| Message ID | 20221103033430.2611623-4-eddyz87@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | libbpf: Resolve unambigous forward declarations | expand |
On Wed, Nov 2, 2022 at 8:35 PM Eduard Zingerman <eddyz87@gmail.com> wrote: > > Resolve forward declarations that don't take part in type graphs > comparisons if declaration name is unambiguous. Example: > > CU #1: > > struct foo; // standalone forward declaration > struct foo *some_global; > > CU #2: > > struct foo { int x; }; > struct foo *another_global; > > The `struct foo` from CU #1 is not a part of any definition that is > compared against another definition while `btf_dedup_struct_types` > processes structural types. The the BTF after `btf_dedup_struct_types` > the BTF looks as follows: > > [1] STRUCT 'foo' size=4 vlen=1 ... > [2] INT 'int' size=4 ... > [3] PTR '(anon)' type_id=1 > [4] FWD 'foo' fwd_kind=struct > [5] PTR '(anon)' type_id=4 > > This commit adds a new pass `btf_dedup_resolve_fwds`, that maps such > forward declarations to structs or unions with identical name in case > if the name is not ambiguous. > > The pass is positioned before `btf_dedup_ref_types` so that types > [3] and [5] could be merged as a same type after [1] and [4] are merged. > The final result for the example above looks as follows: > > [1] STRUCT 'foo' size=4 vlen=1 > 'x' type_id=2 bits_offset=0 > [2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > [3] PTR '(anon)' type_id=1 > > For defconfig kernel with BTF enabled this removes 63 forward > declarations. Examples of removed declarations: `pt_regs`, `in6_addr`. > The running time of `btf__dedup` function is increased by about 3%. > > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> > Reviewed-by: Alan Maguire <alan.maguire@oracle.com> > --- > tools/lib/bpf/btf.c | 143 ++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 139 insertions(+), 4 deletions(-) > LGTM, small nit about hashmap__new initialization Acked-by: Andrii Nakryiko <andrii@kernel.org> > +} > + > +static int btf_dedup_resolve_fwd(struct btf_dedup *d, struct hashmap *names_map, __u32 type_id) > +{ > + struct btf_type *t = btf_type_by_id(d->btf, type_id); > + enum btf_fwd_kind fwd_kind = btf_kflag(t); this is a bit subtle, but probably won't ever break as enum btf_fwd_kind is part of libbpf UAPI > + __u16 cand_kind, kind = btf_kind(t); > + struct btf_type *cand_t; > + uintptr_t cand_id; > + > + if (kind != BTF_KIND_FWD) > + return 0; > + > + /* Skip if this FWD already has a mapping */ > + if (type_id != d->map[type_id]) > + return 0; > + > + if (!hashmap__find(names_map, t->name_off, &cand_id)) > + return 0; > + > + /* Zero is a special value indicating that name is not unique */ > + if (!cand_id) > + return 0; > + > + cand_t = btf_type_by_id(d->btf, cand_id); > + cand_kind = btf_kind(cand_t); > + if ((cand_kind == BTF_KIND_STRUCT && fwd_kind != BTF_FWD_STRUCT) || > + (cand_kind == BTF_KIND_UNION && fwd_kind != BTF_FWD_UNION)) > + return 0; > + > + d->map[type_id] = cand_id; > + > + return 0; > +} > + > +/* > + * Resolve unambiguous forward declarations. > + * > + * The lion's share of all FWD declarations is resolved during > + * `btf_dedup_struct_types` phase when different type graphs are > + * compared against each other. However, if in some compilation unit a > + * FWD declaration is not a part of a type graph compared against > + * another type graph that declaration's canonical type would not be > + * changed. Example: > + * > + * CU #1: > + * > + * struct foo; > + * struct foo *some_global; > + * > + * CU #2: > + * > + * struct foo { int u; }; > + * struct foo *another_global; > + * > + * After `btf_dedup_struct_types` the BTF looks as follows: > + * > + * [1] STRUCT 'foo' size=4 vlen=1 ... > + * [2] INT 'int' size=4 ... > + * [3] PTR '(anon)' type_id=1 > + * [4] FWD 'foo' fwd_kind=struct > + * [5] PTR '(anon)' type_id=4 > + * > + * This pass assumes that such FWD declarations should be mapped to > + * structs or unions with identical name in case if the name is not > + * ambiguous. > + */ > +static int btf_dedup_resolve_fwds(struct btf_dedup *d) > +{ > + int i, err; > + struct hashmap *names_map = > + hashmap__new(btf_dedup_identity_hash_fn, btf_dedup_equal_fn, NULL); if variable declaration and initialization doesn't even fit in a single line, that's a signal that they should better be split. In general we also try to avoid doing "complex" initialization at declaration time. So please split. > + > + if (!names_map) > + return -ENOMEM; > + [...]
On Fri, Nov 4, 2022 at 12:02 PM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Wed, Nov 2, 2022 at 8:35 PM Eduard Zingerman <eddyz87@gmail.com> wrote: > > > > Resolve forward declarations that don't take part in type graphs > > comparisons if declaration name is unambiguous. Example: > > > > CU #1: > > > > struct foo; // standalone forward declaration > > struct foo *some_global; > > > > CU #2: > > > > struct foo { int x; }; > > struct foo *another_global; > > > > The `struct foo` from CU #1 is not a part of any definition that is > > compared against another definition while `btf_dedup_struct_types` > > processes structural types. The the BTF after `btf_dedup_struct_types` > > the BTF looks as follows: > > > > [1] STRUCT 'foo' size=4 vlen=1 ... > > [2] INT 'int' size=4 ... > > [3] PTR '(anon)' type_id=1 > > [4] FWD 'foo' fwd_kind=struct > > [5] PTR '(anon)' type_id=4 > > > > This commit adds a new pass `btf_dedup_resolve_fwds`, that maps such > > forward declarations to structs or unions with identical name in case > > if the name is not ambiguous. > > > > The pass is positioned before `btf_dedup_ref_types` so that types > > [3] and [5] could be merged as a same type after [1] and [4] are merged. > > The final result for the example above looks as follows: > > > > [1] STRUCT 'foo' size=4 vlen=1 > > 'x' type_id=2 bits_offset=0 > > [2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED > > [3] PTR '(anon)' type_id=1 > > > > For defconfig kernel with BTF enabled this removes 63 forward > > declarations. Examples of removed declarations: `pt_regs`, `in6_addr`. > > The running time of `btf__dedup` function is increased by about 3%. > > > > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> > > Reviewed-by: Alan Maguire <alan.maguire@oracle.com> > > --- > > tools/lib/bpf/btf.c | 143 ++++++++++++++++++++++++++++++++++++++++++-- > > 1 file changed, 139 insertions(+), 4 deletions(-) > > > > LGTM, small nit about hashmap__new initialization > > Acked-by: Andrii Nakryiko <andrii@kernel.org> > > > > +} > > + > > +static int btf_dedup_resolve_fwd(struct btf_dedup *d, struct hashmap *names_map, __u32 type_id) > > +{ > > + struct btf_type *t = btf_type_by_id(d->btf, type_id); > > + enum btf_fwd_kind fwd_kind = btf_kflag(t); > > this is a bit subtle, but probably won't ever break as enum > btf_fwd_kind is part of libbpf UAPI > > > + __u16 cand_kind, kind = btf_kind(t); > > + struct btf_type *cand_t; > > + uintptr_t cand_id; > > + > > + if (kind != BTF_KIND_FWD) > > + return 0; > > + > > + /* Skip if this FWD already has a mapping */ > > + if (type_id != d->map[type_id]) > > + return 0; > > + > > + if (!hashmap__find(names_map, t->name_off, &cand_id)) > > + return 0; > > + > > + /* Zero is a special value indicating that name is not unique */ > > + if (!cand_id) > > + return 0; > > + > > + cand_t = btf_type_by_id(d->btf, cand_id); > > + cand_kind = btf_kind(cand_t); > > + if ((cand_kind == BTF_KIND_STRUCT && fwd_kind != BTF_FWD_STRUCT) || > > + (cand_kind == BTF_KIND_UNION && fwd_kind != BTF_FWD_UNION)) > > + return 0; > > + > > + d->map[type_id] = cand_id; > > + > > + return 0; > > +} > > + > > +/* > > + * Resolve unambiguous forward declarations. > > + * > > + * The lion's share of all FWD declarations is resolved during > > + * `btf_dedup_struct_types` phase when different type graphs are > > + * compared against each other. However, if in some compilation unit a > > + * FWD declaration is not a part of a type graph compared against > > + * another type graph that declaration's canonical type would not be > > + * changed. Example: > > + * > > + * CU #1: > > + * > > + * struct foo; > > + * struct foo *some_global; > > + * > > + * CU #2: > > + * > > + * struct foo { int u; }; > > + * struct foo *another_global; > > + * > > + * After `btf_dedup_struct_types` the BTF looks as follows: > > + * > > + * [1] STRUCT 'foo' size=4 vlen=1 ... > > + * [2] INT 'int' size=4 ... > > + * [3] PTR '(anon)' type_id=1 > > + * [4] FWD 'foo' fwd_kind=struct > > + * [5] PTR '(anon)' type_id=4 > > + * > > + * This pass assumes that such FWD declarations should be mapped to > > + * structs or unions with identical name in case if the name is not > > + * ambiguous. > > + */ > > +static int btf_dedup_resolve_fwds(struct btf_dedup *d) > > +{ > > + int i, err; > > + struct hashmap *names_map = > > + hashmap__new(btf_dedup_identity_hash_fn, btf_dedup_equal_fn, NULL); > > if variable declaration and initialization doesn't even fit in a > single line, that's a signal that they should better be split. > > In general we also try to avoid doing "complex" initialization at > declaration time. So please split. > > > + > > + if (!names_map) also: if (IS_ERR(names_map)) return PTR_ERR(names_map); > > + return -ENOMEM; > > + > > [...]
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 04db202aac3d..a847d78efeab 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -2881,6 +2881,7 @@ static int btf_dedup_strings(struct btf_dedup *d); static int btf_dedup_prim_types(struct btf_dedup *d); static int btf_dedup_struct_types(struct btf_dedup *d); static int btf_dedup_ref_types(struct btf_dedup *d); +static int btf_dedup_resolve_fwds(struct btf_dedup *d); static int btf_dedup_compact_types(struct btf_dedup *d); static int btf_dedup_remap_types(struct btf_dedup *d); @@ -2988,15 +2989,16 @@ static int btf_dedup_remap_types(struct btf_dedup *d); * Algorithm summary * ================= * - * Algorithm completes its work in 6 separate passes: + * Algorithm completes its work in 7 separate passes: * * 1. Strings deduplication. * 2. Primitive types deduplication (int, enum, fwd). * 3. Struct/union types deduplication. - * 4. Reference types deduplication (pointers, typedefs, arrays, funcs, func + * 4. Resolve unambiguous forward declarations. + * 5. Reference types deduplication (pointers, typedefs, arrays, funcs, func * protos, and const/volatile/restrict modifiers). - * 5. Types compaction. - * 6. Types remapping. + * 6. Types compaction. + * 7. Types remapping. * * Algorithm determines canonical type descriptor, which is a single * representative type for each truly unique type. This canonical type is the @@ -3060,6 +3062,11 @@ int btf__dedup(struct btf *btf, const struct btf_dedup_opts *opts) pr_debug("btf_dedup_struct_types failed:%d\n", err); goto done; } + err = btf_dedup_resolve_fwds(d); + if (err < 0) { + pr_debug("btf_dedup_resolve_fwds failed:%d\n", err); + goto done; + } err = btf_dedup_ref_types(d); if (err < 0) { pr_debug("btf_dedup_ref_types failed:%d\n", err); @@ -4526,6 +4533,134 @@ static int btf_dedup_ref_types(struct btf_dedup *d) return 0; } +/* + * Collect a map from type names to type ids for all canonical structs + * and unions. If the same name is shared by several canonical types + * use a special value 0 to indicate this fact. + */ +static int btf_dedup_fill_unique_names_map(struct btf_dedup *d, struct hashmap *names_map) +{ + __u32 nr_types = btf__type_cnt(d->btf); + struct btf_type *t; + __u32 type_id; + __u16 kind; + int err; + + /* + * Iterate over base and split module ids in order to get all + * available structs in the map. + */ + for (type_id = 1; type_id < nr_types; ++type_id) { + t = btf_type_by_id(d->btf, type_id); + kind = btf_kind(t); + + if (kind != BTF_KIND_STRUCT && kind != BTF_KIND_UNION) + continue; + + /* Skip non-canonical types */ + if (type_id != d->map[type_id]) + continue; + + err = hashmap__add(names_map, t->name_off, type_id); + if (err == -EEXIST) + err = hashmap__set(names_map, t->name_off, 0, NULL, NULL); + + if (err) + return err; + } + + return 0; +} + +static int btf_dedup_resolve_fwd(struct btf_dedup *d, struct hashmap *names_map, __u32 type_id) +{ + struct btf_type *t = btf_type_by_id(d->btf, type_id); + enum btf_fwd_kind fwd_kind = btf_kflag(t); + __u16 cand_kind, kind = btf_kind(t); + struct btf_type *cand_t; + uintptr_t cand_id; + + if (kind != BTF_KIND_FWD) + return 0; + + /* Skip if this FWD already has a mapping */ + if (type_id != d->map[type_id]) + return 0; + + if (!hashmap__find(names_map, t->name_off, &cand_id)) + return 0; + + /* Zero is a special value indicating that name is not unique */ + if (!cand_id) + return 0; + + cand_t = btf_type_by_id(d->btf, cand_id); + cand_kind = btf_kind(cand_t); + if ((cand_kind == BTF_KIND_STRUCT && fwd_kind != BTF_FWD_STRUCT) || + (cand_kind == BTF_KIND_UNION && fwd_kind != BTF_FWD_UNION)) + return 0; + + d->map[type_id] = cand_id; + + return 0; +} + +/* + * Resolve unambiguous forward declarations. + * + * The lion's share of all FWD declarations is resolved during + * `btf_dedup_struct_types` phase when different type graphs are + * compared against each other. However, if in some compilation unit a + * FWD declaration is not a part of a type graph compared against + * another type graph that declaration's canonical type would not be + * changed. Example: + * + * CU #1: + * + * struct foo; + * struct foo *some_global; + * + * CU #2: + * + * struct foo { int u; }; + * struct foo *another_global; + * + * After `btf_dedup_struct_types` the BTF looks as follows: + * + * [1] STRUCT 'foo' size=4 vlen=1 ... + * [2] INT 'int' size=4 ... + * [3] PTR '(anon)' type_id=1 + * [4] FWD 'foo' fwd_kind=struct + * [5] PTR '(anon)' type_id=4 + * + * This pass assumes that such FWD declarations should be mapped to + * structs or unions with identical name in case if the name is not + * ambiguous. + */ +static int btf_dedup_resolve_fwds(struct btf_dedup *d) +{ + int i, err; + struct hashmap *names_map = + hashmap__new(btf_dedup_identity_hash_fn, btf_dedup_equal_fn, NULL); + + if (!names_map) + return -ENOMEM; + + err = btf_dedup_fill_unique_names_map(d, names_map); + if (err < 0) + goto exit; + + for (i = 0; i < d->btf->nr_types; i++) { + err = btf_dedup_resolve_fwd(d, names_map, d->btf->start_id + i); + if (err < 0) + break; + } + +exit: + hashmap__free(names_map); + return err; +} + /* * Compact types. *
Resolve forward declarations that don't take part in type graphs comparisons if declaration name is unambiguous. Example: CU #1: struct foo; // standalone forward declaration struct foo *some_global; CU #2: struct foo { int x; }; struct foo *another_global; The `struct foo` from CU #1 is not a part of any definition that is compared against another definition while `btf_dedup_struct_types` processes structural types. The the BTF after `btf_dedup_struct_types` the BTF looks as follows: [1] STRUCT 'foo' size=4 vlen=1 ... [2] INT 'int' size=4 ... [3] PTR '(anon)' type_id=1 [4] FWD 'foo' fwd_kind=struct [5] PTR '(anon)' type_id=4 This commit adds a new pass `btf_dedup_resolve_fwds`, that maps such forward declarations to structs or unions with identical name in case if the name is not ambiguous. The pass is positioned before `btf_dedup_ref_types` so that types [3] and [5] could be merged as a same type after [1] and [4] are merged. The final result for the example above looks as follows: [1] STRUCT 'foo' size=4 vlen=1 'x' type_id=2 bits_offset=0 [2] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED [3] PTR '(anon)' type_id=1 For defconfig kernel with BTF enabled this removes 63 forward declarations. Examples of removed declarations: `pt_regs`, `in6_addr`. The running time of `btf__dedup` function is increased by about 3%. Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Reviewed-by: Alan Maguire <alan.maguire@oracle.com> --- tools/lib/bpf/btf.c | 143 ++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 139 insertions(+), 4 deletions(-)