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Date: Wed, 10 Jan 2024 15:44:30 -0800
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Subject: Re: [RFC bpf-next] bpf, selftests/bpf: Support PTR_MAYBE_NULL for
 struct_ops arguments.
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To: thinker.li@gmail.com
Cc: sinquersw@gmail.com, kuifeng@meta.com, bpf@vger.kernel.org,
 ast@kernel.org, song@kernel.org, kernel-team@meta.com, andrii@kernel.org,
 davemarchevsky@meta.com, dvernet@meta.com
References: <20240110221750.798813-1-thinker.li@gmail.com>
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From: Martin KaFai Lau <martin.lau@linux.dev>
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On 1/10/24 2:17 PM, thinker.li@gmail.com wrote:
> The proposed solution here is to add PTR_MAYBE_NULL annotations to
> arguments

[ ... ]

> == Future Work ==
> 
> We require an improved method for annotating arguments. Initially, we
> anticipated annotating arguments by appending a suffix to argument names,
> such as arg1__maybe_null. However, this approach does not function for
> function pointers due to compiler limitations. Nevertheless, it does work
> for functions. To resolve this, we need compiler support to enable the
> inclusion of argument names in the DWARF for function pointer types.

After reading the high level of the patch,
while it needs compiler work to support decl tagging (or arg name) in a 
struct_ops's func_proto, changing the info->reg_type of a struct_ops's argument 
have been doable in the ".is_valid_access" without new kernel code change in 
verifier/btf.c.

Take a look at the bpf_tcp_ca_is_valid_access() which promotes the info->btf_id 
to "struct tcp_sock". The same could be done for info->reg_type (e.g. adding 
PTR_MAYBE_NULL).