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 int bpf_skb_output_btf_ids[];
Suggested-by: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
include/asm-generic/vmlinux.lds.h | 4 ++
include/linux/btf_ids.h | 69 +++++++++++++++++++++++++++++++
2 files changed, 73 insertions(+)
create mode 100644 include/linux/btf_ids.h
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index db600ef218d7..a9b77a4314a8 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -641,6 +641,10 @@
__start_BTF = .; \
*(.BTF) \
__stop_BTF = .; \
+ } \
+ . = ALIGN(4); \
+ .BTF.ids : AT(ADDR(.BTF.ids) - LOAD_OFFSET) { \
+ *(.BTF.ids) \
}
#else
#define BTF
diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
new file mode 100644
index 000000000000..f7f9dc4d9a9f
--- /dev/null
+++ b/include/linux/btf_ids.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_BTF_IDS_H
+#define _LINUX_BTF_IDS_H 1
+
+#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 btfid tool.
+ *
+ * Any change in list layout must be reflected in btfid
+ * 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 int name[];
+
+#endif
--
2.25.4
