Re: Unit-at-a-time in real world (Re: Development plan *ducks*)

["Zack Weinberg" <zack at codesourcery dot com>]

Jan Hubicka <jh@suse.cz> writes:

>
> a) program referencing variables
>    from asm staements and not using __attribute__ ((used)).
>    Such problems we hit in glibc, prelink, wine and kernel.
>    One of anoying side effect is that the proper combination of flags for
>    such variable is __attribute__ ((used)) to instruct compiler to always
>    emit the variable *together* with __attribute__ ((unused)) that instruct
>    compiler to not emit warning.  This looks funny, so I would guess that
>    attribute used sould imply __attribute__ ((unused)) and set TREE_USED
>    flag too.  (do you follow the funny logic in the names)?

I think you're right, __attribute__ ((used)) should silence the
warning.  Send in a patch.

>    Another ugly thing is that 3.2 does not support attribute used on
>    variables so you need ifdef machinery.

Can the problem be avoided in another way, e.g. by putting the
variable into the operands list of the asm statement?

> b) using toplevel asm statements to change sections of functions (this
>    is present in gcc runtime and glibc).  The proper fix is to use gcc
>    section attributes or -fno-unit-at-a-time as work around.

The C++ front end, down the road, would be happier if -funit-at-a-time
were the *only* option.  So could you please do what it takes to make
sure there is another way to handle all such cases?  (Pathological
examples can be pushed off with 'rewrite in assembly'.)

zw