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Source file src/cmd/internal/obj/pass.go

Documentation: cmd/internal/obj

  // Inferno utils/6l/pass.c
  // https://bitbucket.org/inferno-os/inferno-os/src/default/utils/6l/pass.c
  //
  //	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
  //	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
  //	Portions Copyright © 1997-1999 Vita Nuova Limited
  //	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
  //	Portions Copyright © 2004,2006 Bruce Ellis
  //	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
  //	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
  //	Portions Copyright © 2009 The Go Authors. All rights reserved.
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  // THE SOFTWARE.
  
  package obj
  
  // Code and data passes.
  
  // brloop returns the ultimate destination of the series of unconditional jumps beginning at p.
  // In the case of an infinite loop, brloop returns nil.
  func brloop(p *Prog) *Prog {
  	c := 0
  	for q := p; q != nil; q = q.Pcond {
  		if q.As != AJMP || q.Pcond == nil {
  			return q
  		}
  		c++
  		if c >= 5000 {
  			// infinite loop
  			return nil
  		}
  	}
  	panic("unreachable")
  }
  
  // checkaddr checks that a has an expected encoding, especially TYPE_CONST vs TYPE_ADDR.
  func checkaddr(ctxt *Link, p *Prog, a *Addr) {
  	switch a.Type {
  	case TYPE_NONE, TYPE_REGREG2, TYPE_REGLIST:
  		return
  
  	case TYPE_BRANCH, TYPE_TEXTSIZE:
  		if a.Reg != 0 || a.Index != 0 || a.Scale != 0 || a.Name != 0 {
  			break
  		}
  		return
  
  	case TYPE_MEM:
  		return
  
  	case TYPE_CONST:
  		// TODO(rsc): After fixing SHRQ, check a.Index != 0 too.
  		if a.Name != 0 || a.Sym != nil || a.Reg != 0 {
  			ctxt.Diag("argument is TYPE_CONST, should be TYPE_ADDR, in %v", p)
  			return
  		}
  
  		if a.Reg != 0 || a.Scale != 0 || a.Name != 0 || a.Sym != nil || a.Val != nil {
  			break
  		}
  		return
  
  	case TYPE_FCONST, TYPE_SCONST:
  		if a.Reg != 0 || a.Index != 0 || a.Scale != 0 || a.Name != 0 || a.Offset != 0 || a.Sym != nil {
  			break
  		}
  		return
  
  	case TYPE_REG:
  		// TODO(rsc): After fixing PINSRQ, check a.Offset != 0 too.
  		// TODO(rsc): After fixing SHRQ, check a.Index != 0 too.
  		if a.Scale != 0 || a.Name != 0 || a.Sym != nil {
  			break
  		}
  		return
  
  	case TYPE_ADDR:
  		if a.Val != nil {
  			break
  		}
  		if a.Reg == 0 && a.Index == 0 && a.Scale == 0 && a.Name == 0 && a.Sym == nil {
  			ctxt.Diag("argument is TYPE_ADDR, should be TYPE_CONST, in %v", p)
  		}
  		return
  
  	case TYPE_SHIFT, TYPE_REGREG:
  		if a.Index != 0 || a.Scale != 0 || a.Name != 0 || a.Sym != nil || a.Val != nil {
  			break
  		}
  		return
  
  	case TYPE_INDIR:
  		// Expect sym and name to be set, nothing else.
  		// Technically more is allowed, but this is only used for *name(SB).
  		if a.Reg != 0 || a.Index != 0 || a.Scale != 0 || a.Name == 0 || a.Offset != 0 || a.Sym == nil || a.Val != nil {
  			break
  		}
  		return
  	}
  
  	ctxt.Diag("invalid encoding for argument %v", p)
  }
  
  func linkpatch(ctxt *Link, sym *LSym, newprog ProgAlloc) {
  	var c int32
  	var name string
  	var q *Prog
  
  	for p := sym.Func.Text; p != nil; p = p.Link {
  		checkaddr(ctxt, p, &p.From)
  		if p.From3 != nil {
  			checkaddr(ctxt, p, p.From3)
  		}
  		checkaddr(ctxt, p, &p.To)
  
  		if ctxt.Arch.Progedit != nil {
  			ctxt.Arch.Progedit(ctxt, p, newprog)
  		}
  		if p.To.Type != TYPE_BRANCH {
  			continue
  		}
  		if p.To.Val != nil {
  			// TODO: Remove To.Val.(*Prog) in favor of p->pcond.
  			p.Pcond = p.To.Val.(*Prog)
  			continue
  		}
  
  		if p.To.Sym != nil {
  			continue
  		}
  		c = int32(p.To.Offset)
  		for q = sym.Func.Text; q != nil; {
  			if int64(c) == q.Pc {
  				break
  			}
  			if q.Forwd != nil && int64(c) >= q.Forwd.Pc {
  				q = q.Forwd
  			} else {
  				q = q.Link
  			}
  		}
  
  		if q == nil {
  			name = "<nil>"
  			if p.To.Sym != nil {
  				name = p.To.Sym.Name
  			}
  			ctxt.Diag("branch out of range (%#x)\n%v [%s]", uint32(c), p, name)
  			p.To.Type = TYPE_NONE
  		}
  
  		p.To.Val = q
  		p.Pcond = q
  	}
  
  	if !ctxt.Flag_optimize {
  		return
  	}
  
  	// Collapse series of jumps to jumps.
  	for p := sym.Func.Text; p != nil; p = p.Link {
  		if p.Pcond == nil {
  			continue
  		}
  		p.Pcond = brloop(p.Pcond)
  		if p.Pcond != nil && p.To.Type == TYPE_BRANCH {
  			p.To.Offset = p.Pcond.Pc
  		}
  	}
  }
  

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