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| author | Keith Randall <khr@google.com> | 2018-10-30 13:30:09 -0700 |
|---|---|---|
| committer | Keith Randall <khr@golang.org> | 2018-11-14 21:01:36 +0000 |
| commit | 0c7762cd184649552309c82671bf81f89d215ff7 (patch) | |
| tree | dc33c01dad6596dd41f849a74fdccdea415a7e46 /src/unsafe | |
| parent | a063a2284af69d25d4367ff3e7c6da53f37bad03 (diff) | |
| download | go-0c7762cd184649552309c82671bf81f89d215ff7.tar.gz go-0c7762cd184649552309c82671bf81f89d215ff7.zip | |
cmd/compile: assume unsafe pointer arithmetic generates non-nil results
I've never seen a case where unsafe arithmetic is used to generate a nil.
(Something like var x uintptr; unsafe.Pointer(x - x).)
We can assume that if someone is doing arithmetic with pointers, the
result will be non-nil. Our unsafe rules already forbid this, although
we should be more explicit.
RELNOTE=It is invalid to convert a nil unsafe.Pointer to uintptr and back, with arithmetic.
(This was already invalid, but this statement has been added for clarification.)
Fixes #27180
Change-Id: I1880b7725a9fd99e4613799930fdad9aaa99e8f0
Reviewed-on: https://go-review.googlesource.com/c/146058
Reviewed-by: Austin Clements <austin@google.com>
Diffstat (limited to 'src/unsafe')
| -rw-r--r-- | src/unsafe/unsafe.go | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/src/unsafe/unsafe.go b/src/unsafe/unsafe.go index e16c4aeacb..272761d936 100644 --- a/src/unsafe/unsafe.go +++ b/src/unsafe/unsafe.go @@ -99,6 +99,12 @@ type ArbitraryType int // u := uintptr(p) // p = unsafe.Pointer(u + offset) // +// Note that the pointer must point into an allocated object, so it may not be nil. +// +// // INVALID: conversion of nil pointer +// u := unsafe.Pointer(nil) +// p := unsafe.Pointer(uintptr(u) + offset) +// // (4) Conversion of a Pointer to a uintptr when calling syscall.Syscall. // // The Syscall functions in package syscall pass their uintptr arguments directly |