Exemplo n.º 1
0
func progedit(ctxt *liblink.Link, p *liblink.Prog) {
	var literal string
	var s *liblink.LSym
	var q *liblink.Prog
	// Thread-local storage references use the TLS pseudo-register.
	// As a register, TLS refers to the thread-local storage base, and it
	// can only be loaded into another register:
	//
	//         MOVQ TLS, AX
	//
	// An offset from the thread-local storage base is written off(reg)(TLS*1).
	// Semantically it is off(reg), but the (TLS*1) annotation marks this as
	// indexing from the loaded TLS base. This emits a relocation so that
	// if the linker needs to adjust the offset, it can. For example:
	//
	//         MOVQ TLS, AX
	//         MOVQ 8(AX)(TLS*1), CX // load m into CX
	//
	// On systems that support direct access to the TLS memory, this
	// pair of instructions can be reduced to a direct TLS memory reference:
	//
	//         MOVQ 8(TLS), CX // load m into CX
	//
	// The 2-instruction and 1-instruction forms correspond roughly to
	// ELF TLS initial exec mode and ELF TLS local exec mode, respectively.
	//
	// We applies this rewrite on systems that support the 1-instruction form.
	// The decision is made using only the operating system (and probably
	// the -shared flag, eventually), not the link mode. If some link modes
	// on a particular operating system require the 2-instruction form,
	// then all builds for that operating system will use the 2-instruction
	// form, so that the link mode decision can be delayed to link time.
	//
	// In this way, all supported systems use identical instructions to
	// access TLS, and they are rewritten appropriately first here in
	// liblink and then finally using relocations in the linker.
	if canuselocaltls(ctxt) {
		// Reduce TLS initial exec model to TLS local exec model.
		// Sequences like
		//	MOVQ TLS, BX
		//	... off(BX)(TLS*1) ...
		// become
		//	NOP
		//	... off(TLS) ...
		//
		// TODO(rsc): Remove the Hsolaris special case. It exists only to
		// guarantee we are producing byte-identical binaries as before this code.
		// But it should be unnecessary.
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Typ == D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_R15 && ctxt.Headtype != liblink.Hsolaris {
			nopout(p)
		}
		if p.From.Index == D_TLS && D_INDIR+D_AX <= p.From.Typ && p.From.Typ <= D_INDIR+D_R15 {
			p.From.Typ = D_INDIR + D_TLS
			p.From.Scale = 0
			p.From.Index = D_NONE
		}
		if p.To.Index == D_TLS && D_INDIR+D_AX <= p.To.Typ && p.To.Typ <= D_INDIR+D_R15 {
			p.To.Typ = D_INDIR + D_TLS
			p.To.Scale = 0
			p.To.Index = D_NONE
		}
	} else {
		// As a courtesy to the C compilers, rewrite TLS local exec load as TLS initial exec load.
		// The instruction
		//	MOVQ off(TLS), BX
		// becomes the sequence
		//	MOVQ TLS, BX
		//	MOVQ off(BX)(TLS*1), BX
		// This allows the C compilers to emit references to m and g using the direct off(TLS) form.
		if (p.As == AMOVQ || p.As == AMOVL) && p.From.Typ == D_INDIR+D_TLS && D_AX <= p.To.Typ && p.To.Typ <= D_R15 {
			q = liblink.Appendp(ctxt, p)
			q.As = p.As
			q.From = p.From
			q.From.Typ = D_INDIR + p.To.Typ
			q.From.Index = D_TLS
			q.From.Scale = 2 // TODO: use 1
			q.To = p.To
			p.From.Typ = D_TLS
			p.From.Index = D_NONE
			p.From.Offset = 0
		}
	}
	// TODO: Remove.
	if ctxt.Headtype == liblink.Hwindows || ctxt.Headtype == liblink.Hplan9 {
		if p.From.Scale == 1 && p.From.Index == D_TLS {
			p.From.Scale = 2
		}
		if p.To.Scale == 1 && p.To.Index == D_TLS {
			p.To.Scale = 2
		}
	}
	if ctxt.Headtype == liblink.Hnacl {
		nacladdr(ctxt, p, &p.From)
		nacladdr(ctxt, p, &p.To)
	}
	// Maintain information about code generation mode.
	if ctxt.Mode == 0 {
		ctxt.Mode = 64
	}
	p.Mode = ctxt.Mode
	switch p.As {
	case AMODE:
		if p.From.Typ == D_CONST || p.From.Typ == D_INDIR+D_NONE {
			switch int(p.From.Offset) {
			case 16,
				32,
				64:
				ctxt.Mode = int(p.From.Offset)
				break
			}
		}
		nopout(p)
		break
	}
	// Rewrite CALL/JMP/RET to symbol as D_BRANCH.
	switch p.As {
	case ACALL,
		AJMP,
		ARET:
		if (p.To.Typ == D_EXTERN || p.To.Typ == D_STATIC) && p.To.Sym != nil {
			p.To.Typ = D_BRANCH
		}
		break
	}
	// Rewrite float constants to values stored in memory.
	switch p.As {
	case AFMOVF,
		AFADDF,
		AFSUBF,
		AFSUBRF,
		AFMULF,
		AFDIVF,
		AFDIVRF,
		AFCOMF,
		AFCOMFP,
		AMOVSS,
		AADDSS,
		ASUBSS,
		AMULSS,
		ADIVSS,
		ACOMISS,
		AUCOMISS:
		if p.From.Typ == D_FCONST {
			var i32 uint32
			var f32 float32
			f32 = float32(p.From.U.Dval)
			i32 = math.Float32bits(f32)
			literal = fmt.Sprintf("$f32.%08x", uint32(i32))
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Typ == 0 {
				s.Typ = liblink.SRODATA
				liblink.Adduint32(ctxt, s, i32)
				s.Reachable = 0
			}
			p.From.Typ = D_EXTERN
			p.From.Sym = s
			p.From.Offset = 0
		}
	case AFMOVD,
		AFADDD,
		AFSUBD,
		AFSUBRD,
		AFMULD,
		AFDIVD,
		AFDIVRD,
		AFCOMD,
		AFCOMDP,
		AMOVSD,
		AADDSD,
		ASUBSD,
		AMULSD,
		ADIVSD,
		ACOMISD,
		AUCOMISD:
		if p.From.Typ == D_FCONST {
			var i64 uint64
			i64 = math.Float64bits(p.From.U.Dval)
			literal = fmt.Sprintf("$f64.%016x", uint64(i64))
			s = liblink.Linklookup(ctxt, literal, 0)
			if s.Typ == 0 {
				s.Typ = liblink.SRODATA
				liblink.Adduint64(ctxt, s, i64)
				s.Reachable = 0
			}
			p.From.Typ = D_EXTERN
			p.From.Sym = s
			p.From.Offset = 0
		}
		break
	}
}