Char *Foo = "ABC" or Char Foo[] = "ABC"" ?

[Richard Henderson]

On Fri, Oct 07, 2005 at 07:06:21PM +0100, Felix Oxley wrote:
> > For variables marked __initdata, the "*foo" form causes only the
> > pointer, not the string itself, to be dropped from the kernel image,
> > which is a bug.

Not a bug.  A missing feature, perhaps, but not a bug.

> > http://lists.osdl.org/pipermail/kernel-janitors/2005-May/004146.html

He did something wrong.  The size numbers he gives are obviously
wrong -- the data field is 0 in cases that cannot be true.  I don't
replicate his results either.  E.g.

   text    data     bss     dec     hex filename
     11       8       0      19      13 s1.o
      0      11       0      11       b s2.o

That said, some ABIs over-align arrays, and so you might get more
padding with arrays than raw strings.  But it'll be less than the
size of an extra pointer variable.

> The second part of the task was descibed thus:
> > 2) "unsigned int" is preferred to "int", it generates better asm code on
> > all platforms except sh5.  This replacement needs to be done manually,
> > because often 'int' is required due to negative values -Exxx commonly
> > passed as error values.
> 
> Can anyone comment on the accuracy of this?

Definitely false for mips and alpha, so I really doubt the accuracy
of their survey of all platforms.  My guess is that it allows for the
possibility of better code for x86_64 (but is not totally realized;
there's a large outstanding gcc patch that attempts to fix this), but
is mostly a wash elsewhere.


r~