go/analysis: add frame pointer check for vet

Our calling convention requires BP to be preserved (it is
callee-save).  But that only happened with the introduction of
framepointers in 1.5. Furthermore, nothing checks it, so there is
assembly from before and since which violates the calling
convention. The frame pointer is not used by Go, but only by kernel
traceback code (for sampled profiling), so no one noticed.  Also, the
frame pointer tends to "fix itself", since after it is clobbered by an
assembly function f, the calling function fixes the frame pointer up
when that function returns.

I've fixed the stdlib, CLs 248260, 248261, 248262.

This CL is a simple check, intended to be used in vet, to catch
assembly that violates the calling convention by overwriting the
frame pointer without saving/restoring it. It is not intended to
catch all violations, just ones that are easy to find.

We look for a write to the frame pointer before any use of the frame
pointer or any control flow instruction. In such a situation, there's
no way the code could restore the value of BP before returning. This
analysis is very conservative; it gives up in lots of cases. False
positive should be very rare, though.

Possible false positives:

 // looks like a write to BP, but isn't.

// BP actually isn't clobbered, just swapped with AX.

The first is unlikely, as it is using the contents of an incoming
register, which is junk. The second is a general problem of op=
assembly operations that are indistiguishable in syntax from =
operations.  But anything other than the swap above also depends on
the incoming junk value in BP. The swap itself is pointless (XCHQ
works better).

Change-Id: Ie9d91ab3396409486f7022380ad46ac76c3fbed4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/248686
Trust: Keith Randall <khr@golang.org>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Keith Randall <khr@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
8 files changed
tree: 6b97b93249aa0643a01c30437e0e8da85fcaa684
  1. .gitattributes
  2. .gitignore
  3. .prettierrc
  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/

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.


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.

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