Re: making aliases into the middle of a structure

[Zack Weinberg <zack@rabi.columbia.edu>]

On Fri, 23 Apr 1999 00:14:34 -0600, Jeffrey A Law wrote:
>
>  In message < org15s33hj.fsf@lua.lbi.dcc.unicamp.br >you write:
>  > > Because the preprocessor can't compute offsetof() all the way down;
>  > > I'd have to compile and run a test program.  Which loses when
>  > > cross-compiling.
>  > 
>  > Well, you could try to extract this information from the assembly
>  > code, or from some RTL dump (since you're bound to gcc anyway), but I
>  > wouldn't like to be the one to implement it :-)
>Cygnus implemented a switch to have the compiler dump offsets for fields
>within structures in a format intended to be used by assembly code.
>
>It's not something we've used a lot and haven't ever thought it worth
>the effort to clean it up and submit it to egcs.

This is a cute idea, and I could think of uses in libc, but it doesn't
really solve my current problem (without excessive magic).  I'd much
rather be able to write

extern int var __attribute__ ((alias (structure.field)));

which is what the patch I sent yesterday implements.

Incidentally, I found what I think is a GAS bug: it forgets
aliases to symbols allocated with .comm.  For example:

int common;
extern int alias __attribute__ ((alias("common")));

`alias' will not be defined in the object file.  The assembly dump
looks correct to me.

zw