From: Cherry Zhang <cherryyz@google.com>
Date: Wed, 18 Nov 2020 00:10:51 +0000 (-0500)
Subject: [release-branch.go1.15] cmd/link: recompute heapPos after copyHeap
X-Git-Tag: go1.15.6~1
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=480da601431545e3415e25515ac342c583935599;p=gostls13.git

[release-branch.go1.15] cmd/link: recompute heapPos after copyHeap

Immediately after a forward Seek, the offset we're writing to is
beyond len(buf)+len(heap):

|<--- buf --->|<--- heap --->|
                                    ^
                                    off

If we do a copyHeap at this point, the new heapPos should not be
0:

|<---------- buf ----------->|<-heap->|
                                    ^
                                    off

Recompute it.

Updates #42082
Fixes #42948

Change-Id: Icb3e4e1c7bf7d1fd3d76a2e0d7dfcb319c661534
Reviewed-on: https://go-review.googlesource.com/c/go/+/270942
Run-TryBot: Carlos Amedee <carlos@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Trust: Cherry Zhang <cherryyz@google.com>
---

diff --git a/src/cmd/link/internal/ld/outbuf.go b/src/cmd/link/internal/ld/outbuf.go
index 09162ae90f..7bc89540c6 100644
--- a/src/cmd/link/internal/ld/outbuf.go
+++ b/src/cmd/link/internal/ld/outbuf.go
@@ -187,7 +187,9 @@ func (out *OutBuf) writeLoc(lenToWrite int64) (int64, []byte) {
 		// See if our heap would grow to be too large, and if so, copy it to the end
 		// of the mmapped area.
 		if heapLen > maxOutBufHeapLen && out.copyHeap() {
-			heapPos, heapLen, lenNeeded = 0, 0, lenToWrite
+			heapPos -= heapLen
+			lenNeeded = heapPos + lenToWrite
+			heapLen = 0
 		}
 		out.heap = append(out.heap, make([]byte, lenNeeded-heapLen)...)
 	}