Potential undefined behavior when using reinterpret_cast #30300
Description
Steps to reproduce
Compile this project.
Standard C++ (Working Draft):
3.65[defns.undefined]undefined behavior
behavior for which this document imposes no requirements
[Note 1: Undefined behavior may be expected when this document omits any explicit definition of behavior or when a program uses an incorrect construct or invalid data. Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message ([defns.diagnostic])), to terminating a translation or execution (with the issuance of a diagnostic message). Many incorrect program constructs do not engender undefined behavior; they are required to be diagnosed. Evaluation of a constant expression ([expr.const]) never exhibits behavior explicitly specified as undefined in [intro] through [cpp]. — end note]
3.50[defns.undefined.runtime]runtime-undefined behavior
behavior that is undefined except when it occurs during constant evaluation
[Note 1: During constant evaluation,
it is implementation-defined whether runtime-undefined behavior results in the expression being deemed non-constant (as specified in [expr.const]) and
runtime-undefined behavior has no other effect.
— end note]
Expected behaviour
Correct program without UB.
Actual behaviour
Standard C++ (Working Draft):
3.65[defns.undefined]undefined behavior
behavior for which this document imposes no requirements
[Note 1: Undefined behavior may be expected when this document omits any explicit definition of behavior or when a program uses an incorrect construct or invalid data. Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message ([defns.diagnostic])), to terminating a translation or execution (with the issuance of a diagnostic message). Many incorrect program constructs do not engender undefined behavior; they are required to be diagnosed. Evaluation of a constant expression ([expr.const]) never exhibits behavior explicitly specified as undefined in [intro] through [cpp]. — end note]
3.50[defns.undefined.runtime]runtime-undefined behavior
behavior that is undefined except when it occurs during constant evaluation
[Note 1: During constant evaluation,
it is implementation-defined whether runtime-undefined behavior results in the expression being deemed non-constant (as specified in [expr.const]) and
runtime-undefined behavior has no other effect.
— end note]
This lines use
reinterpret_cast from string (?) to uint32, uint64, uint16. Here a program attempts to access the stored value of an object through a glvalue through which it is not type-accessible.
But:
https://eel.is/c++draft/basic.lval#11
11 An object of dynamic type Tobj is type-accessible through a glvalue of type Tref if Tref is similar ([conv.qual]) to:
(11.1) -- Tobj,
(11.2) -- a type that is the signed or unsigned type corresponding to Tobj, or
(11.3) -- a char, unsigned char, or std::byte type.If a program attempts to access ([defns.access]) the stored value of an object through a glvalue through which it is not type-accessible, the behavior is undefined.38
https://eel.is/c++draft/basic.compound#5
5
#
Two objects a and b are pointer-interconvertible if
(5.1) -- they are the same object, or
(5.2) -- one is a union object and the other is a non-static data member of that object ([class.union]), or
(5.3) -- one is a standard-layout class object and the other is the first non-static data member of that object or any base class subobject of that object ([class.mem]), or
(5.4) -- there exists an object c such that a and c are pointer-interconvertible, and c and b are pointer-interconvertible.If two objects are pointer-interconvertible, then they have the same address, and it is possible to obtain a pointer to one from a pointer to the other via a reinterpret_cast ([expr.reinterpret.cast]).
fix: #30301
Operating system
linux
Version of Telegram Desktop
dev
Installation source
Static binary from official website
Crash ID
No response