linux-kernel - Re: [PATCH v2 bpf 07/11] samples/bpf: fix uin64

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Date:   Thu, 21 Apr 2022 22:55:08 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Alexander Lobakin <alobakin@...me>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Song Liu <songliubraving@...com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 bpf 07/11] samples/bpf: fix uin64_t format literals

From: David Laight <David.Laight@...LAB.COM>
Date: Thu, 21 Apr 2022 07:46:05 +0000

> From: Alexander Lobakin
> > Sent: 21 April 2022 01:40
> >
> > There's a couple places where uin64_t is being passed as an %lu
> > format argument. That type is defined as unsigned long on 64-bit
> > systems and as unsigned long long on 32-bit, so neither %lu nor
> > %llu are not universal.
> > One of the options is %PRIu64, but since it's always 8-byte long,
> > just cast it to the _proper_ __u64 and print as %llu.
>
> Is __u64 guaranteed to be 'unsigned long long' ? No reason why it should be.
> I think you need to cast to (unsigned long long).

__u64 can be unsigned long only if an architecture uses int-l64.h
instead of int-ll64.h. This is currently possible for Alpha and
PPC64 when __SANE_USERSPACE_TYPES__ is not defined -- I guess you
know what that flag does.
I messed up a bit and didn't notice that samples/bpf/Makefile
defines this flag only for MIPS. IMO it should be defined in here
unconditionally, but I guess it's out of bpf-fixes scope, so I'll
go with unsigned long long in v3 (got to resend with no PGP crap
anyway lol).

>
> 	David

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Thanks,
Al