runtime, reflect: access runtime.reflectcall directly

Currently, package runtime contains the definition of reflect.call,
even though it's just a jump to runtime.reflectcall. This "push"
symbol is confusing, since it's not clear where the definition of
reflect.call comes from when you're in the reflect package.

Replace this with a "pull" symbol: the runtime now defines only
runtime.reflectcall and package reflect uses a go:linkname to access
this symbol directly. This makes it clear where reflect.call is coming
from without any spooky action at a distance and eliminates all of the
definitions of reflect.call in the runtime.

Change-Id: I3ec73cd394efe9df8d3061a57c73aece2e7048dd
Reviewed-on: https://go-review.googlesource.com/c/148657
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/vet/all/whitelist/all.txt

@@ -10,7 +10,6 @@ go/types/scope.go: method WriteTo(w io.Writer, n int, recurse bool) should have
 // False positives.
 
 // Nothing much to do about cross-package assembly. Unfortunate.
-runtime/asm_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly function: call is in package reflect
 internal/bytealg/equal_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly function: memequal is in package runtime
 internal/bytealg/equal_ARCHSUFF.s: [GOARCH] cannot check cross-package assembly function: memequal_varlen is in package runtime
 

src/reflect/value.go

@@ -2667,6 +2667,8 @@ func maplen(m unsafe.Pointer) int
 // back into arg+retoffset before returning. If copying result bytes back,
 // the caller must pass the argument frame type as argtype, so that
 // call can execute appropriate write barriers during the copy.
+//
+//go:linkname call runtime.reflectcall
 func call(argtype *rtype, fn, arg unsafe.Pointer, n uint32, retoffset uint32)
 
 func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)

src/runtime/asm_386.s

@@ -493,9 +493,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	JMP	AX
 // Note: can't just "JMP NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	JMP	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT, $0-20
 	MOVL	argsize+12(FP), CX
 	DISPATCH(runtime·call16, 16)

src/runtime/asm_amd64.s

@@ -448,9 +448,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0
 	JMP	AX
 // Note: can't just "JMP NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	JMP	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT, $0-32
 	MOVLQZX argsize+24(FP), CX
 	DISPATCH(runtime·call32, 32)

src/runtime/asm_amd64p32.s

@@ -318,9 +318,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0
 	JMP	AX
 // Note: can't just "JMP NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	JMP	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT, $0-20
 	MOVLQZX argsize+12(FP), CX
 	DISPATCH(runtime·call16, 16)

src/runtime/asm_arm.s

@@ -439,9 +439,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	MOVW	$NAME(SB), R1;		\
 	B	(R1)
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	B	·reflectcall(SB)
-
 TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
 	MOVW	argsize+12(FP), R0
 	DISPATCH(runtime·call16, 16)

src/runtime/asm_arm64.s

@@ -330,9 +330,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	B	(R27)
 // Note: can't just "B NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	B	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	MOVWU argsize+24(FP), R16
 	DISPATCH(runtime·call32, 32)

src/runtime/asm_mips64x.s

@@ -292,9 +292,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	JMP	(R4)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	JMP	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	MOVWU argsize+24(FP), R1
 	DISPATCH(runtime·call32, 32)

src/runtime/asm_mipsx.s

@@ -291,9 +291,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT,$0-0
 	MOVW	$NAME(SB), R4;	\
 	JMP	(R4)
 
-TEXT reflect·call(SB),NOSPLIT,$0-20
-	JMP	·reflectcall(SB)
-
 TEXT ·reflectcall(SB),NOSPLIT|NOFRAME,$0-20
 	MOVW	argsize+12(FP), R1
 

src/runtime/asm_ppc64x.s

@@ -355,9 +355,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	(CTR)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	BR	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT|NOFRAME, $0-32
 	MOVWZ argsize+24(FP), R3
 	DISPATCH(runtime·call32, 32)

src/runtime/asm_s390x.s

@@ -381,9 +381,6 @@ TEXT runtime·morestack_noctxt(SB),NOSPLIT|NOFRAME,$0-0
 	BR	(R5)
 // Note: can't just "BR NAME(SB)" - bad inlining results.
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	BR	·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT, $-8-32
 	MOVWZ argsize+24(FP), R3
 	DISPATCH(runtime·call32, 32)

src/runtime/asm_wasm.s

@@ -293,9 +293,6 @@ TEXT ·cgocallback_gofunc(SB), NOSPLIT, $16-32
 		JMP NAME(SB); \
 	End
 
-TEXT reflect·call(SB), NOSPLIT, $0-0
-	JMP ·reflectcall(SB)
-
 TEXT ·reflectcall(SB), NOSPLIT, $0-32
 	I64Load fn+8(FP)
 	I64Eqz

src/runtime/stubs.go

@@ -154,6 +154,8 @@ func breakpoint()
 // one call that copies results back, in cgocallbackg1, and it does NOT pass a
 // frame type, meaning there are no write barriers invoked. See that call
 // site for justification.
+//
+// Package reflect accesses this symbol through a linkname.
 func reflectcall(argtype *_type, fn, arg unsafe.Pointer, argsize uint32, retoffset uint32)
 
 func procyield(cycles uint32)