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runtime, cmd/internal/obj: get rid of rewindmorestack

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In the function prologue, we emit a jump to the beginning of
the function immediately after calling morestack. And in the
runtime stack growing code, it decodes and emulates that jump.
This emulation was necessary before we had per-PC SP deltas,
since the traceback code assumed that the frame size was fixed
for the whole function, except on the first instruction where
it was 0. Since we now have per-PC SP deltas and PCDATA, we
can correctly record that the frame size is 0. This makes the
emulation unnecessary.

This may be helpful for registerized calling convention, where
there may be unspills of arguments after calling morestack. It
also simplifies the runtime.

Change-Id: I7ebee31eaee81795445b33f521ab6a79624c4ceb
Reviewed-on: https://go-review.googlesource.com/30138
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Cherry Zhang 2016-10-02 17:10:13 -04:00
parent 56b746974c
commit 4c9a372946
13 changed files with 103 additions and 147 deletions
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14
src/cmd/internal/obj/arm/obj5.go
View file

@ -803,12 +803,24 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
for last = ctxt.Cursym.Text; last.Link != nil; last = last.Link {
}
// Now we are at the end of the function, but logically
// we are still in function prologue. We need to fix the
// SP data and PCDATA.
spfix := obj.Appendp(ctxt, last)
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := obj.Appendp(ctxt, spfix)
pcdata.Lineno = ctxt.Cursym.Text.Lineno
pcdata.Mode = ctxt.Cursym.Text.Mode
pcdata.As = obj.APCDATA
pcdata.From.Type = obj.TYPE_CONST
pcdata.From.Offset = obj.PCDATA_StackMapIndex
pcdata.To.Type = obj.TYPE_CONST
pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
// MOVW LR, R3
movw := obj.Appendp(ctxt, spfix)
movw := obj.Appendp(ctxt, pcdata)
movw.As = AMOVW
movw.From.Type = obj.TYPE_REG
movw.From.Reg = REGLINK

14
src/cmd/internal/obj/arm64/obj7.go
View file

@ -161,12 +161,24 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
for last = ctxt.Cursym.Text; last.Link != nil; last = last.Link {
}
// Now we are at the end of the function, but logically
// we are still in function prologue. We need to fix the
// SP data and PCDATA.
spfix := obj.Appendp(ctxt, last)
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := obj.Appendp(ctxt, spfix)
pcdata.Lineno = ctxt.Cursym.Text.Lineno
pcdata.Mode = ctxt.Cursym.Text.Mode
pcdata.As = obj.APCDATA
pcdata.From.Type = obj.TYPE_CONST
pcdata.From.Offset = obj.PCDATA_StackMapIndex
pcdata.To.Type = obj.TYPE_CONST
pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
// MOV LR, R3
movlr := obj.Appendp(ctxt, spfix)
movlr := obj.Appendp(ctxt, pcdata)
movlr.As = AMOVD
movlr.From.Type = obj.TYPE_REG
movlr.From.Reg = REGLINK

17
src/cmd/internal/obj/pcln.go
View file

@ -25,11 +25,12 @@ func addvarint(ctxt *Link, d *Pcdata, val uint32) {
// where func is the function, val is the current value, p is the instruction being
// considered, and arg can be used to further parameterize valfunc.
func funcpctab(ctxt *Link, dst *Pcdata, func_ *LSym, desc string, valfunc func(*Link, *LSym, int32, *Prog, int32, interface{}) int32, arg interface{}) {
// To debug a specific function, uncomment second line and change name.
// To debug a specific function, uncomment lines and change name.
dbg := 0
//dbg = strcmp(func->name, "main.main") == 0;
//dbg = strcmp(desc, "pctofile") == 0;
//if func_.Name == "main.main" || desc == "pctospadj" {
// dbg = 1
//}
ctxt.Debugpcln += int32(dbg)
@ -214,9 +215,15 @@ func linkpcln(ctxt *Link, cursym *LSym) {
npcdata := 0
nfuncdata := 0
for p := cursym.Text; p != nil; p = p.Link {
if p.As == APCDATA && p.From.Offset >= int64(npcdata) {
// Find the highest ID of any used PCDATA table. This ignores PCDATA table
// that consist entirely of "-1", since that's the assumed default value.
// From.Offset is table ID
// To.Offset is data
if p.As == APCDATA && p.From.Offset >= int64(npcdata) && p.To.Offset != -1 { // ignore -1 as we start at -1, if we only see -1, nothing changed
npcdata = int(p.From.Offset + 1)
}
// Find the highest ID of any FUNCDATA table.
// From.Offset is table ID
if p.As == AFUNCDATA && p.From.Offset >= int64(nfuncdata) {
nfuncdata = int(p.From.Offset + 1)
}
@ -243,7 +250,7 @@ func linkpcln(ctxt *Link, cursym *LSym) {
havefunc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
}
if p.As == APCDATA {
if p.As == APCDATA && p.To.Offset != -1 {
havepc[p.From.Offset/32] |= 1 << uint64(p.From.Offset%32)
}
}

35
src/cmd/internal/obj/ppc64/obj9.go
View file

@ -823,6 +823,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
}
*/
func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
p0 := p // save entry point, but skipping the two instructions setting R2 in shared mode
// MOVD g_stackguard(g), R3
p = obj.Appendp(ctxt, p)
@ -953,6 +955,24 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
morestacksym = obj.Linklookup(ctxt, "runtime.morestack", 0)
}
if ctxt.Flag_shared {
// In PPC64 PIC code, R2 is used as TOC pointer derived from R12
// which is the address of function entry point when entering
// the function. We need to preserve R2 across call to morestack.
// Fortunately, in shared mode, 8(SP) and 16(SP) are reserved in
// the caller's frame, but not used (0(SP) is caller's saved LR,
// 24(SP) is caller's saved R2). Use 8(SP) to save this function's R2.
// MOVD R12, 8(SP)
p = obj.Appendp(ctxt, p)
p.As = AMOVD
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R2
p.To.Type = obj.TYPE_MEM
p.To.Reg = REGSP
p.To.Offset = 8
}
if ctxt.Flag_dynlink {
// Avoid calling morestack via a PLT when dynamically linking. The
// PLT stubs generated by the system linker on ppc64le when "std r2,
@ -1000,12 +1020,23 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
p.To.Type = obj.TYPE_BRANCH
p.To.Sym = morestacksym
}
if ctxt.Flag_shared {
// MOVD 8(SP), R2
p = obj.Appendp(ctxt, p)
p.As = AMOVD
p.From.Type = obj.TYPE_MEM
p.From.Reg = REGSP
p.From.Offset = 8
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R2
}
// BR start
p = obj.Appendp(ctxt, p)
p.As = ABR
p.To.Type = obj.TYPE_BRANCH
p.Pcond = ctxt.Cursym.Text.Link
p.Pcond = p0.Link
// placeholder for q1's jump target
p = obj.Appendp(ctxt, p)

21
src/cmd/internal/obj/s390x/objz.go
View file

@ -599,7 +599,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
}
}
if wasSplit {
pLast = stacksplitPost(ctxt, pLast, pPre, pPreempt) // emit post part of split check
pLast = stacksplitPost(ctxt, pLast, pPre, pPreempt, autosize) // emit post part of split check
}
}
@ -775,10 +775,25 @@ func stacksplitPre(ctxt *obj.Link, p *obj.Prog, framesize int32) (*obj.Prog, *ob
return p, q
}
func stacksplitPost(ctxt *obj.Link, p *obj.Prog, pPre *obj.Prog, pPreempt *obj.Prog) *obj.Prog {
func stacksplitPost(ctxt *obj.Link, p *obj.Prog, pPre *obj.Prog, pPreempt *obj.Prog, framesize int32) *obj.Prog {
// Now we are at the end of the function, but logically
// we are still in function prologue. We need to fix the
// SP data and PCDATA.
spfix := obj.Appendp(ctxt, p)
spfix.As = obj.ANOP
spfix.Spadj = -framesize
pcdata := obj.Appendp(ctxt, spfix)
pcdata.Lineno = ctxt.Cursym.Text.Lineno
pcdata.Mode = ctxt.Cursym.Text.Mode
pcdata.As = obj.APCDATA
pcdata.From.Type = obj.TYPE_CONST
pcdata.From.Offset = obj.PCDATA_StackMapIndex
pcdata.To.Type = obj.TYPE_CONST
pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
// MOVD LR, R5
p = obj.Appendp(ctxt, p)
p = obj.Appendp(ctxt, pcdata)
pPre.Pcond = p
p.As = AMOVD
p.From.Type = obj.TYPE_REG

14
src/cmd/internal/obj/x86/obj6.go
View file

@ -1113,11 +1113,23 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32, textarg int32) *ob
for last = ctxt.Cursym.Text; last.Link != nil; last = last.Link {
}
// Now we are at the end of the function, but logically
// we are still in function prologue. We need to fix the
// SP data and PCDATA.
spfix := obj.Appendp(ctxt, last)
spfix.As = obj.ANOP
spfix.Spadj = -framesize
call := obj.Appendp(ctxt, spfix)
pcdata := obj.Appendp(ctxt, spfix)
pcdata.Lineno = ctxt.Cursym.Text.Lineno
pcdata.Mode = ctxt.Cursym.Text.Mode
pcdata.As = obj.APCDATA
pcdata.From.Type = obj.TYPE_CONST
pcdata.From.Offset = obj.PCDATA_StackMapIndex
pcdata.To.Type = obj.TYPE_CONST
pcdata.To.Offset = -1 // pcdata starts at -1 at function entry
call := obj.Appendp(ctxt, pcdata)
call.Lineno = ctxt.Cursym.Text.Lineno
call.Mode = ctxt.Cursym.Text.Mode
call.As = obj.ACALL

3
src/runtime/stack.go
View file

@ -602,7 +602,7 @@ func adjustpointers(scanp unsafe.Pointer, cbv *bitvector, adjinfo *adjustinfo, f
}
if minp <= p && p < maxp {
if stackDebug >= 3 {
print("adjust ptr ", p, " ", funcname(f), "\n")
print("adjust ptr ", hex(p), " ", funcname(f), "\n")
}
if useCAS {
ppu := (*unsafe.Pointer)(unsafe.Pointer(pp))
@ -957,7 +957,6 @@ func newstack() {
thisg.m.morebuf.lr = 0
thisg.m.morebuf.sp = 0
thisg.m.morebuf.g = 0
rewindmorestack(&gp.sched)
// NOTE: stackguard0 may change underfoot, if another thread
// is about to try to preempt gp. Read it just once and use that same

17
src/runtime/sys_arm.go
View file

@ -17,22 +17,5 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint32
if buf.pc&3 == 0 && buf.pc != 0 {
inst = *(*uint32)(unsafe.Pointer(buf.pc))
if inst>>24 == 0x9a || inst>>24 == 0xea {
buf.pc += uintptr(int32(inst<<8)>>6) + 8
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}
// for testing
func usplit(x uint32) (q, r uint32)

18
src/runtime/sys_arm64.go
View file

@ -16,21 +16,3 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.pc = uintptr(fn)
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint32
if buf.pc&3 == 0 && buf.pc != 0 {
inst = *(*uint32)(unsafe.Pointer(buf.pc))
// section C3.2.6 Unconditional branch (immediate)
if inst>>26 == 0x05 {
buf.pc += uintptr(int32(inst<<6) >> 4)
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}

23
src/runtime/sys_mips64x.go
View file

@ -18,26 +18,3 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.pc = uintptr(fn)
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint32
if buf.pc&3 == 0 && buf.pc != 0 {
inst = *(*uint32)(unsafe.Pointer(buf.pc))
if inst>>26 == 2 { // JMP addr
//print("runtime: rewind pc=", hex(buf.pc), " to pc=", hex(buf.pc &^ uintptr(1<<28-1) | uintptr((inst&^0xfc000000)<<2)), "\n");
buf.pc &^= 1<<28 - 1
buf.pc |= uintptr((inst &^ 0xfc000000) << 2)
return
}
if inst>>16 == 0x1000 { // BEQ R0, R0, offset
//print("runtime: rewind pc=", hex(buf.pc), " to pc=", hex(buf.pc + uintptr(int32(int16(inst&0xffff))<<2 + 4)), "\n");
buf.pc += uintptr(int32(int16(inst&0xffff))<<2 + 4)
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}

17
src/runtime/sys_ppc64x.go
View file

@ -19,21 +19,4 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint32
if buf.pc&3 == 0 && buf.pc != 0 {
inst = *(*uint32)(unsafe.Pointer(buf.pc))
if inst>>26 == 18 && inst&3 == 0 {
//print("runtime: rewind pc=", hex(buf.pc), " to pc=", hex(uintptr(buf.pc + int32(inst<<6)>>6)), "\n");
buf.pc += uintptr(int32(inst<<6) >> 6)
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}
func prepGoExitFrame(sp uintptr)

27
src/runtime/sys_s390x.go
View file

@ -16,30 +16,3 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.pc = uintptr(fn)
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
var inst uint64
if buf.pc&1 == 0 && buf.pc != 0 {
inst = *(*uint64)(unsafe.Pointer(buf.pc))
switch inst >> 48 {
case 0xa7f4: // BRC (branch relative on condition) instruction.
inst >>= 32
inst &= 0xFFFF
offset := int64(int16(inst))
offset <<= 1
buf.pc += uintptr(offset)
return
case 0xc0f4: // BRCL (branch relative on condition long) instruction.
inst >>= 16
inst = inst & 0xFFFFFFFF
inst = (inst << 1) & 0xFFFFFFFF
buf.pc += uintptr(int32(inst))
return
}
}
print("runtime: pc=", hex(buf.pc), " ", hex(inst), "\n")
throw("runtime: misuse of rewindmorestack")
}

30
src/runtime/sys_x86.go
View file

@ -25,33 +25,3 @@ func gostartcall(buf *gobuf, fn, ctxt unsafe.Pointer) {
buf.pc = uintptr(fn)
buf.ctxt = ctxt
}
// Called to rewind context saved during morestack back to beginning of function.
// To help us, the linker emits a jmp back to the beginning right after the
// call to morestack. We just have to decode and apply that jump.
func rewindmorestack(buf *gobuf) {
pc := (*[8]byte)(unsafe.Pointer(buf.pc))
if pc[0] == 0xe9 { // jmp 4-byte offset
buf.pc = buf.pc + 5 + uintptr(int64(*(*int32)(unsafe.Pointer(&pc[1]))))
return
}
if pc[0] == 0xeb { // jmp 1-byte offset
buf.pc = buf.pc + 2 + uintptr(int64(*(*int8)(unsafe.Pointer(&pc[1]))))
return
}
if pc[0] == 0xcc {
// This is a breakpoint inserted by gdb. We could use
// runtime·findfunc to find the function. But if we
// do that, then we will continue execution at the
// function entry point, and we will not hit the gdb
// breakpoint. So for this case we don't change
// buf.pc, so that when we return we will execute
// the jump instruction and carry on. This means that
// stack unwinding may not work entirely correctly
// (https://golang.org/issue/5723) but the user is
// running under gdb anyhow.
return
}
print("runtime: pc=", pc, " ", hex(pc[0]), " ", hex(pc[1]), " ", hex(pc[2]), " ", hex(pc[3]), " ", hex(pc[4]), "\n")
throw("runtime: misuse of rewindmorestack")
}