From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [DPDK/core Bug 1506] Fix undefined behavior in RTE_IPV4 macro
Date: Tue, 30 Jul 2024 08:11:09 +0000 [thread overview]
Message-ID: <bug-1506-3@http.bugs.dpdk.org/> (raw)
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https://bugs.dpdk.org/show_bug.cgi?id=1506
Bug ID: 1506
Summary: Fix undefined behavior in RTE_IPV4 macro
Product: DPDK
Version: 24.07
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: core
Assignee: dev@dpdk.org
Reporter: user202729@protonmail.com
Target Milestone: ---
Currently we have the following definition
```
/** Create IPv4 address */
#define RTE_IPV4(a, b, c, d) ((uint32_t)(((a) & 0xff) << 24) | \
(((b) & 0xff) << 16) | \
(((c) & 0xff) << 8) | \
((d) & 0xff))
```
The problem is that the cast to `uint32_t` is done after the shift, and
overflowing left shift is undefined behavior in C and C++:
https://stackoverflow.com/questions/3784996/why-does-left-shift-operation-invoke-undefined-behaviour-when-the-left-side-oper
.
The fix is easy, just cast the `(a) & 0xff` to `uint32_t` before shifting it by
24.
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