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borkmannborkmann
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Merge branch 'bpf-btf-type-fixes'
Yonghong Song says: ==================== Commit 69b693f ("bpf: btf: Introduce BPF Type Format (BTF)") introduced BTF, a debug info format for BTF. The original design has a couple of issues though. First, the bitfield size is only encoded in int type. If the struct member bitfield type is enum, pahole ([1]) or llvm is forced to replace enum with int type. As a result, the original type information gets lost. Second, the original BTF design does not envision the possibility of BTF=>header_file conversion ([2]), hence does not encode "struct" or "union" info for a forward type. Such information is necessary to convert BTF to a header file. This patch set fixed the issue by introducing kind_flag, using one bit in type->info. When kind_flag, the struct/union btf_member->offset will encode both bitfield_size and bit_offset, covering both int and enum base types. The kind_flag is also used to indicate whether the forward type is a union (when set) or a struct. Patch #1 refactors function btf_int_bits_seq_show() so Patch #2 can reuse part of the function. Patch #2 implemented kind_flag support for struct/union/fwd types. Patch #3 added kind_flag support for cgroup local storage map pretty print. Patch #4 syncs kernel uapi btf.h to tools directory. Patch #5 added unit tests for kind_flag. Patch torvalds#6 added tests for kernel bpffs based pretty print with kind_flag. Patch torvalds#7 refactors function btf_dumper_int_bits() so Patch torvalds#8 can reuse part of the function. Patch torvalds#8 added bpftool support of pretty print with kind_flag set. [1] https://git.kernel.org/pub/scm/devel/pahole/pahole.git/commit/?id=b18354f64cc215368c3bc0df4a7e5341c55c378c [2] https://lwn.net/SubscriberLink/773198/fe3074838f5c3f26/ Change logs: v2 -> v3: . Relocated comments about bitfield_size/bit_offset interpretation of the "offset" field right before the "offset" struct member. . Added missing byte alignment checking for non-bitfield enum member of a struct with kind_flag set. . Added two test cases in unit tests for struct type, kind_flag set, non-bitfield int/enum member, not-byte aligned bit offsets. . Added comments to help understand there is no overflow for total_bits_offset in bpftool function btf_dumper_int_bits(). . Added explanation of typedef type dumping fix in Patch torvalds#8 commit message. v1 -> v2: . If kind_flag is set for a structure, ensure an int member, whether it is a bitfield or not, is a regular int type. . Added support so cgroup local storage map pretty print works with kind_flag. ==================== Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
2 parents 6c4fc20 + 8772c8b commit 37c7b1c

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‎include/linux/btf.h

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@
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#include <linux/types.h>
88

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struct btf;
10+
struct btf_member;
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struct btf_type;
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union bpf_attr;
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@@ -46,7 +47,9 @@ void btf_type_seq_show(const struct btf *btf, u32 type_id, void *obj,
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struct seq_file *m);
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int btf_get_fd_by_id(u32 id);
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u32 btf_id(const struct btf *btf);
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bool btf_type_is_reg_int(const struct btf_type *t, u32 expected_size);
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bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
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const struct btf_member *m,
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u32 expected_offset, u32 expected_size);
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#ifdef CONFIG_BPF_SYSCALL
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const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);

‎include/uapi/linux/btf.h

Lines changed: 18 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -34,7 +34,9 @@ struct btf_type {
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* bits 0-15: vlen (e.g. # of struct's members)
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* bits 16-23: unused
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* bits 24-27: kind (e.g. int, ptr, array...etc)
37-
* bits 28-31: unused
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* bits 28-30: unused
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* bit 31: kind_flag, currently used by
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* struct, union and fwd
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*/
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__u32 info;
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/* "size" is used by INT, ENUM, STRUCT and UNION.
@@ -52,6 +54,7 @@ struct btf_type {
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#define BTF_INFO_KIND(info) (((info) >> 24) & 0x0f)
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#define BTF_INFO_VLEN(info) ((info) & 0xffff)
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#define BTF_INFO_KFLAG(info) ((info) >> 31)
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#define BTF_KIND_UNKN 0 /* Unknown */
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#define BTF_KIND_INT 1 /* Integer */
@@ -110,9 +113,22 @@ struct btf_array {
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struct btf_member {
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__u32 name_off;
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__u32 type;
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__u32 offset; /* offset in bits */
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/* If the type info kind_flag is set, the btf_member offset
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* contains both member bitfield size and bit offset. The
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* bitfield size is set for bitfield members. If the type
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* info kind_flag is not set, the offset contains only bit
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* offset.
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*/
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__u32 offset;
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};
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/* If the struct/union type info kind_flag is set, the
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* following two macros are used to access bitfield_size
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* and bit_offset from btf_member.offset.
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*/
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#define BTF_MEMBER_BITFIELD_SIZE(val) ((val) >> 24)
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#define BTF_MEMBER_BIT_OFFSET(val) ((val) & 0xffffff)
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/* BTF_KIND_FUNC_PROTO is followed by multiple "struct btf_param".
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* The exact number of btf_param is stored in the vlen (of the
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* info in "struct btf_type").

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