Re: Using the asm suffix

[David Wohlferd <dw at LimeGreenSocks dot com>]

[snip]

> > how about replacing the existing
> > text ("It does not make sense to use this feature with a non-static
> > local variable since such variables do not have assembler names.") with
> > "Do not use this feature with a non-static local variable." or maybe "It
> > is not supported to use this feature with a non-static local variable
> > since such variables do not have assembler names."
> "You cannot use this feature ..." etc.?  Keep the part about not having
> assembler names, it is useful.

Due to the quirks of the English language, I'm not sure 'cannot' is the 
right word here.  More correct would be 'cannot reliably' but I don't 
want to be that wishy-washy.

And I'm a little iffy about the 'since such variables do not have 
assembler names,' as it seemed a bit bold to make assertions about the 
implementation details for all assemblers (past, present and future) for 
all platforms.  But you are right, it does convey a bit of the 'why' for 
this limitation, so keeping it is a good idea.  How about:

"gcc does not support using this feature with a non-static local 
variable since typically such variables do not have assembler names."

BTW, the trick for getting the "ignoring asm-specifier for non-static 
local variable" message was renaming my file from sta5.cpp to sta5.c.  
Seems like this should apply to both, but whatever.

> > > The first part ("must not use a register name") is an important warning.
> > Clarifying this is a good idea.  Although limiting it to only saying
> > "don't use register names" seems a little, well, limiting. Who knows
> > what kind of offsets or asm qualifiers they might try to cram in here?
> Register names is the common case to hurt you...  "r0" etc. ;-)

But as we have seen (%gs:4), people are willing to try other things.  
And rather than try to list all the things that don't work (register, 
registers with offsets, etc), I'm hoping we can find a way to specify 
the one thing that is supported.

> > How about:
> >
> > "Only label names valid for your assembler are permitted within the asm."
> The assembler calls it "symbol names" (labels end in a colon).  But it
> won't help: e.g. "r0" is a perfectly fine name for the assembler, too!
>
> It should say something like "if the string you put here is seen as
> something else than a symbol name by the assembler, anywhere the compiler
> puts it, you're on your own", but that is pretty vague as well.

Ok, how about "Only symbol names that define labels are permitted within 
the asm."

A bit awkward, but I believe it conveys the intent.

> You forgot to make it "register", so it is not a register variable.

Ahh, true.  I suppose we could say something about don't use 'register' 
with 'asm labels', but it doesn't seem worth the effort.

dw