[PATCH 05/10] objtool: Remove instruction::reloc

From: Peter Zijlstra
Date: Wed Feb 08 2023 - 12:24:27 EST


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, 23448736 mem

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/objtool/check.c | 26 ++++++++++++--------------
tools/objtool/include/objtool/check.h | 6 +++---
2 files changed, 15 insertions(+), 17 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1307,26 +1307,24 @@ __weak bool arch_is_rethunk(struct symbo
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;
-
- insn->reloc = find_reloc_by_dest_range(file->elf, insn->sec,
- insn->offset, insn->len);
- if (!insn->reloc) {
- insn->reloc = NEGATIVE_RELOC;
- return NULL;
- }
+ if (!file)
+ 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)
--- a/tools/objtool/include/objtool/check.h
+++ b/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;