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bpf: Add BTF_ID_LIST/BTF_ID/BTF_ID_UNUSED macros

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Adding support to generate .BTF_ids section that will hold BTF
ID lists for verifier.

Adding macros that will help to define lists of BTF ID values
placed in .BTF_ids section. They are initially filled with zeros
(during compilation) and resolved later during the linking phase
by resolve_btfids tool.

Following defines list of one BTF ID value:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)

It also defines following variable to access the list:

  extern u32 bpf_skb_output_btf_ids[];

The BTF_ID_UNUSED macro defines 4 zero bytes. It's used when we
want to define 'unused' entry in BTF_ID_LIST, like:

  BTF_ID_LIST(bpf_skb_output_btf_ids)
  BTF_ID(struct, sk_buff)
  BTF_ID_UNUSED
  BTF_ID(struct, task_struct)

Suggested-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200711215329.41165-4-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2020-07-11 23:53:23 +02:00 committed by Alexei Starovoitov
parent 33a57ce0a5
commit 5a2798ab32
2 changed files with 91 additions and 0 deletions
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4
include/asm-generic/vmlinux.lds.h
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@ -641,6 +641,10 @@
__start_BTF = .; \
*(.BTF) \
__stop_BTF = .; \
} \
. = ALIGN(4); \
.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) { \
*(.BTF_ids) \
}
#else
#define BTF

87
include/linux/btf_ids.h Normal file
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@ -0,0 +1,87 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_BTF_IDS_H
#define _LINUX_BTF_IDS_H
#include <linux/compiler.h> /* for __PASTE */
/*
* Following macros help to define lists of BTF IDs placed
* in .BTF_ids section. They are initially filled with zeros
* (during compilation) and resolved later during the
* linking phase by resolve_btfids tool.
*
* Any change in list layout must be reflected in resolve_btfids
* tool logic.
*/
#define BTF_IDS_SECTION ".BTF_ids"
#define ____BTF_ID(symbol) \
asm( \
".pushsection " BTF_IDS_SECTION ",\"a\"; \n" \
".local " #symbol " ; \n" \
".type " #symbol ", @object; \n" \
".size " #symbol ", 4; \n" \
#symbol ": \n" \
".zero 4 \n" \
".popsection; \n");
#define __BTF_ID(symbol) \
____BTF_ID(symbol)
#define __ID(prefix) \
__PASTE(prefix, __COUNTER__)
/*
* The BTF_ID defines unique symbol for each ID pointing
* to 4 zero bytes.
*/
#define BTF_ID(prefix, name) \
__BTF_ID(__ID(__BTF_ID__##prefix##__##name##__))
/*
* The BTF_ID_LIST macro defines pure (unsorted) list
* of BTF IDs, with following layout:
*
* BTF_ID_LIST(list1)
* BTF_ID(type1, name1)
* BTF_ID(type2, name2)
*
* list1:
* __BTF_ID__type1__name1__1:
* .zero 4
* __BTF_ID__type2__name2__2:
* .zero 4
*
*/
#define __BTF_ID_LIST(name) \
asm( \
".pushsection " BTF_IDS_SECTION ",\"a\"; \n" \
".local " #name "; \n" \
#name ":; \n" \
".popsection; \n"); \
#define BTF_ID_LIST(name) \
__BTF_ID_LIST(name) \
extern u32 name[];
/*
* The BTF_ID_UNUSED macro defines 4 zero bytes.
* It's used when we want to define 'unused' entry
* in BTF_ID_LIST, like:
*
* BTF_ID_LIST(bpf_skb_output_btf_ids)
* BTF_ID(struct, sk_buff)
* BTF_ID_UNUSED
* BTF_ID(struct, task_struct)
*/
#define BTF_ID_UNUSED \
asm( \
".pushsection " BTF_IDS_SECTION ",\"a\"; \n" \
".zero 4 \n" \
".popsection; \n");
#endif