objtool: Union instruction::{call_dest,jump_table}

The instruction call_dest and jump_table members can never be used at
the same time, their usage depends on type.

 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 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 alternative *       alts;                 /*   120     8 */
+	struct instruction *       jump_dest;            /*    88     8 */
+	struct instruction *       first_jump_src;       /*    96     8 */
+	union {
+		struct symbol *    _call_dest;           /*   104     8 */
+		struct reloc *     _jump_table;          /*   104     8 */
+	};                                               /*   104     8 */
+	struct alternative *       alts;                 /*   112     8 */
+	struct symbol *            sym;                  /*   120     8 */
 	/* --- cacheline 2 boundary (128 bytes) --- */
-	struct symbol *            sym;                  /*   128     8 */
-	struct stack_op *          stack_ops;            /*   136     8 */
-	struct cfi_state *         cfi;                  /*   144     8 */
+	struct stack_op *          stack_ops;            /*   128     8 */
+	struct cfi_state *         cfi;                  /*   136     8 */

-	/* size: 152, cachelines: 3, members: 29 */
-	/* sum members: 150 */
+	/* size: 144, cachelines: 3, members: 28 */
+	/* sum members: 142 */
 	/* sum bitfield members: 14 bits, bit holes: 1, sum bit holes: 2 bits */
-	/* last cacheline: 24 bytes */
+	/* last cacheline: 16 bytes */
 };

pre:	5:39.35 real,   215.58 user,    123.69 sys,     23448736 mem
post:	5:38.18 real,   213.25 user,    124.90 sys,     23449040 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/20230208172245.640914454@infradead.org

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index fffc8b86f9f3..ab6deaed9777 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -62,10 +62,12 @@ struct instruction {
 	s8 instr;
 
 	struct alt_group *alt_group;
-	struct symbol *call_dest;
 	struct instruction *jump_dest;
 	struct instruction *first_jump_src;
-	struct reloc *jump_table;
+	union {
+		struct symbol *_call_dest;
+		struct reloc *_jump_table;
+	};
 	struct alternative *alts;
 	struct symbol *sym;
 	struct stack_op *stack_ops;