines
1.5 KiB
Makefile
69 lines
1.5 KiB
Makefile
include include/asm-generic/Kbuild.asm
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header-y += elf.h
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header-y += ucontext.h
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generic-y += atomic.h
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generic-y += auxvec.h
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generic-y += barrier.h
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generic-y += bitsperlong.h
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generic-y += bug.h
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generic-y += bugs.h
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generic-y += cacheflush.h
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generic-y += checksum.h
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generic-y += cmpxchg.h
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generic-y += cmpxchg-local.h
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generic-y += cpumask.h
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generic-y += cputime.h
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generic-y += current.h
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generic-y += device.h
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generic-y += div64.h
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generic-y += dma.h
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generic-y += emergency-restart.h
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generic-y += errno.h
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generic-y += exec.h
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generic-y += fb.h
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generic-y += fcntl.h
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generic-y += ftrace.h
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generic-y += futex.h
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generic-y += hardirq.h
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generic-y += hw_irq.h
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generic-y += ioctl.h
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generic-y += ioctls.h
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generic-y += ipcbuf.h
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generic-y += irq_regs.h
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generic-y += kdebug.h
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generic-y += kmap_types.h
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generic-y += local.h
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generic-y += mman.h
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generic-y += module.h
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generic-y += msgbuf.h
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generic-y += pci.h
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generic-y += percpu.h
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generic-y += poll.h
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generic-y += posix_types.h
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generic-y += resource.h
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generic-y += rmap.h
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generic-y += scatterlist.h
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generic-y += sections.h
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generic-y += segment.h
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generic-y += sembuf.h
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generic-y += setup.h
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generic-y += shmbuf.h
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generic-y += shmparam.h
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generic-y += siginfo.h
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generic-y += signal.h
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generic-y += socket.h
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generic-y += sockios.h
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generic-y += statfs.h
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generic-y += stat.h
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generic-y += string.h
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generic-y += switch_to.h
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generic-y += swab.h
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generic-y += termbits.h
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generic-y += termios.h
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generic-y += topology.h
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generic-y += types.h
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generic-y += ucontext.h
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generic-y += user.h
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generic-y += word-at-a-time.h
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