Using do_alloca() instead of emalloc()

Hey,

I've been taking a look at the __autoload problem. During that time I saw
that lots of places in the code (especially reflection API) use
zend_str_tolower_dup().
[...]

Here's a patch for zend_reflection_api.c which uses do_alloca /
free_alloca in all relevant places.

• Timm

Hello Andi,

Thursday, November 20, 2003, 10:48:57 AM, you wrote:

Hey,

I've been taking a look at the __autoload problem. During that time I saw
that lots of places in the code (especially reflection API) use
zend_str_tolower_dup().
In most of these cases it would be much more efficient to use
do_alloca()/free_alloca() because that usually uses alloca() which
allocates on the stack.

Well Zeev and you told us to never it :-)

Simplified example from reflection API code:

lcname = zend_str_tolower_dup(name_str, name_len);

if (zend_hash_find(&ce->properties_info, lcname, name_len + 1, (void *)
&property_info) == FAILURE) {
efree(lcname);
/ Error message */
return;
}

efree(lcname);

This should really be:

lcname = do_alloca(name_len+1);
zend_str_tolower_copy(lcname, name_str, name_len+1);

if (zend_hash_find(&ce->properties_info, lcname, name_len + 1, (void *)
&property_info) == FAILURE) {
free_alloca(lcname);
/ Error message */
return;
}

free_alloca(lcname);

There are two times where you really shouldn't use do_alloca/free_alloca:
a) If you're in code which requires a regular malloc() don't use them (the
fallback is emalloc()).
b) Only use them in functions which are about to return. They shouldn't be
used in places like the main zend_execute loop because it would just make
the stack grow more and more (in almost all cases where
zend_str_tolower_dup() is being used, do_alloca/free_alloca are applicable).

I need to go away for the weekend now but it be cool if people here would
at least take care of this in their code (such as reflection API code).

Thanks,

Andi

--
Best regards,
Marcus mailto:helly@php.net

Commited thanks.
Marcus, what we meant was that you shouldn't use do_alloca() in the engine
except for in the cases I mentioned, and possibly cases where the
allocations would be quite large. In the case of reflection API the
allocations are small and the function returns right away, thus not
keeping stuff on the stack for too long.

Andi

At 11:09 PM 11/20/2003 +0100, Timm Friebe wrote:

Hey,

I've been taking a look at the __autoload problem. During that time I saw
that lots of places in the code (especially reflection API) use
zend_str_tolower_dup().
[...]

Here's a patch for zend_reflection_api.c which uses do_alloca /
free_alloca in all relevant places.

• Timm