runtime: assume precisestack, copystack, StackCopyAlways, ScanStackByFrames

Commit to stack copying for stack growth.

We're carrying around a surprising amount of cruft from older schemes.
I am confident that precise stack scans and stack copying are here to stay.

Delete fallback code for when precise stack info is disabled.
Delete fallback code for when copying stacks is disabled.
Delete fallback code for when StackCopyAlways is disabled.
Delete Stktop chain - there is only one stack segment now.
Delete M.moreargp, M.moreargsize, M.moreframesize, M.cret.
Delete G.writenbuf (unrelated, just dead).
Delete runtime.lessstack, runtime.oldstack.
Delete many amd64 morestack variants.
Delete initialization of morestack frame/arg sizes (shortens split prologue!).

Replace G's stackguard/stackbase/stack0/stacksize/
syscallstack/syscallguard/forkstackguard with simple stack
bounds (lo, hi).

Update liblink, runtime/cgo for adjustments to G.

LGTM=khr
R=khr, bradfitz
CC=golang-codereviews, iant, r
https://codereview.appspot.com/137410043

1 files changed, 8 insertions, 31 deletions

diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index af536f079..ac78bd9dc 100644
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -31,9 +31,11 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$-4
 
 	// create istack out of the OS stack
 	MOVW	$(-8192+104)(R13), R0
-	MOVW	R0, g_stackguard(g)	// (w 104b guard)
 	MOVW	R0, g_stackguard0(g)
-	MOVW	R13, g_stackbase(g)
+	MOVW	R0, g_stackguard1(g)
+	MOVW	R0, (g_stack+stack_lo)(g)
+	MOVW	R13, (g_stack+stack_hi)(g)
+
 	BL	runtime·emptyfunc(SB)	// fault if stack check is wrong
 
 #ifndef GOOS_nacl
@@ -51,8 +53,10 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$-4
 
 nocgo:
 	// update stackguard after _cgo_init
-	MOVW	g_stackguard0(g), R0
-	MOVW	R0, g_stackguard(g)
+	MOVW	(g_stack+stack_lo)(g), R0
+	ADD	$const_StackGuard, R0
+	MOVW	R0, g_stackguard0(g)
+	MOVW	R0, g_stackguard1(g)
 
 	BL	runtime·checkgoarm(SB)
 	BL	runtime·check(SB)
@@ -287,9 +291,6 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0
 	CMP	g, R4
 	BL.EQ	runtime·abort(SB)
 
-	MOVW	R1, m_moreframesize(R8)
-	MOVW	R2, m_moreargsize(R8)
-
 	// Called from f.
 	// Set g->sched to context in f.
 	MOVW	R7, (g_sched+gobuf_ctxt)(g)
@@ -302,7 +303,6 @@ TEXT runtime·morestack(SB),NOSPLIT,$-4-0
 	MOVW	R3, (m_morebuf+gobuf_pc)(R8)	// f's caller's PC
 	MOVW	SP, (m_morebuf+gobuf_sp)(R8)	// f's caller's SP
 	MOVW	$4(SP), R3			// f's argument pointer
-	MOVW	R3, m_moreargp(R8)	
 	MOVW	g, (m_morebuf+gobuf_g)(R8)
 
 	// Call newstack on m->g0's stack.
@@ -436,22 +436,6 @@ CALLFN(runtime·call268435456, 268435456)
 CALLFN(runtime·call536870912, 536870912)
 CALLFN(runtime·call1073741824, 1073741824)
 
-// Return point when leaving stack.
-// using frame size $-4 means do not save LR on stack.
-//
-// Lessstack can appear in stack traces for the same reason
-// as morestack; in that context, it has 0 arguments.
-TEXT runtime·lessstack(SB),NOSPLIT,$-4-0
-	// Save return value in m->cret
-	MOVW	g_m(g), R8
-	MOVW	R0, m_cret(R8)
-
-	// Call oldstack on m->g0's stack.
-	MOVW	m_g0(R8), R0
-	BL	setg<>(SB)
-	MOVW	(g_sched+gobuf_sp)(g), SP
-	BL	runtime·oldstack(SB)
-
 // void jmpdefer(fn, sp);
 // called from deferreturn.
 // 1. grab stored LR for caller
@@ -721,13 +705,6 @@ TEXT runtime·atomicloaduintptr(SB),NOSPLIT,$0-8
 TEXT runtime·atomicloaduint(SB),NOSPLIT,$0-8
 	B	runtime·atomicload(SB)
 
-TEXT runtime·stackguard(SB),NOSPLIT,$0-8
-	MOVW	R13, R1
-	MOVW	g_stackguard(g), R2
-	MOVW	R1, sp+0(FP)
-	MOVW	R2, limit+4(FP)
-	RET
-
 // AES hashing not implemented for ARM
 TEXT runtime·aeshash(SB),NOSPLIT,$-4-0
 	MOVW	$0, R0