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From: bailey@jacobs.CS.ORST.EDU (Kirk Bailey)
Newsgroups: comp.sys.transputer
Subject: Re: Transputer C compiler efficiency - results (long)
Message-ID: <bailey.661782689@jacobs.CS.ORST.EDU>
Date: 21 Dec 90 12:31:29 GMT
References: <JEREMY.90Dec20211502@chook.ua.oz.au>
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Dear Net Community, 
 
	I'm posting in response to the recent (excellent), "C" compiler review
by Jeremy Webber.  I wanted to mention a technique which may be used with the
current (V89.1), Logical Systems "C" compiler to implement stack bounds
checking (and the like):
 
Write a small "C" function such as:
 
void
stack_check(int dummy)
	{
	if(((char *) ((&dummy) + 3)) < BOTTOM_OF_STACK)
		{
		printf("Stack Underflow\n");
		exit(1);
		}
	}
 
Where BOTTOM_OF_STACK is the desired stack minimum address.
 
	After compiling this routine it may be linked in with the application
code and calls to it inserted automatically by using the "-ti" TCX command
flag (see TCX manual for detailed information).  The same technique may be used
to implement a function trace-in/trace-out facility:
 
void
trace_in(int ws_size)
	{
	printf("Trace entry of function starting near %p\n",
		*((&ws_size) - 1));
	printf("\tFunction needs %u word(s) of workspace (current WS = %p)\n",
		ws_size,(&ws_size) + 3);
	}
 
void
trace_out(int dummy)
	{
	printf("Trace exit of function ending near %p\n",*((&dummy) - 1));
	}
 
	Note that calls to "trace_in" would again be inserted with the TCX
"-ti" option while calls to "trace_out" would require the "-to" option.
 
	In the "REAL SOON NOW" category: the upcoming version of the Logical
Systems "C" package has a more automatic way to accomplish stack underflow
checking (plus addressing many of the other concerns the review mentioned).
As I'm sure is the case with the other vendors, we welcome feedback and ideas
of what should be changed in the future, whether in the form of a comprehensive
review or just a quick EMAIL note.  Keep the cards and bricks coming...
 
	Hope everyone has a excellent new year!
 
		Cheers,
			Kirk Bailey
			Logical Systems