Global constants

[Mark McLoughlin]

Hi,
	Trying out systemtap, I found myself doing the likes of:

    ---
    global O_CREAT

    probe begin {
        O_CREAT = 64
    }

    probe kernel.function ("sys_open") {
        if ($flags & O_CREAT) {
            printf ("foo\n");
        }
    }
    ---

	Then I thought it might be handy to have these kind of globals defined
in the system tapsets so I patched stap with:

    ---
       o->newline() << "static rwlock_t "
                    << "global_" << c_varname (v->name) << "_lock;";
    +  o->newline() << "#define global_"
    +               << c_varname(v->name) << "_DEFINED 1";
    ---

	and put the likes of this in the system tapsets:

    ---
    global O_CREAT

    function init_sys_open_flags () %{
    #ifdef global_O_CREAT_DEFINED
        global_O_CREAT = 64;
    #endif
    %}

    probe begin {
        init_sys_open_flags ();
    }
    ---

	But then I thought that perhaps support for global constants like this
in the language wouldn't be such a bad idea, so you could just do:

    ---
    const O_CREAT = 64

    probe kernel.function ("sys_open") {
        if ($flags & O_CREAT) {
            printf ("foo\n");
        }
    }
    ---

	Attached is a patch which implements this. The patch still needs closer
review, a bit of tidying up, perhaps some more optimisations for
constants, test cases for it in the test suite etc. but it does
basically seem to work. I thought I'd send it here for comments before
finishing it off.

	So, thoughts?

Thanks,
Mark
-------------- next part --------------
A non-text attachment was scrubbed...
Name: systemtap-0.5.4-global-constants.patch
Type: text/x-patch
Size: 45568 bytes
Desc: not available
URL: <http://sourceware.org/pipermail/systemtap/attachments/20060213/c6346a1f/attachment.bin>