From 00d01b57866d4b052c3b75706bbc8601167ead7c Mon Sep 17 00:00:00 2001
From: Cherry Mui <cherryyz@google.com>
Date: Fri, 4 Jun 2021 17:18:09 -0400
Subject: [PATCH] [dev.typeparams] runtime: remove tracebackdefers

tracebackdefers is used for scanning/copying deferred functions'
arguments. Now that deferred functions are always argumentless,
it does nothing. Remove.

Change-Id: I55bedabe5584ea41a12cdb03d55ec9692a5aacd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/325916
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
---
 src/runtime/mgcmark.go   |  7 ++-----
 src/runtime/stack.go     |  5 -----
 src/runtime/traceback.go | 32 --------------------------------
 3 files changed, 2 insertions(+), 42 deletions(-)

diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 1fd0732d62..eb70ae9f49 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -750,14 +750,11 @@ func scanstack(gp *g, gcw *gcWork) {
 	// Find additional pointers that point into the stack from the heap.
 	// Currently this includes defers and panics. See also function copystack.
 
-	// Find and trace all defer arguments.
-	tracebackdefers(gp, scanframe, nil)
-
 	// Find and trace other pointers in defer records.
 	for d := gp._defer; d != nil; d = d.link {
 		if d.fn != nil {
-			// tracebackdefers above does not scan the func value, which could
-			// be a stack allocated closure. See issue 30453.
+			// Scan the func value, which could be a stack allocated closure.
+			// See issue 30453.
 			scanblock(uintptr(unsafe.Pointer(&d.fn)), sys.PtrSize, &oneptrmask[0], gcw, &state)
 		}
 		if d.link != nil {
diff --git a/src/runtime/stack.go b/src/runtime/stack.go
index a1182b00bd..b5545ac796 100644
--- a/src/runtime/stack.go
+++ b/src/runtime/stack.go
@@ -753,11 +753,6 @@ func adjustdefers(gp *g, adjinfo *adjustinfo) {
 		adjustpointer(adjinfo, unsafe.Pointer(&d.varp))
 		adjustpointer(adjinfo, unsafe.Pointer(&d.fd))
 	}
-
-	// Adjust defer argument blocks the same way we adjust active stack frames.
-	// Note: this code is after the loop above, so that if a defer record is
-	// stack allocated, we work on the copy in the new stack.
-	tracebackdefers(gp, adjustframe, noescape(unsafe.Pointer(adjinfo)))
 }
 
 func adjustpanics(gp *g, adjinfo *adjustinfo) {
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index 2564273a53..3fc9d07fc5 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -21,38 +21,6 @@ import (
 
 const usesLR = sys.MinFrameSize > 0
 
-// Traceback over the deferred function calls.
-// Report them like calls that have been invoked but not started executing yet.
-func tracebackdefers(gp *g, callback func(*stkframe, unsafe.Pointer) bool, v unsafe.Pointer) {
-	var frame stkframe
-	for d := gp._defer; d != nil; d = d.link {
-		fn := d.fn
-		if fn == nil {
-			// Defer of nil function. Args don't matter.
-			frame.pc = 0
-			frame.fn = funcInfo{}
-			frame.argp = 0
-			frame.arglen = 0
-			frame.argmap = nil
-		} else {
-			frame.pc = fn.fn
-			f := findfunc(frame.pc)
-			if !f.valid() {
-				print("runtime: unknown pc in defer ", hex(frame.pc), "\n")
-				throw("unknown pc")
-			}
-			frame.fn = f
-			frame.argp = 0
-			frame.arglen = 0
-			frame.argmap = nil
-		}
-		frame.continpc = frame.pc
-		if !callback((*stkframe)(noescape(unsafe.Pointer(&frame))), v) {
-			return
-		}
-	}
-}
-
 const sizeofSkipFunction = 256
 
 // Generic traceback. Handles runtime stack prints (pcbuf == nil),