Re: Question about genassym, locore.s and 0-sized arrays (showstopper for an icc compiled kernel)

From: Marcel Moolenaar <>
Date: Thu, 4 Sep 2003 15:47:09 -0700
On Fri, Sep 05, 2003 at 12:14:11AM +0200, Alexander Leidinger wrote:
> On Thu, 4 Sep 2003 11:28:58 -0500
> Dan Nelson <> wrote:
> > If you're talking FreeBSD 5, you should be able to simply subsitute a
> > C99 "flexible array member" (basically replace "[0]" with "[]") and get
> > the same effect.  0-length arrays are a gcc extension:
> > 
> >
> > 
> > Under FreeBSD 4.x, you can't use them because gcc 2.95 only supports
> > the gcc extension.  Intel has added support for a lot of gcc extensions
> > recently; they may be willing to add this to the list.
> Please read my mail again, icc already supports my_array[0], but the
> resulting array in the binary has size '1'. The actual showstopper is
> the output of To me it seems it's just a issue,
> but I don't really know what's going on in the kernel, so I ask here.

We use the size of the symbol (ie the size of the object identified
by the symbol) to pass around values. This we do by creating arrays.
If we want to export a C constant 'FOOBAR' to assembly and the constant
is defined to be 6, then we create an array for the sign, of which the
size is 1 for negative numbers and 0 otherwise. In this case the array
will be named FOOBARsign and its size is 0. We also create 4 arrays (*w0,
*w1, *w2 and *w3), each with a maximum of 64K and corresponding to the
4 16-bit words that constitutes a single 64-bit entity.
In this case
	00000006 C FOOBARw0
	00000000 C FOOBARw1
	00000000 C FOOBARw2
	00000000 C FOOBARw3

If the compiler creates arrays of size 1 for arrays we define as a
zero-sized array, you get exactly what you've observed.

 Marcel Moolenaar	  USPA: A-39004
Received on Thu Sep 04 2003 - 13:47:22 UTC

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