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This patch introduces the "__uptr" type tag to BTF. It is to define a pointer pointing to the user space memory. This patch adds BTF logic to pass the "__uptr" type tag. btf_find_kptr() is reused for the "__uptr" tag. The "__uptr" will only be supported in the map_value of the task storage map. However, btf_parse_struct_meta() also uses btf_find_kptr() but it is not interested in "__uptr". This patch adds a "field_mask" argument to btf_find_kptr() which will return BTF_FIELD_IGNORE if the caller is not interested in a “__uptr” field. btf_parse_kptr() is also reused to parse the uptr. The btf_check_and_fixup_fields() is changed to do extra checks on the uptr to ensure that its struct size is not larger than PAGE_SIZE. It is not clear how a uptr pointing to a CO-RE supported kernel struct will be used, so it is also not allowed now. Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org> Link: https://lore.kernel.org/r/20241023234759.860539-2-martin.lau@linux.dev Signed-off-by: Alexei Starovoitov <ast@kernel.org>