[tip: objtool/core] objtool: Rewrite jump_label instructions

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     6d37b83c5d79ef5996cc49c3e3ac3d8ecd8c7050
Gitweb:        https://git.kernel.org/tip/6d37b83c5d79ef5996cc49c3e3ac3d8ecd8c7050
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Thu, 06 May 2021 21:34:03 +02:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 12 May 2021 14:54:56 +02:00

objtool: Rewrite jump_label instructions

When a jump_entry::key has bit1 set, rewrite the instruction to be a
NOP. This allows the compiler/assembler to emit JMP (and thus decide
on which encoding to use).

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210506194158.091028792@xxxxxxxxxxxxx
---
 tools/objtool/check.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9ed1a4c..98cf87f 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1234,6 +1234,20 @@ static int handle_jump_alt(struct objtool_file *file,
 		return -1;
 	}
 
+	if (special_alt->key_addend & 2) {
+		struct reloc *reloc = insn_reloc(file, orig_insn);
+
+		if (reloc) {
+			reloc->type = R_NONE;
+			elf_write_reloc(file->elf, reloc);
+		}
+		elf_write_insn(file->elf, orig_insn->sec,
+			       orig_insn->offset, orig_insn->len,
+			       arch_nop_insn(orig_insn->len));
+		orig_insn->type = INSN_NOP;
+		return 0;
+	}
+
 	*new_insn = list_next_entry(orig_insn, list);
 	return 0;
 }