[PATCH 2/6] Add returns_zero_on_success/failure attributes

Joseph Myers joseph@codesourcery.com
Wed Nov 17 22:43:58 GMT 2021


On Wed, 17 Nov 2021, Prathamesh Kulkarni via Gcc-patches wrote:

> More generally, would it be a good idea to provide attributes for
> mod/ref anaylsis ?
> So sth like:
> void foo(void) __attribute__((modifies(errno)));
> which would state that foo modifies errno, but neither reads nor
> modifies any other global var.
> and
> void bar(void) __attribute__((reads(errno)))
> which would state that bar only reads errno, and doesn't modify or
> read any other global var.

Many math.h functions are const except for possibly setting errno, 
possibly raising floating-point exceptions (which might have other effects 
when using alternate exception handling) and possibly reading the rounding 
mode.  To represent that, it might be useful for such attributes to be 
able to describe state (such as the floating-point environment) that 
doesn't correspond to a C identifier.  (errno tends to be a macro, so 
referring to it as such in an attribute may be awkward as well.)

(See also <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2825.htm> with 
some proposals for features to describe const/pure-like properties of 
functions.)

-- 
Joseph S. Myers
joseph@codesourcery.com


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