x/tools/go/analysis/passes/unsafeptr: verify that unsafe pointer arithmetic happens within one expression

[DanielMorsing]

From the unsafe.Pointer docs:

Note that both conversions must appear in the same expression, with only the intervening arithmetic between them:

// INVALID: uintptr cannot be stored in variable
// before conversion back to Pointer.
u := uintptr(p)
p = unsafe.Pointer(u + offset)

I have definitely seen (and written) this idiom before in the runtime code (although a specific example eludes me at the moment). We should verify this in the unsafeptr analysis pass

[thepudds]

FWIW, I believe checktpr (like -gcflags=all=-d=checkptr or -gcflags=all=-d=checkptr=2) is pretty good at catching that at execution time, and I think vet does complain about at least basic cases:

https://go.dev/play/p/uS33btV84UN

	u := uintptr(p)
	p = unsafe.Pointer(u + offset) // vet: ./prog.go:16:6: possible misuse of unsafe.Pointer

I think checkptr does not instrument the runtime, though. Not sure whether that vet check skips the runtime.

(And sorry if I misunderstood.)

[DanielMorsing]

It does indeed. I tried this with gopls, but it didn't catch my test file because of a workspace issue

[gabyhelp]

Related Issues

• x/tools/go/analysis/passes/modernize: replace unsafe pointer arithmetic with unsafe.Add(ptr, n) #76648

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