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([2600:1700:6cf8:1240:a9ce:8a39:867c:8f30]) by smtp.gmail.com with ESMTPSA id r187-20020a0de8c4000000b0060a304ca3f4sm1601526ywe.19.2024.03.12.17.37.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Mar 2024 17:37:41 -0700 (PDT) Message-ID: Date: Tue, 12 Mar 2024 17:37:40 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH bpf-next] bpftool: cast pointers for shadow types explicitly. Content-Language: en-US To: Andrii Nakryiko Cc: Kui-Feng Lee , bpf@vger.kernel.org, ast@kernel.org, martin.lau@linux.dev, song@kernel.org, kernel-team@meta.com, andrii@kernel.org, kuifeng@meta.com, yhs@meta.com References: <20240312013726.1780720-1-thinker.li@gmail.com> From: Kui-Feng Lee In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 3/12/24 17:27, Andrii Nakryiko wrote: > On Tue, Mar 12, 2024 at 5:08 PM Kui-Feng Lee wrote: >> >> >> >> On 3/12/24 15:47, Andrii Nakryiko wrote: >>> On Mon, Mar 11, 2024 at 6:38 PM Kui-Feng Lee wrote: >>>> >>>> According to a report, skeletons fail to assign shadow pointers when being >>>> compiled with C++ programs. Unlike C doing implicit casting for void >>>> pointers, C++ requires an explicit casting. >>>> >>>> To support C++, we do explicit casting for each shadow pointer. >>>> >>>> Cc: yhs@meta.com >>>> Signed-off-by: Kui-Feng Lee >>>> --- >>>> tools/bpf/bpftool/gen.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c >>>> index 4fa4ade1ce74..dedafea0c127 100644 >>>> --- a/tools/bpf/bpftool/gen.c >>>> +++ b/tools/bpf/bpftool/gen.c >>>> @@ -1131,7 +1131,7 @@ static void gen_st_ops_shadow_init(struct btf *btf, struct bpf_object *obj) >>>> continue; >>>> codegen("\ >>>> \n\ >>>> - obj->struct_ops.%1$s = bpf_map__initial_value(obj->maps.%1$s, NULL);\n\ >>>> + obj->struct_ops.%1$s = (typeof(obj->struct_ops.%1$s))bpf_map__initial_value(obj->maps.%1$s, NULL);\n\ >>> >>> Given we have a named struct type for this and we use explicit type >>> names in other parts of generated skeleton code, let's maybe use >>> "struct %s__%s__%s" explicitly here (passing in obj_name, ident, >>> type_name)? >> >> I have considered about this solution. But, C++ works differently. It >> has nested namespaces. That means it should be referred as >> "XXX_skeleton::OOO_st_ops_map" in C++. Then, we need #if #else #endif >> directives to provide two separated casting. >> > > we cast to (struct *) by name of the skeleton, so it should > be fine, I don't see why we'd need to do something C++ specific here The skeleton looks like struct struct_ops_module { ...... struct { struct struct_ops_module__testmod_zeroed__bpf_testmod_ops___zeroed { .... } testmod_zeroed; } struct_ops; }; struct struct_ops_module__testmod_zeroed__bpf_testmod_ops___zeroed is inside of struct struct_ops_module. In C++, it should be referred as "struct_ops_module::struct_ops_module__testmod_zeroed__bpf_testmod_ops___zeroed". The other option is moving definitions of these types to the top scope. > >>> >>> No strong preferences, but feels like a consistent approach here would be nice. >>> >>>> \n\ >>>> ", ident); >>>> } >>>> -- >>>> 2.34.1 >>>>