🚀 go-pugleaf

Subject: save 4 bytes of text in sigvec.s
Index:	lib/libc/pdp/sys/sigvec.s 2.10BSD

Description:
	The stack cleanup logic did not take advantage of the fact that
	"mov (sp)+, (sp)" does not affect the carry bit.  By taking
	advantage of the pdp-11s architecture set 4 bytes of I-space
	may be conserved.

Repeat-By:
	Observation, i.e. RTFS.

Fix:
	Apply the following patch:
*** sigvec.s.old	Thu Jan 29 05:52:42 1987
--- sigvec.s	Fri Sep 22 22:31:38 1989
***************
*** 31,43 ****
  	mov	(sp),-(sp)	/ push return address down one place
  	mov	$sigtramp,2(sp)	/   to leave a space for the address of
  	SYS(sigvec)		/   sigtramp
- 	bes	1f
  	mov	(sp)+,(sp)	/ (clean up stack)
! 	rts	pc
! 1:
! 	mov	(sp)+,(sp)	/ (clean up stack)
  	mov	r0,_errno
  	mov	$-1,r0
  	rts	pc
  
  /*
--- 31,41 ----
  	mov	(sp),-(sp)	/ push return address down one place
  	mov	$sigtramp,2(sp)	/   to leave a space for the address of
  	SYS(sigvec)		/   sigtramp
  	mov	(sp)+,(sp)	/ (clean up stack)
! 	bec	1f
  	mov	r0,_errno
  	mov	$-1,r0
+ 1:
  	rts	pc
  
  /*