objtool: Remove instruction::reloc

Instead of caching the reloc for each instruction, only keep a
negative cache of not having a reloc (by far the most common case).

 struct instruction {
 	struct list_head           list;                 /*     0    16 */
 	struct hlist_node          hash;                 /*    16    16 */
 	struct list_head           call_node;            /*    32    16 */
 	struct section *           sec;                  /*    48     8 */
 	long unsigned int          offset;               /*    56     8 */
 	/* --- cacheline 1 boundary (64 bytes) --- */
 	long unsigned int          immediate;            /*    64     8 */
 	unsigned int               len;                  /*    72     4 */
 	u8                         type;                 /*    76     1 */

 	/* Bitfield combined with previous fields */

 	u16                        dead_end:1;           /*    76: 8  2 */
 	u16                        ignore:1;             /*    76: 9  2 */
 	u16                        ignore_alts:1;        /*    76:10  2 */
 	u16                        hint:1;               /*    76:11  2 */
 	u16                        save:1;               /*    76:12  2 */
 	u16                        restore:1;            /*    76:13  2 */
 	u16                        retpoline_safe:1;     /*    76:14  2 */
 	u16                        noendbr:1;            /*    76:15  2 */
 	u16                        entry:1;              /*    78: 0  2 */
 	u16                        visited:4;            /*    78: 1  2 */
+	u16                        no_reloc:1;           /*    78: 5  2 */

-	/* XXX 3 bits hole, try to pack */
+	/* XXX 2 bits hole, try to pack */
 	/* Bitfield combined with next fields */

 	s8                         instr;                /*    79     1 */
 	struct alt_group *         alt_group;            /*    80     8 */
 	struct symbol *            call_dest;            /*    88     8 */
 	struct instruction *       jump_dest;            /*    96     8 */
 	struct instruction *       first_jump_src;       /*   104     8 */
 	struct reloc *             jump_table;           /*   112     8 */
-	struct reloc *             reloc;                /*   120     8 */
+	struct alternative *       alts;                 /*   120     8 */
 	/* --- cacheline 2 boundary (128 bytes) --- */
-	struct alternative *       alts;                 /*   128     8 */
-	struct symbol *            sym;                  /*   136     8 */
-	struct stack_op *          stack_ops;            /*   144     8 */
-	struct cfi_state *         cfi;                  /*   152     8 */
+	struct symbol *            sym;                  /*   128     8 */
+	struct stack_op *          stack_ops;            /*   136     8 */
+	struct cfi_state *         cfi;                  /*   144     8 */

-	/* size: 160, cachelines: 3, members: 29 */
-	/* sum members: 158 */
-	/* sum bitfield members: 13 bits, bit holes: 1, sum bit holes: 3 bits */
-	/* last cacheline: 32 bytes */
+	/* size: 152, cachelines: 3, members: 29 */
+	/* sum members: 150 */
+	/* sum bitfield members: 14 bits, bit holes: 1, sum bit holes: 2 bits */
+	/* last cacheline: 24 bytes */
 };

pre:	5:48.89 real,   220.96 user,    127.55 sys,     24834672 mem
post:	5:39.35 real,   215.58 user,    123.69 sys,     2344873 mem

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org> # build only
Tested-by: Thomas Weißschuh <linux@weissschuh.net> # compile and run
Link: https://lore.kernel.org/r/20230208172245.572145269@infradead.org

Author: Peter Zijlstra

tools/objtool/check.c

@@ -1305,26 +1305,24 @@ __weak bool arch_is_rethunk(struct symbol *sym)
 	return false;
 }
 
-#define NEGATIVE_RELOC	((void *)-1L)
-
 static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
 {
-	if (insn->reloc == NEGATIVE_RELOC)
+	struct reloc *reloc;
+
+	if (insn->no_reloc)
 		return NULL;
 
-	if (!insn->reloc) {
-		if (!file)
-			return NULL;
+	if (!file)
+		return NULL;
 
-		insn->reloc = find_reloc_by_dest_range(file->elf, insn->sec,
-						       insn->offset, insn->len);
-		if (!insn->reloc) {
-			insn->reloc = NEGATIVE_RELOC;
-			return NULL;
-		}
+	reloc = find_reloc_by_dest_range(file->elf, insn->sec,
+					 insn->offset, insn->len);
+	if (!reloc) {
+		insn->no_reloc = 1;
+		return NULL;
 	}
 
-	return insn->reloc;
+	return reloc;
 }
 
 static void remove_insn_ops(struct instruction *insn)

tools/objtool/include/objtool/check.h

@@ -55,8 +55,9 @@ struct instruction {
 	   retpoline_safe	: 1,
 	   noendbr		: 1,
 	   entry		: 1,
-	   visited		: 4;
-		/* 3 bit hole */
+	   visited		: 4,
+	   no_reloc		: 1;
+		/* 2 bit hole */
 
 	s8 instr;
 
@@ -65,7 +66,6 @@ struct instruction {
 	struct instruction *jump_dest;
 	struct instruction *first_jump_src;
 	struct reloc *jump_table;
-	struct reloc *reloc;
 	struct alternative *alts;
 	struct symbol *sym;
 	struct stack_op *stack_ops;