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runtime: make morestack less subtle

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morestack writes the context pointer to gobuf.ctxt, but since
morestack is written in assembly (and has to be very careful with
state), it does *not* invoke the requisite write barrier for this
write. Instead, we patch this up later, in newstack, where we invoke
an explicit write barrier for ctxt.

This already requires some subtle reasoning, and it's going to get a
lot hairier with the hybrid barrier.

Fix this by simplifying the whole mechanism. Instead of writing
gobuf.ctxt in morestack, just pass the value of the context register
to newstack and let it write it to gobuf.ctxt. This is a normal Go
pointer write, so it gets the normal Go write barrier. No subtle
reasoning required.

Updates #17503.

Change-Id: Ia6bf8459bfefc6828f53682ade32c02412e4db63
Reviewed-on: https://go-review.googlesource.com/31550
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Austin Clements 2016-10-19 18:27:39 -04:00
parent cdccd6a79c
commit bf9c71cb43
9 changed files with 39 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/runtime/asm_386.s
View File

@ -381,7 +381,7 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
MOVL SI, (g_sched+gobuf_g)(SI)
LEAL 4(SP), AX // f's SP
MOVL AX, (g_sched+gobuf_sp)(SI)
MOVL DX, (g_sched+gobuf_ctxt)(SI)
// newstack will fill gobuf.ctxt.
// Call newstack on m->g0's stack.
MOVL m_g0(BX), BP
@ -389,8 +389,10 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
MOVL (g_sched+gobuf_sp)(BP), AX
MOVL -4(AX), BX // fault if CALL would, before smashing SP
MOVL AX, SP
PUSHL DX // ctxt argument
CALL runtime·newstack(SB)
MOVL $0, 0x1003 // crash if newstack returns
POPL DX // keep balance check happy
RET
TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0

4
src/runtime/asm_amd64.s
View File

@ -358,15 +358,17 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
MOVQ SI, (g_sched+gobuf_g)(SI)
LEAQ 8(SP), AX // f's SP
MOVQ AX, (g_sched+gobuf_sp)(SI)
MOVQ DX, (g_sched+gobuf_ctxt)(SI)
MOVQ BP, (g_sched+gobuf_bp)(SI)
// newstack will fill gobuf.ctxt.
// Call newstack on m->g0's stack.
MOVQ m_g0(BX), BX
MOVQ BX, g(CX)
MOVQ (g_sched+gobuf_sp)(BX), SP
PUSHQ DX // ctxt argument
CALL runtime·newstack(SB)
MOVQ $0, 0x1003 // crash if newstack returns
POPQ DX // keep balance check happy
RET
// morestack but not preserving ctxt.

4
src/runtime/asm_amd64p32.s
View File

@ -276,14 +276,16 @@ TEXT runtime·morestack(SB),NOSPLIT,$0-0
MOVL SI, (g_sched+gobuf_g)(SI)
LEAL 8(SP), AX // f's SP
MOVL AX, (g_sched+gobuf_sp)(SI)
MOVL DX, (g_sched+gobuf_ctxt)(SI)
// newstack will fill gobuf.ctxt.
// Call newstack on m->g0's stack.
MOVL m_g0(BX), BX
MOVL BX, g(CX)
MOVL (g_sched+gobuf_sp)(BX), SP
PUSHQ DX // ctxt argument
CALL runtime·newstack(SB)
MOVL $0, 0x1003 // crash if newstack returns
POPQ DX // keep balance check happy
RET
// morestack trampolines

5
src/runtime/asm_arm.s
View File

@ -294,10 +294,10 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0
// Called from f.
// Set g->sched to context in f.
MOVW R7, (g_sched+gobuf_ctxt)(g)
MOVW R13, (g_sched+gobuf_sp)(g)
MOVW LR, (g_sched+gobuf_pc)(g)
MOVW R3, (g_sched+gobuf_lr)(g)
// newstack will fill gobuf.ctxt.
// Called from f.
// Set m->morebuf to f's caller.
@ -310,6 +310,9 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0
MOVW m_g0(R8), R0
BL setg<>(SB)
MOVW (g_sched+gobuf_sp)(g), R13
MOVW $0, R0
MOVW.W R0, -8(R13) // create a call frame on g0
MOVW R7, 4(R13) // ctxt argument
BL runtime·newstack(SB)
// Not reached, but make sure the return PC from the call to newstack

4
src/runtime/asm_arm64.s
View File

@ -269,11 +269,11 @@ TEXT runtime·morestack(SB),NOSPLIT,$-8-0
// Called from f.
// Set g->sched to context in f
MOVD R26, (g_sched+gobuf_ctxt)(g)
MOVD RSP, R0
MOVD R0, (g_sched+gobuf_sp)(g)
MOVD LR, (g_sched+gobuf_pc)(g)
MOVD R3, (g_sched+gobuf_lr)(g)
// newstack will fill gobuf.ctxt.
// Called from f.
// Set m->morebuf to f's callers.
@ -287,6 +287,8 @@ TEXT runtime·morestack(SB),NOSPLIT,$-8-0
BL runtime·save_g(SB)
MOVD (g_sched+gobuf_sp)(g), R0
MOVD R0, RSP
MOVD.W $0, -16(RSP) // create a call frame on g0
MOVD R26, 8(RSP) // ctxt argument
BL runtime·newstack(SB)
// Not reached, but make sure the return PC from the call to newstack

6
src/runtime/asm_mips64x.s
View File

@ -243,10 +243,10 @@ TEXT runtime·morestack(SB),NOSPLIT,$-8-0
// Called from f.
// Set g->sched to context in f.
MOVV REGCTXT, (g_sched+gobuf_ctxt)(g)
MOVV R29, (g_sched+gobuf_sp)(g)
MOVV R31, (g_sched+gobuf_pc)(g)
MOVV R3, (g_sched+gobuf_lr)(g)
// newstack will fill gobuf.ctxt.
// Called from f.
// Set m->morebuf to f's caller.
@ -258,6 +258,10 @@ TEXT runtime·morestack(SB),NOSPLIT,$-8-0
MOVV m_g0(R7), g
JAL runtime·save_g(SB)
MOVV (g_sched+gobuf_sp)(g), R29
// Create a stack frame on g0 to call newstack.
MOVV R0, -16(R29) // Zero saved LR in frame
ADDV $-16, R29
MOVV REGCTXT, 8(R29) // ctxt argument
JAL runtime·newstack(SB)
// Not reached, but make sure the return PC from the call to newstack

4
src/runtime/asm_ppc64x.s
View File

@ -297,11 +297,11 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
// Called from f.
// Set g->sched to context in f.
MOVD R11, (g_sched+gobuf_ctxt)(g)
MOVD R1, (g_sched+gobuf_sp)(g)
MOVD LR, R8
MOVD R8, (g_sched+gobuf_pc)(g)
MOVD R5, (g_sched+gobuf_lr)(g)
// newstack will fill gobuf.ctxt.
// Called from f.
// Set m->morebuf to f's caller.
@ -313,6 +313,8 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
MOVD m_g0(R7), g
BL runtime·save_g(SB)
MOVD (g_sched+gobuf_sp)(g), R1
MOVDU R0, -(FIXED_FRAME+8)(R1) // create a call frame on g0
MOVD R11, FIXED_FRAME+0(R1) // ctxt argument
BL runtime·newstack(SB)
// Not reached, but make sure the return PC from the call to newstack

6
src/runtime/asm_s390x.s
View File

@ -254,11 +254,11 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
// Called from f.
// Set g->sched to context in f.
MOVD R12, (g_sched+gobuf_ctxt)(g)
MOVD R15, (g_sched+gobuf_sp)(g)
MOVD LR, R8
MOVD R8, (g_sched+gobuf_pc)(g)
MOVD R5, (g_sched+gobuf_lr)(g)
// newstack will fill gobuf.ctxt.
// Called from f.
// Set m->morebuf to f's caller.
@ -270,6 +270,10 @@ TEXT runtime·morestack(SB),NOSPLIT|NOFRAME,$0-0
MOVD m_g0(R7), g
BL runtime·save_g(SB)
MOVD (g_sched+gobuf_sp)(g), R15
// Create a stack frame on g0 to call newstack.
MOVD $0, -16(R15) // Zero saved LR in frame
SUB $16, R15
MOVD R12, 8(R15) // ctxt argument
BL runtime·newstack(SB)
// Not reached, but make sure the return PC from the call to newstack

21
src/runtime/stack.go
View File

@ -925,7 +925,10 @@ func round2(x int32) int32 {
//
// g->atomicstatus will be Grunning or Gscanrunning upon entry.
// If the GC is trying to stop this g then it will set preemptscan to true.
func newstack() {
//
// ctxt is the value of the context register on morestack. newstack
// will write it to g.sched.ctxt.
func newstack(ctxt unsafe.Pointer) {
thisg := getg()
// TODO: double check all gp. shouldn't be getg().
if thisg.m.morebuf.g.ptr().stackguard0 == stackFork {
@ -937,8 +940,13 @@ func newstack() {
traceback(morebuf.pc, morebuf.sp, morebuf.lr, morebuf.g.ptr())
throw("runtime: wrong goroutine in newstack")
}
gp := thisg.m.curg
// Write ctxt to gp.sched. We do this here instead of in
// morestack so it has the necessary write barrier.
gp.sched.ctxt = ctxt
if thisg.m.curg.throwsplit {
gp := thisg.m.curg
// Update syscallsp, syscallpc in case traceback uses them.
morebuf := thisg.m.morebuf
gp.syscallsp = morebuf.sp
@ -951,7 +959,6 @@ func newstack() {
throw("runtime: stack split at bad time")
}
gp := thisg.m.curg
morebuf := thisg.m.morebuf
thisg.m.morebuf.pc = 0
thisg.m.morebuf.lr = 0
@ -1003,14 +1010,6 @@ func newstack() {
throw("runtime: split stack overflow")
}
if gp.sched.ctxt != nil {
// morestack wrote sched.ctxt on its way in here,
// without a write barrier. Run the write barrier now.
// It is not possible to be preempted between then
// and now, so it's okay.
writebarrierptr_nostore((*uintptr)(unsafe.Pointer(&gp.sched.ctxt)), uintptr(gp.sched.ctxt))
}
if preempt {
if gp == thisg.m.g0 {
throw("runtime: preempt g0")