Message-Id: <200002260336.WAA05805@delorie.com>
From: "Richard Poole" <richard AT hjpent DOT force9 DOT co DOT uk>
To: <djgpp AT delorie DOT com>
Subject: Compiling a function to raw executable code.
Date: Sat, 26 Feb 2000 03:40:38 -0000
X-MSMail-Priority: Normal
X-Priority: 3
X-Mailer: Microsoft Internet Mail 4.70.1155
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Reply-To: djgpp AT delorie DOT com

Is it possible for me to use GCC to compile a function to raw machine
code and nothing else (i.e. no run-time engine, no DMPI server etc.)?

I am writing a modular audio synthesiser that opens all files ending in
a certain extension and copies their contents into allocated memory.
These files (otherwise known as devices) should contain raw executable
code, and I need the main program to be able to call that code. In the
main program there is an array of pointers to the devices that it has
loaded into memory, like this...

-------- start --------
typedef struct DEVICE_STRUCT
{
	...
	void (*code)(unsigned int *,unsigned int *);
} DEVICE_STRUCT;

struct DEVICE_STRUCT device[1024];
-------- end --------

Some of the functions that will be called are too complicated to write
in assembler, so it would be very useful to be able to write them in C,
like this...

-------- start --------
void half_volume(unsigned int *inports[256],unsigned int
*outports[256])
{
	outports[0]=inports[0]>>1;
	return;
}
-------- end --------

Clearly a grossly simplified example of a near useless piece of audio
equipement, but hopefully it demonstrates my point. How could I get GCC
to compile that function so that the executable it generates contains
only the compiled code within that function (i.e.
outports[0]=inports[0]>>1; return;) so I can load it into allocated
memory and call it?

Say device[0].code is pointing to the allocated memory that the code of
half_volume has been loaded into.

-------- start --------
int inports[256],outports[256];
inports[0]=32768;
device[0].code(inports,outports);
-------- end --------

At this point, outports[0] should be equal to 16384. Hopefully that
helped you understand the problem if you didn't before, otherwise it's
probably just confussed everyone, but please mail me if you have any
insight into the problem.

Many thanks,
Richard Poole.