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define (un)sound and UB #190

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Merged
merged 6 commits into from
Aug 27, 2019
Merged

define (un)sound and UB #190

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160e361
define (un)sound
RalfJung Aug 5, 2019
e8860ce
less awkward
RalfJung Aug 5, 2019
f7a0a3a
use soundness in explaining the safety invariant
RalfJung Aug 6, 2019
849d3bf
define UB and give some context to soundness
RalfJung Aug 6, 2019
7c04179
Full stop
RalfJung Aug 7, 2019
53aec0b
compiler and unsafe code authors share this burden
RalfJung Aug 15, 2019
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5 changes: 5 additions & 0 deletions reference/src/glossary.md
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Expand Up @@ -146,6 +146,11 @@ Moreover, such unsafe code must not return a non-UTF-8 string to the "outside" o
To summarize: *Data must always be valid, but it only must be safe in safe code.*
For some more information, see [this blog post](https://www.ralfj.de/blog/2018/08/22/two-kinds-of-invariants.html).

#### Soundness (of code / of a library)

We say that a library (can be an individual function) is *sound* if it is impossible for safe code to cause Undefined Behavior using its public API.
Conversely, the library is *unsound* if safe code *can* cause Undefined Behavior.

#### Layout

The *layout* of a type defines its size and alignment as well as the offsets of its subobjects (e.g. fields of structs/unions/enum/... or elements of arrays).
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