tools headers: Adopt verbatim copy of btf_ids.h from kernel sources

It will be needed by bpf selftest for resolve_btfids tool.

Also adding __PASTE macro as btf_ids.h dependency, which is
defined in:

  include/linux/compiler_types.h

but because tools/include do not have this header, I'm putting
the macro into linux/compiler.h header.

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/20200711215329.41165-9-jolsa@kernel.org

tools/include/linux/btf_ids.h

@@ -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

tools/include/linux/compiler.h

@@ -201,4 +201,8 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 # define __fallthrough
 #endif
 
+/* Indirect macros required for expanded argument pasting, eg. __LINE__. */
+#define ___PASTE(a, b) a##b
+#define __PASTE(a, b) ___PASTE(a, b)
+
 #endif /* _TOOLS_LINUX_COMPILER_H */