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Subject[tip: x86/core] objtool: Rework ASM_REACHABLE
The following commit has been merged into the x86/core branch of tip:

Commit-ID: 0d5b64134b49881d62029a1a9923c604507e973b
Gitweb: https://git.kernel.org/tip/0d5b64134b49881d62029a1a9923c604507e973b
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Tue, 08 Mar 2022 16:30:49 +01:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Mar 2022 23:53:37 +01:00

objtool: Rework ASM_REACHABLE

Currently ASM_REACHABLE only works for UD2 instructions; reorder
things to also allow over-riding dead_end_function().

To that end:

- Mark INSN_BUG instructions in decode_instructions(), this saves
having to iterate all instructions yet again.

- Have add_call_destinations() set insn->dead_end for
dead_end_function() calls.

- Move add_dead_ends() *after* add_call_destinations() such that
ASM_REACHABLE can clear the ->dead_end mark.

- have validate_branch() only check ->dead_end.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154319.410010807@infradead.org
---
tools/objtool/check.c | 33 ++++++++++++++++++++-------------
1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9896562..aee6246 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -394,6 +394,14 @@ static int decode_instructions(struct objtool_file *file)
if (ret)
goto err;

+ /*
+ * By default, "ud2" is a dead end unless otherwise
+ * annotated, because GCC 7 inserts it for certain
+ * divide-by-zero cases.
+ */
+ if (insn->type == INSN_BUG)
+ insn->dead_end = true;
+
hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
list_add_tail(&insn->list, &file->insn_list);
nr_insns++;
@@ -523,14 +531,6 @@ static int add_dead_ends(struct objtool_file *file)
struct instruction *insn;

/*
- * By default, "ud2" is a dead end unless otherwise annotated, because
- * GCC 7 inserts it for certain divide-by-zero cases.
- */
- for_each_insn(file, insn)
- if (insn->type == INSN_BUG)
- insn->dead_end = true;
-
- /*
* Check for manually annotated dead ends.
*/
sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
@@ -1113,6 +1113,9 @@ static void annotate_call_site(struct objtool_file *file,
list_add_tail(&insn->call_node, &file->mcount_loc_list);
return;
}
+
+ if (!sibling && dead_end_function(file, sym))
+ insn->dead_end = true;
}

static void add_call_dest(struct objtool_file *file, struct instruction *insn,
@@ -2088,10 +2091,6 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;

- ret = add_dead_ends(file);
- if (ret)
- return ret;
-
add_ignores(file);
add_uaccess_safe(file);

@@ -2130,6 +2129,14 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;

+ /*
+ * Must be after add_call_destinations() such that it can override
+ * dead_end_function() marks.
+ */
+ ret = add_dead_ends(file);
+ if (ret)
+ return ret;
+
ret = add_jump_table_alts(file);
if (ret)
return ret;
@@ -3137,7 +3144,7 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
return 1;
}

- if (dead_end_function(file, insn->call_dest))
+ if (insn->dead_end)
return 0;

break;
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