// appendPCDeltaCFA appends per-PC CFA deltas to b and returns the final slice.
func appendPCDeltaCFA(b []byte, deltapc, cfa int64) []byte {
b = append(b, dwarf.DW_CFA_def_cfa_offset_sf)
b = dwarf.AppendSleb128(b, cfa/dataAlignmentFactor)
switch {
case deltapc < 0x40:
b = append(b, uint8(dwarf.DW_CFA_advance_loc+deltapc))
case deltapc < 0x100:
b = append(b, dwarf.DW_CFA_advance_loc1)
b = append(b, uint8(deltapc))
case deltapc < 0x10000:
b = append(b, dwarf.DW_CFA_advance_loc2)
b = Thearch.Append16(b, uint16(deltapc))
default:
b = append(b, dwarf.DW_CFA_advance_loc4)
b = Thearch.Append32(b, uint32(deltapc))
}
return b
}
func writeframes(ctxt *Link, syms []*Symbol) []*Symbol {
var dwarfctxt dwarf.Context = dwctxt{ctxt}
if framesec == nil {
framesec = Linklookup(ctxt, ".debug_frame", 0)
}
framesec.Type = obj.SDWARFSECT
framesec.R = framesec.R[:0]
fs := framesec
syms = append(syms, fs)
// Emit the CIE, Section 6.4.1
cieReserve := uint32(16)
if haslinkregister(ctxt) {
cieReserve = 32
}
Adduint32(ctxt, fs, cieReserve) // initial length, must be multiple of thearch.ptrsize
Adduint32(ctxt, fs, 0xffffffff) // cid.
Adduint8(ctxt, fs, 3) // dwarf version (appendix F)
Adduint8(ctxt, fs, 0) // augmentation ""
dwarf.Uleb128put(dwarfctxt, fs, 1) // code_alignment_factor
dwarf.Sleb128put(dwarfctxt, fs, dataAlignmentFactor) // all CFI offset calculations include multiplication with this factor
dwarf.Uleb128put(dwarfctxt, fs, int64(Thearch.Dwarfreglr)) // return_address_register
Adduint8(ctxt, fs, dwarf.DW_CFA_def_cfa) // Set the current frame address..
dwarf.Uleb128put(dwarfctxt, fs, int64(Thearch.Dwarfregsp)) // ...to use the value in the platform's SP register (defined in l.go)...
if haslinkregister(ctxt) {
dwarf.Uleb128put(dwarfctxt, fs, int64(0)) // ...plus a 0 offset.
Adduint8(ctxt, fs, dwarf.DW_CFA_same_value) // The platform's link register is unchanged during the prologue.
dwarf.Uleb128put(dwarfctxt, fs, int64(Thearch.Dwarfreglr))
Adduint8(ctxt, fs, dwarf.DW_CFA_val_offset) // The previous value...
dwarf.Uleb128put(dwarfctxt, fs, int64(Thearch.Dwarfregsp)) // ...of the platform's SP register...
dwarf.Uleb128put(dwarfctxt, fs, int64(0)) // ...is CFA+0.
} else {
dwarf.Uleb128put(dwarfctxt, fs, int64(SysArch.PtrSize)) // ...plus the word size (because the call instruction implicitly adds one word to the frame).
Adduint8(ctxt, fs, dwarf.DW_CFA_offset_extended) // The previous value...
dwarf.Uleb128put(dwarfctxt, fs, int64(Thearch.Dwarfreglr)) // ...of the return address...
dwarf.Uleb128put(dwarfctxt, fs, int64(-SysArch.PtrSize)/dataAlignmentFactor) // ...is saved at [CFA - (PtrSize/4)].
}
// 4 is to exclude the length field.
pad := int64(cieReserve) + 4 - fs.Size
if pad < 0 {
Exitf("dwarf: cieReserve too small by %d bytes.", -pad)
}
Addbytes(ctxt, fs, zeros[:pad])
var deltaBuf []byte
var pcsp Pciter
for _, ctxt.Cursym = range ctxt.Textp {
s := ctxt.Cursym
if s.FuncInfo == nil {
continue
}
// Emit a FDE, Section 6.4.1.
// First build the section contents into a byte buffer.
deltaBuf = deltaBuf[:0]
for pciterinit(ctxt, &pcsp, &s.FuncInfo.Pcsp); pcsp.done == 0; pciternext(&pcsp) {
nextpc := pcsp.nextpc
// pciterinit goes up to the end of the function,
// but DWARF expects us to stop just before the end.
if int64(nextpc) == s.Size {
nextpc--
if nextpc < pcsp.pc {
continue
}
}
if haslinkregister(ctxt) {
// TODO(bryanpkc): This is imprecise. In general, the instruction
// that stores the return address to the stack frame is not the
// same one that allocates the frame.
if pcsp.value > 0 {
// The return address is preserved at (CFA-frame_size)
// after a stack frame has been allocated.
deltaBuf = append(deltaBuf, dwarf.DW_CFA_offset_extended_sf)
deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(Thearch.Dwarfreglr))
deltaBuf = dwarf.AppendSleb128(deltaBuf, -int64(pcsp.value)/dataAlignmentFactor)
} else {
// The return address is restored into the link register
// when a stack frame has been de-allocated.
deltaBuf = append(deltaBuf, dwarf.DW_CFA_same_value)
deltaBuf = dwarf.AppendUleb128(deltaBuf, uint64(Thearch.Dwarfreglr))
}
deltaBuf = appendPCDeltaCFA(deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(pcsp.value))
} else {
deltaBuf = appendPCDeltaCFA(deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(SysArch.PtrSize)+int64(pcsp.value))
}
}
pad := int(Rnd(int64(len(deltaBuf)), int64(SysArch.PtrSize))) - len(deltaBuf)
deltaBuf = append(deltaBuf, zeros[:pad]...)
// Emit the FDE header, Section 6.4.1.
// 4 bytes: length, must be multiple of thearch.ptrsize
// 4 bytes: Pointer to the CIE above, at offset 0
// ptrsize: initial location
// ptrsize: address range
Adduint32(ctxt, fs, uint32(4+2*SysArch.PtrSize+len(deltaBuf))) // length (excludes itself)
if Linkmode == LinkExternal {
adddwarfref(ctxt, fs, framesec, 4)
} else {
Adduint32(ctxt, fs, 0) // CIE offset
}
Addaddr(ctxt, fs, s)
adduintxx(ctxt, fs, uint64(s.Size), SysArch.PtrSize) // address range
Addbytes(ctxt, fs, deltaBuf)
}
return syms
}