// Convert the direct jump relocation r to refer to a trampoline if the target is too far
func trampoline(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol) {
switch r.Type {
case obj.R_CALLARM:
// r.Add is the instruction
// low 24-bit encodes the target address
t := (ld.Symaddr(r.Sym) + int64(signext24(r.Add&0xffffff)*4) - (s.Value + int64(r.Off))) / 4
if t > 0x7fffff || t < -0x800000 || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
// direct call too far, need to insert trampoline
offset := (signext24(r.Add&0xffffff) + 2) * 4
var tramp *ld.Symbol
for i := 0; ; i++ {
name := r.Sym.Name + fmt.Sprintf("%+d-tramp%d", offset, i)
tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
if tramp.Value == 0 {
// either the trampoline does not exist -- we need to create one,
// or found one the address which is not assigned -- this will be
// laid down immediately after the current function. use this one.
break
}
t = (ld.Symaddr(tramp) - 8 - (s.Value + int64(r.Off))) / 4
if t >= -0x800000 && t < 0x7fffff {
// found an existing trampoline that is not too far
// we can just use it
break
}
}
if tramp.Type == 0 {
// trampoline does not exist, create one
ctxt.AddTramp(tramp)
tramp.Size = 12 // 3 instructions
tramp.P = make([]byte, tramp.Size)
t = ld.Symaddr(r.Sym) + int64(offset)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe12fff10 | 11) // JMP (R11)
o3 := uint32(t) // WORD $target
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
}
// modify reloc to point to tramp, which will be resolved later
r.Sym = tramp
r.Add = r.Add&0xff000000 | 0xfffffe // clear the offset embedded in the instruction
r.Done = 0
}
default:
ld.Errorf(s, "trampoline called with non-jump reloc: %v", r.Type)
}
}
// generate a trampoline to target+offset in position independent code
func gentramppic(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 16 // 4 instructions
tramp.P = make([]byte, tramp.Size)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 4) // MOVW 4(R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
o3 := uint32(0xe12fff10 | 11) // JMP (R11)
o4 := uint32(0) // WORD $(target-pc) // filled in with relocation
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
r := ld.Addrel(tramp)
r.Off = 12
r.Type = obj.R_PCREL
r.Siz = 4
r.Sym = target
r.Add = offset + 4
}
// generate a trampoline to target+offset
func gentramp(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 12 // 3 instructions
tramp.P = make([]byte, tramp.Size)
t := ld.Symaddr(target) + int64(offset)
o1 := uint32(0xe5900000 | 11<<12 | 15<<16) // MOVW (R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe12fff10 | 11) // JMP (R11)
o3 := uint32(t) // WORD $target
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
if ld.Linkmode == ld.LinkExternal {
r := ld.Addrel(tramp)
r.Off = 8
r.Type = obj.R_ADDR
r.Siz = 4
r.Sym = target
r.Add = offset
}
}
// generate a trampoline to target+offset in dynlink mode (using GOT)
func gentrampdyn(tramp, target *ld.Symbol, offset int64) {
tramp.Size = 20 // 5 instructions
o1 := uint32(0xe5900000 | 11<<12 | 15<<16 | 8) // MOVW 8(R15), R11 // R15 is actual pc + 8
o2 := uint32(0xe0800000 | 11<<12 | 15<<16 | 11) // ADD R15, R11, R11
o3 := uint32(0xe5900000 | 11<<12 | 11<<16) // MOVW (R11), R11
o4 := uint32(0xe12fff10 | 11) // JMP (R11)
o5 := uint32(0) // WORD $target@GOT // filled in with relocation
o6 := uint32(0)
if offset != 0 {
// insert an instruction to add offset
tramp.Size = 24 // 6 instructions
o6 = o5
o5 = o4
o4 = uint32(0xe2800000 | 11<<12 | 11<<16 | immrot(uint32(offset))) // ADD $offset, R11, R11
o1 = uint32(0xe5900000 | 11<<12 | 15<<16 | 12) // MOVW 12(R15), R11
}
tramp.P = make([]byte, tramp.Size)
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
ld.SysArch.ByteOrder.PutUint32(tramp.P[16:], o5)
if offset != 0 {
ld.SysArch.ByteOrder.PutUint32(tramp.P[20:], o6)
}
r := ld.Addrel(tramp)
r.Off = 16
r.Type = obj.R_GOTPCREL
r.Siz = 4
r.Sym = target
r.Add = 8
if offset != 0 {
// increase reloc offset by 4 as we inserted an ADD instruction
r.Off = 20
r.Add = 12
}
}
// resolve direct jump relocation r in s, and add trampoline if necessary
func trampoline(ctxt *ld.Link, r *ld.Reloc, s *ld.Symbol) {
t := ld.Symaddr(r.Sym) + r.Add - (s.Value + int64(r.Off))
switch r.Type {
case obj.R_CALLPOWER:
// If branch offset is too far then create a trampoline.
if int64(int32(t<<6)>>6) != t || (*ld.FlagDebugTramp > 1 && s.File != r.Sym.File) {
var tramp *ld.Symbol
for i := 0; ; i++ {
// Using r.Add as part of the name is significant in functions like duffzero where the call
// target is at some offset within the function. Calls to duff+8 and duff+256 must appear as
// distinct trampolines.
name := r.Sym.Name
if r.Add == 0 {
name = name + fmt.Sprintf("-tramp%d", i)
} else {
name = name + fmt.Sprintf("%+x-tramp%d", r.Add, i)
}
// Look up the trampoline in case it already exists
tramp = ctxt.Syms.Lookup(name, int(r.Sym.Version))
if tramp.Value == 0 {
break
}
t = ld.Symaddr(tramp) + r.Add - (s.Value + int64(r.Off))
// If the offset of the trampoline that has been found is within range, use it.
if int64(int32(t<<6)>>6) == t {
break
}
}
if tramp.Type == 0 {
ctxt.AddTramp(tramp)
tramp.Size = 16 // 4 instructions
tramp.P = make([]byte, tramp.Size)
t = ld.Symaddr(r.Sym) + r.Add
f := t & 0xffff0000
o1 := uint32(0x3fe00000 | (f >> 16)) // lis r31,trampaddr hi (r31 is temp reg)
f = t & 0xffff
o2 := uint32(0x63ff0000 | f) // ori r31,trampaddr lo
o3 := uint32(0x7fe903a6) // mtctr
o4 := uint32(0x4e800420) // bctr
ld.SysArch.ByteOrder.PutUint32(tramp.P, o1)
ld.SysArch.ByteOrder.PutUint32(tramp.P[4:], o2)
ld.SysArch.ByteOrder.PutUint32(tramp.P[8:], o3)
ld.SysArch.ByteOrder.PutUint32(tramp.P[12:], o4)
}
r.Sym = tramp
r.Add = 0 // This was folded into the trampoline target address
r.Done = 0
}
default:
ld.Errorf(s, "trampoline called with non-jump reloc: %v", r.Type)
}
}