New unit

Fix long-standing stack scan problems

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 Change: 18680
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mps/src/sssos8.s

@@ -0,0 +1,43 @@
+!  impl.s.sssos8
+!
+!                      STACK SCANNING
+!
+!  $HopeName: MMsrc!sssos9sc.S(trunk.1) $
+!
+!  Copyright (C) 1995 Harlequin Group, all rights reserved
+!
+!  This scans the stack and the preserved integer registers.
+!  See design.mps.thread-manager
+!
+!  This file is identical to impl.s.sssus8, except for the
+!  leading underscore convention on C names.  They should be
+!  changed in parallel.
+!
+!  The non-global registers are preserved into the stackframe
+!  by the "ta 3" instruction.  This leaves the global registers.
+!  According to the Sparc Architecture Manual:
+!  %g1 is assumed to be volatile across procedure calls
+!  %g2...%g4 are "reserved for use by application programmer"
+!  %g5...%g7 are "nonvolatile and reserved for (as-yet-undefined)
+!     use by the execution environment"
+!  To be safe %g2 to %g7 are pushed onto the stack before scanning
+!  it just in case.
+
+.text
+  .align 4
+  .global StackScan
+StackScan:                !(ss, stackBot)
+  save %sp,-120,%sp       !23 required + 6 globals = 29 words, 8-aligned
+
+  std %g6,[%fp-8]         !double stores
+  std %g4,[%fp-16]
+  std %g2,[%fp-24]
+  ta 3                    !flushes register windows onto stack
+
+  mov %i0,%o0             !ss
+  sub %fp,24,%o1          !stackTop (base)
+  call TraceScanArea      !(stackTop,stackBot,trace,rank) returns e
+  mov %i1,%o2          !ds!stackBot (limit)
+
+  ret
+  restore %g0,%o0,%o0  !ds!return e