From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 25 May 2012 15:35:38 -0700 (PDT)
> So it's not truly generic, but it's in lib/strnlen_user.c and under the
> CONFIG_GENERIC_STRNLEN_USER config option, because I'm convinced it should
> be possible to do something that does the right thing for everybody.
It should be relatively easy, especially since you work with aligned
words.
> What's the appropriate *clean* interface to allow architectures
> to tweak the little details?
Maybe something like:
#define HAS_ZERO_CONST_DECLARE ...
#define HAS_ZERO_VAR_DECLARE ...
#define HAS_ZERO_ARGS ...
static inline unsigned long has_zero(unsigned long c ...)
{
}
#define FIND_ZERO_ARGS ...
static inline long find_zero(unsigned long c, unsigned long mask ...)
{
}
So at the use sites it's something like:
long do_strwhatever_user()
{
HAS_ZERO_CONST_DECLARE;
...
while (max >= sizeof(unsigned long)) {
unsigned long mask, c;
HAS_ZERO_VAR_DECLARE;
mask = has_zero(c HAS_ZERO_ARGS);
if (mask)
return res + find_zero(c, mask FIND_ZERO_ARGS);
...
}
...
}
A little ugly. The main problem is the magic args macros.
We can kill off the HAS_ZERO_CONST_DECLARE booger by instead
exposing the magic constants used by the particular has_zero()
implementation. Then we'll have:
#define HAVE_ZERO_CONST1 REPEAT_BYTE(X)
#define HAVE_ZERO_CONST2 REPEAT_BYTE(X)
static inline unsigned long has_zero(unsigned long c,
const unsigned long magic1,
const unsigned long magic2);
and then it becomes something like:
long do_strwhatever_user()
{
const unsigned long magic1 = HAVE_ZERO_CONST1;
const unsigned long magic2 = HAVE_ZERO_CONST2;
...
while (max >= sizeof(unsigned long)) {
unsigned long mask, c;
HAS_ZERO_VAR_DECLARE;
mask = has_zero(c, magic1, magic2);
if (mask)
return res + find_zero(c, mask, magic1, magic2);
The remaining problem, which I was trying to accomodate with the funky
ARGS macros, is propagating part of the has_zero() calculation into the
find_zero() call.
Hmmm...
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