Just comment.

Jason R Thorpe writes:
> Attached is a patch to make the kernel directly invoke a signal handler,
> rather than bouncing through the signal trampoline.  Now, the trampoline
> is used only to return from the signal.  The net result is to save a few
> instructions during signal delivery.

The pointer to "struct sigcontext" already in sigframe when sending
a signal, and we can reuse it.
This saves 6 bytes in the trampoline.

> 		signal context structure
> 	------------------------------------------------------------
> 		pointer to sigcontext structure			[12]
> 		signal specific code				[8]
> 		signal number					[4]
> 	SP->	return address (address of signal trampoline)	[0]

Data structure description in decreasing address order is
rather too hard to read (to me). :)


Suggested sigcode:

/*
 * Signal trampoline; copied to top of user stack.
 *
 * The handler has returned here as if we had called it.  On
 * entry, the stack looks like:
 *
 *	sp+0	->	signal number
 *	sp+4		signal specific code
 *	sp+8		pointer to signal context frame (scp)
 *	sp+12		saved hardware state
 *			(including signal context frame)
 *				.
 *				.
 *				.
 */

	.data
	.align	2
GLOBAL(sigcode)
	addql	#4,%sp		| pop signal number		(2 bytes)
	trap	#3		| special sigreturn trap	(2 bytes)
	movl	%d0,%sp@(4)	| save errno			(4 bytes)
	moveq	#SYS_exit,%d0	| syscall == exit		(2 bytes)
	trap	#0		| exit(errno)			(2 bytes)
	.align	2
GLOBAL(esigcode)