x/tools/go/analysis/passes/unsafeptr: report Header misuse

This CL updates unsafeptr to report about *x and &x expressions where
the pointed-to variable has type reflect.SliceHeader or
reflect.StringHeader.

- Disallowing *x means that reflect.{Slice,String}Header.Data can only
  be accessed using field selection via a *reflect.{Slice,String}Header
  value.

- Disallowing &x means that a *reflect.{Slice,String}Header value can
  only be created by converting from an unsafe.Pointer.

Well, almost only. There are still tricks that can be played to
workaround both of these. For example, a pointer can be dereferenced
via reflection, or a user could write a conversion like:

    type T reflect.SliceHeader
    _ = (*reflect.SliceHeader)(&T{})

But presumably this at least raises the bar enough that someone is
likely to pause to figure out the correct way to use
reflect.{Slice,String}Header.

Notably, disallowing *x and &x does *not* emit warnings for code that
uses reflect.{Slice,String}Header purely as values. For example, the
tests in internal/unsafeheader. Such code is arguably still a
violation of the unsafe.Pointer safety rules ("reflect.SliceHeader and
reflect.StringHeader should be used [...] never as plain structs"),
but is benign.

Updates golang/go#40701.

Change-Id: Id21996bfee07acc0d927a525797dca344bc804d8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/248192
Reviewed-by: Michael Matloob <matloob@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
2 files changed
tree: 316d0acab7c1025410cd7cb9cc6f6b9589247a15
  1. .gitattributes
  2. .gitignore
  3. .prettierrc
  4. AUTHORS
  5. CONTRIBUTING.md
  6. CONTRIBUTORS
  7. LICENSE
  8. PATENTS
  9. README.md
  10. benchmark/
  11. blog/
  12. cmd/
  13. codereview.cfg
  14. container/
  15. cover/
  16. go.mod
  17. go.sum
  18. go/
  19. godoc/
  20. gopls/
  21. imports/
  22. internal/
  23. playground/
  24. present/
  25. refactor/
  26. txtar/
README.md

Go Tools

This subrepository holds the source for various packages and tools that support the Go programming language.

Some of the tools, godoc and vet for example, are included in binary Go distributions.

Others, including the Go guru and the test coverage tool, can be fetched with go get.

Packages include a type-checker for Go and an implementation of the Static Single Assignment form (SSA) representation for Go programs.

Download/Install

The easiest way to install is to run go get -u golang.org/x/tools/.... You can also manually git clone the repository to $GOPATH/src/golang.org/x/tools.

JS/CSS Formatting

This repository uses prettier to format JS and CSS files.

The version of prettier used is 1.18.2.

It is encouraged that all JS and CSS code be run through this before submitting a change. However, it is not a strict requirement enforced by CI.

Report Issues / Send Patches

This repository uses Gerrit for code changes. To learn how to submit changes to this repository, see https://golang.org/doc/contribute.html.

The main issue tracker for the tools repository is located at https://github.com/golang/go/issues. Prefix your issue with “x/tools/(your subdir):” in the subject line, so it is easy to find.