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Date: Fri, 11 Jun 2021 11:19:03 +0200
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Thread-Topic: [dpdk-dev] Define statement with UB prevents compilation using
 UBSAN
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Owen Hilyard" <ohilyard@iol.unh.edu>
Cc: "Aaron Conole" <aconole@redhat.com>,
 "David Marchand" <david.marchand@redhat.com>, "dev" <dev@dpdk.org>,
 "Stephen Hemminger" <stephen@networkplumber.org>
Subject: Re: [dpdk-dev] Define statement with UB prevents compilation using
 UBSAN
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> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen Hemminger
> Sent: Thursday, 10 June 2021 23.36
>=20
> On Thu, 10 Jun 2021 16:51:37 -0400
> Owen Hilyard <ohilyard@iol.unh.edu> wrote:
>=20
> > Working backward to the define
> > statement, AEU_INPUTS_ATTN_BITS_MCP_LATCHED_SCPAD_PARITY is defined
> as
> >
> > #define AEU_INPUTS_ATTN_BITS_MCP_LATCHED_SCPAD_PARITY (0x1 << 31)
>=20
> Why not (1u << 31)?

Yes, this is better. You want the type of the defined constant to be =
uint32_t.

It can also be defined in hexadecimal form as (0x1u << 31), or (0b1u << =
31) in binary form.

<rant>
On the CPUs/compilers supported by DPDK, the exact type of an unsigned =
integer is uint32_t. If the CPU/compiler used 64 bits for integers, you =
would need additional type casting to get it down from 64 to 32 bits.

If we were to be really pedantic, the other defined constants that fit =
in a signed integer, e.g. (1 << 30) should also be defined as (1u << 30) =
if they are supposed to be unsigned integers. However, not many people =
worry about signedness when writing code, especially if an unsigned =
value fits into a signed variable or constant.
</rant>

Thank you for your effort on this, Owen. Keep up the good work! :-)