Re: C compiler, assembler and linker

[mjn3@codepoet.org (Manuel Novoa III)]

Hello Robert,

On Tue, Jul 23, 2002 at 12:26:52AM +0100, Robert de Bath wrote:
> On Mon, 15 Jul 2002, Manuel Novoa III wrote:
> > 3) Support asm() at file scope.  This is to allow the equivalent
> >    of #asm/#endasm in macros.
> 
> Hmm, interesting, I'll have to look at this ... carefully.

I mainly use this for defining aliases for functions.  For example,
in an object file for the labs function I could write

#define strong_alias(Y,X)      asm("export _" "X" "\n_" "X" " = _" "Y");

strong_alias(labs,imaxabs)

long int labs(long int j)
{
	return (j >= 0) ? j : -j;
}

which would make imaxabs an alias for labs (at least when optimizing).

I also use this with bcc auto-run functions.  I'm sure you'll recognize
the following.  Allowing asm() at file scope, I can hide the implementation
details with a macro where I couldn't with #asm/#endasm.

#ifdef __AS386_16__
#define __BCC_CTOR(X) asm( \
"  loc  1\n"         /* Make sure the pointer is in the correct segment */ \
"auto_func:\n"       /* Label for bcc -M to work. */ \
".word  _" "X" "\n"  /* Pointer to the autorun function */ \
".word no_op\n"      /* Space filler cause segs are padded to 4 bytes. */ \
".text\n"            /* So the function after is also in the correct seg. */ \
)
#endif

#ifdef __AS386_32__
#define __BCC_CTOR(X) asm( \
"  loc  1\n"         /* Make sure the pointer is in the correct segment */ \
"auto_func:\n"       /* Label for bcc -M to work. */ \
".long  _" "X" "\n"  /* Pointer to the autorun function */ \
".text\n"            /* So the function after is also in the correct seg. */ \
)
#endif

> > 4) Limited support for things like "#define stdio stdio".  Stock bcc
> >    goes into an infinite loop when encounting this.  The implementation
> >    has flaws, but it does what I needed.  You see this a lot in the
> >    glibc headers we're using with uClibc (yes I'm working on a port).
> 
> I don't like the way this is done; I think it'd be better to 'smudge'
> the definition of the current macro so that the search can't find the
> word for recursion.

I don't like the way it is done either... but it was quick and it
allowed me to avoid special-casing lots of uClibc (glibc) headers.

> > 5) Improved condition wrapping of the floating point related code in
> >    the bcc source (working towards building bcc for elks).  As I said,
> >    the code generator dies... at least using elksemu.
> 
> I'd suspect the dtype or fltype variables.

I still haven't had time to investigate this.  :-(

Manuel