From eacaaed784e2c9da69dea3030c81062c1fd66a37 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Wed, 19 Aug 2020 12:45:18 -0700 Subject: libbpf: Implement enum value-based CO-RE relocations Implement two relocations of a new enumerator value-based CO-RE relocation kind: ENUMVAL_EXISTS and ENUMVAL_VALUE. First, ENUMVAL_EXISTS, allows to detect the presence of a named enumerator value in the target (kernel) BTF. This is useful to do BPF helper/map/program type support detection from BPF program side. bpf_core_enum_value_exists() macro helper is provided to simplify built-in usage. Second, ENUMVAL_VALUE, allows to capture enumerator integer value and relocate it according to the target BTF, if it changes. This is useful to have a guarantee against intentional or accidental re-ordering/re-numbering of some of the internal (non-UAPI) enumerations, where kernel developers don't care about UAPI backwards compatiblity concerns. bpf_core_enum_value() allows to capture this succinctly and use correct enum values in code. LLVM uses ldimm64 instruction to capture enumerator value-based relocations, so add support for ldimm64 instruction patching as well. Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20200819194519.3375898-5-andriin@fb.com --- tools/lib/bpf/bpf_core_read.h | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) (limited to 'tools/lib/bpf/bpf_core_read.h') diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h index 684bfb86361a..bbcefb3ff5a5 100644 --- a/tools/lib/bpf/bpf_core_read.h +++ b/tools/lib/bpf/bpf_core_read.h @@ -31,6 +31,12 @@ enum bpf_type_info_kind { BPF_TYPE_SIZE = 1, /* type size in target kernel */ }; +/* second argument to __builtin_preserve_enum_value() built-in */ +enum bpf_enum_value_kind { + BPF_ENUMVAL_EXISTS = 0, /* enum value existence in kernel */ + BPF_ENUMVAL_VALUE = 1, /* enum value value relocation */ +}; + #define __CORE_RELO(src, field, info) \ __builtin_preserve_field_info((src)->field, BPF_FIELD_##info) @@ -150,6 +156,28 @@ enum bpf_type_info_kind { #define bpf_core_type_size(type) \ __builtin_preserve_type_info(*(typeof(type) *)0, BPF_TYPE_SIZE) +/* + * Convenience macro to check that provided enumerator value is defined in + * a target kernel. + * Returns: + * 1, if specified enum type and its enumerator value are present in target + * kernel's BTF; + * 0, if no matching enum and/or enum value within that enum is found. + */ +#define bpf_core_enum_value_exists(enum_type, enum_value) \ + __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_EXISTS) + +/* + * Convenience macro to get the integer value of an enumerator value in + * a target kernel. + * Returns: + * 64-bit value, if specified enum type and its enumerator value are + * present in target kernel's BTF; + * 0, if no matching enum and/or enum value within that enum is found. + */ +#define bpf_core_enum_value(enum_type, enum_value) \ + __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE) + /* * bpf_core_read() abstracts away bpf_probe_read_kernel() call and captures * offset relocation for source address using __builtin_preserve_access_index() -- cgit v1.2.3