tools/resolve_btfids: Refactor set sorting with types from btf_ids.h

Instead of using magic offsets to access BTF ID set data, leverage types
from btf_ids.h (btf_id_set and btf_id_set8) which define the actual
layout of the data. Thanks to this change, set sorting should also
continue working if the layout changes.

This requires to sync the definition of 'struct btf_id_set8' from
include/linux/btf_ids.h to tools/include/linux/btf_ids.h. We don't sync
the rest of the file at the moment, b/c that would require to also sync
multiple dependent headers and we don't need any other defs from
btf_ids.h.

Signed-off-by: Viktor Malik <vmalik@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Daniel Xu <dxu@dxuuu.xyz>
Link: https://lore.kernel.org/bpf/ff7f062ddf6a00815fda3087957c4ce667f50532.1707223196.git.vmalik@redhat.com

tools/bpf/resolve_btfids/main.c

@@ -70,6 +70,7 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <errno.h>
+#include <linux/btf_ids.h>
 #include <linux/rbtree.h>
 #include <linux/zalloc.h>
 #include <linux/err.h>
@@ -78,7 +79,7 @@
 #include <subcmd/parse-options.h>
 
 #define BTF_IDS_SECTION	".BTF_ids"
-#define BTF_ID		"__BTF_ID__"
+#define BTF_ID_PREFIX	"__BTF_ID__"
 
 #define BTF_STRUCT	"struct"
 #define BTF_UNION	"union"
@@ -161,7 +162,7 @@ static int eprintf(int level, int var, const char *fmt, ...)
 
 static bool is_btf_id(const char *name)
 {
-	return name && !strncmp(name, BTF_ID, sizeof(BTF_ID) - 1);
+	return name && !strncmp(name, BTF_ID_PREFIX, sizeof(BTF_ID_PREFIX) - 1);
 }
 
 static struct btf_id *btf_id__find(struct rb_root *root, const char *name)
@@ -441,7 +442,7 @@ static int symbols_collect(struct object *obj)
 		 * __BTF_ID__TYPE__vfs_truncate__0
 		 * prefix =  ^
 		 */
-		prefix = name + sizeof(BTF_ID) - 1;
+		prefix = name + sizeof(BTF_ID_PREFIX) - 1;
 
 		/* struct */
 		if (!strncmp(prefix, BTF_STRUCT, sizeof(BTF_STRUCT) - 1)) {
@@ -649,19 +650,18 @@ static int cmp_id(const void *pa, const void *pb)
 static int sets_patch(struct object *obj)
 {
 	Elf_Data *data = obj->efile.idlist;
-	int *ptr = data->d_buf;
 	struct rb_node *next;
 
 	next = rb_first(&obj->sets);
 	while (next) {
-		unsigned long addr, idx;
+		struct btf_id_set8 *set8;
+		struct btf_id_set *set;
+		unsigned long addr, off;
 		struct btf_id *id;
-		int *base;
-		int cnt;
 
 		id   = rb_entry(next, struct btf_id, rb_node);
 		addr = id->addr[0];
-		idx  = addr - obj->efile.idlist_addr;
+		off = addr - obj->efile.idlist_addr;
 
 		/* sets are unique */
 		if (id->addr_cnt != 1) {
@@ -670,14 +670,21 @@ static int sets_patch(struct object *obj)
 			return -1;
 		}
 
-		idx = idx / sizeof(int);
-		base = &ptr[idx] + (id->is_set8 ? 2 : 1);
-		cnt = ptr[idx];
+		if (id->is_set) {
+			set = data->d_buf + off;
+			qsort(set->ids, set->cnt, sizeof(set->ids[0]), cmp_id);
+		} else {
+			set8 = data->d_buf + off;
+			/*
+			 * Make sure id is at the beginning of the pairs
+			 * struct, otherwise the below qsort would not work.
+			 */
+			BUILD_BUG_ON(set8->pairs != &set8->pairs[0].id);
+			qsort(set8->pairs, set8->cnt, sizeof(set8->pairs[0]), cmp_id);
+		}
 
 		pr_debug("sorting  addr %5lu: cnt %6d [%s]\n",
-			 (idx + 1) * sizeof(int), cnt, id->name);
-
-		qsort(base, cnt, id->is_set8 ? sizeof(uint64_t) : sizeof(int), cmp_id);
+			 off, id->is_set ? set->cnt : set8->cnt, id->name);
 
 		next = rb_next(next);
 	}

tools/include/linux/btf_ids.h

@@ -8,6 +8,15 @@ struct btf_id_set {
 	u32 ids[];
 };
 
+struct btf_id_set8 {
+	u32 cnt;
+	u32 flags;
+	struct {
+		u32 id;
+		u32 flags;
+	} pairs[];
+};
+
 #ifdef CONFIG_DEBUG_INFO_BTF
 
 #include <linux/compiler.h> /* for __PASTE */