runtime: do not attempt bulkBarrierPreWrite when dst slice length is zero

If dst slice length is zero in makeslicecopy then the called mallocgc is
using a fast path to only return a pointer to runtime.zerobase.
There may be no heapBits for that address readable by
bulkBarrierPreWriteSrcOnly which will cause a panic.

Protect against this by not calling bulkBarrierPreWriteSrcOnly if
there is nothing to copy. This is the case for all cases where the
length of the destination slice is zero.

runtime.growslice and runtime.typedslicecopy have fast paths that
do not call bulkBarrierPreWrite for zero copy lengths either.

Fixes #38929

Change-Id: I78ece600203a0a8d24de5b6c9eef56f605d44e99
Reviewed-on: https://go-review.googlesource.com/c/go/+/232800
Reviewed-by: Keith Randall <khr@golang.org>
1 file changed
tree: 0e4a6766d00c07a5f98c6d5979c0ddb1c5727d09
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. AUTHORS
  11. CONTRIBUTING.md
  12. CONTRIBUTORS
  13. favicon.ico
  14. LICENSE
  15. PATENTS
  16. README.md
  17. robots.txt
  18. SECURITY.md
README.md

The Go Programming Language

Go is an open source programming language that makes it easy to build simple, reliable, and efficient software.

Gopher image Gopher image by Renee French, licensed under Creative Commons 3.0 Attributions license.

Our canonical Git repository is located at https://go.googlesource.com/go. There is a mirror of the repository at https://github.com/golang/go.

Unless otherwise noted, the Go source files are distributed under the BSD-style license found in the LICENSE file.

Download and Install

Binary Distributions

Official binary distributions are available at https://golang.org/dl/.

After downloading a binary release, visit https://golang.org/doc/install or load doc/install.html in your web browser for installation instructions.

Install From Source

If a binary distribution is not available for your combination of operating system and architecture, visit https://golang.org/doc/install/source or load doc/install-source.html in your web browser for source installation instructions.

Contributing

Go is the work of thousands of contributors. We appreciate your help!

To contribute, please read the contribution guidelines: https://golang.org/doc/contribute.html

Note that the Go project uses the issue tracker for bug reports and proposals only. See https://golang.org/wiki/Questions for a list of places to ask questions about the Go language.