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Date: Mon, 24 Feb 2025 23:14:59 +0000
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From: "Ihor Solodrai" <ihor.solodrai@linux.dev>
Message-ID: <6b35b7490955800b5cc3833508c88914d59d0d85@linux.dev>
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Subject: Re: [PATCH bpf-next 1/2] libbpf: implement bpf_usdt_arg_size BPF
 function
To: "Andrii Nakryiko" <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org, andrii@kernel.org, ast@kernel.org,
 daniel@iogearbox.net, eddyz87@gmail.com, mykolal@fb.com,
 kernel-team@meta.com
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References: <20250220215904.3362709-1-ihor.solodrai@linux.dev>
 <CAEf4Bzb4T3DcySAyyCXWBK-ShyW9iuE-OM9f7EHXmBJg5Qm0eg@mail.gmail.com>
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On 2/24/25 2:05 PM, Andrii Nakryiko wrote:

> [...]
>
> arg_bitshift is stored as char (which could be signed), so that's why
> you were getting signed division, just cast to unsigned and keep
> division:
>
> return (64 - (unsigned)arg_spec->arg_bitshift) / 8;

As it turns out, this doesn't work either. Presumably because
(64 - (u8)x) is still a signed int.

This works, however:

    return (unsigned char)(64 - arg_spec->arg_bitshift) / 8;

>
>> [...]