Re: [PATCH] gcc/doc: list what version each attribute was introduced in

[Jeff Law <law@redhat.com>]

On 07/06/2017 07:25 AM, Daniel P. Berrange wrote:
> There are several hundred named attribute keys that have been
> introduced over many GCC releases. Applications typically need
> to be compilable with multiple GCC versions, so it is important
> for developers to know when GCC introduced support for each
> attribute.
> 
> This augments the texi docs that list attribute keys with
> a note of what version introduced the feature. The version
> information was obtained through archaeology of the GCC source
> repository release tags, back to gcc-4_0_0-release. For
> attributes added in 4.0.0 or later, an explicit version will
> be noted. Any attribute that predates 4.0.0 will simply note
> that it has existed prior to 4.0.0. It is thought there is
> little need to go further back in time than 4.0.0 since few,
> if any, apps will still be using such old compiler versions.
> 
> Where a named attribute can be used in many contexts (ie the
> 'visibility' attribute can be used for both functions or
> variables), it was assumed that the attribute was supported
> in all use contexts at the same time.
> 
> Future patches that add new attributes to GCC should be
> required to follow this new practice, by documenting the
> version.
Keying on version #s is generally a terrible way to make your code
portable.  It's easy to get wrong and due to backporting there's not
always a strong tie between a version number and the existence of a
particular feature.

It's far better to actually *test* what your particular compiler
compiler supports.  I suspect autoconf, for example, probably has some
infrastructure for testing if specific attributes are supported by the
compiler.

Jeff