On 11/29/2010 12:47 PM, Michael S. Tsirkin wrote:
On Mon, Nov 29, 2010 at 11:22:44AM +0200, Avi Kivity wrote:
> >> No need for an additional toolchain.
> >
> >It's a feature :) This way you are not forced to rewrite all code each
> >time you realize you need an extra check, and checks can be added
> >gradually without breaking build.
>
> You can see that user_ptr<> is not just for the checks, it adds
> functionality (sizeof-less copy_from and copy_to). That's usually
> the case. If there's something you must not do because of some
> rule, there's also something you want to do, and those become member
> functions.
>
> In C++ you could also introduce user_ptr<> gradually, it won't break
> anything.
Yes but in
void foo(void *p) {
bar(p);
}
both foo and bar must be converted.
No. You can convert from user_ptr<> to __user * and back.
> >Sparse has some advantages: it makes the contract obvious so you clearly
> >see it's a pointer and know ->, [], + will work, * and<< will not.
>
> I don't really see how you can tell this from __user.
I can tell this is a pointer from T *foo :), and I can tell
it has some attribute.
> You have to
> look up the definition. For user_ptr<>, the definition is actually
> available.
The definition for __user is also available:
#ifdef __CHECKER__
# define __user __attribute__((noderef, address_space(1)))
#else
# define __user
#endif
Which is a very transparent way to say: this is just a checker
attribute, it does not affect actual code.
Can you tell you must not dereference it?
With a template we go 'I have overridden + but compiler should
optimize it back to original'. Note the should :)
We do this in C all the time with pte_t and lots of inlines.
> Do a 'git grep hash' for examples of duplication.
I see. Don't know enough about tcg to fix unfortunately, but
the logic is different: e.g. sparc opcode table is completely
static, translation cache is dynamic, jump cache has
static size but dynamic content, qdict could do
with linear lookups just as well. So it could
just be different optimization strategies.
The default is duplication. With C++ your default is
tr1::unordered_map<> and you can optimize it later if you like.
--
error compiling committee.c: too many arguments to function
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