lkml.org 
[lkml]   [2018]   [Jan]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/4] objtool: Add support for alternatives at the end of a section
Date
Now that the previous patch gave objtool the ability to read retpoline
alternatives, it shows a new warning:

arch/x86/entry/entry_64.o: warning: objtool: .entry_trampoline: don't know how to handle alternatives at end of section

This is due to the JMP_NOSPEC in entry_SYSCALL_64_trampoline().

Previously, objtool ignored this situation because it wasn't needed, and
it would have required a bit of extra code. Now that this case exists,
add proper support for it.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
tools/objtool/check.c | 53 ++++++++++++++++++++++++++++++---------------------
1 file changed, 31 insertions(+), 22 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index bc3490d929ff..9cd028aa1509 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -594,7 +594,7 @@ static int handle_group_alt(struct objtool_file *file,
struct instruction *orig_insn,
struct instruction **new_insn)
{
- struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
+ struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
unsigned long dest_off;

last_orig_insn = NULL;
@@ -610,28 +610,30 @@ static int handle_group_alt(struct objtool_file *file,
last_orig_insn = insn;
}

- if (!next_insn_same_sec(file, last_orig_insn)) {
- WARN("%s: don't know how to handle alternatives at end of section",
- special_alt->orig_sec->name);
- return -1;
- }
-
- fake_jump = malloc(sizeof(*fake_jump));
- if (!fake_jump) {
- WARN("malloc failed");
- return -1;
+ if (next_insn_same_sec(file, last_orig_insn)) {
+ fake_jump = malloc(sizeof(*fake_jump));
+ if (!fake_jump) {
+ WARN("malloc failed");
+ return -1;
+ }
+ memset(fake_jump, 0, sizeof(*fake_jump));
+ INIT_LIST_HEAD(&fake_jump->alts);
+ clear_insn_state(&fake_jump->state);
+
+ fake_jump->sec = special_alt->new_sec;
+ fake_jump->offset = -1;
+ fake_jump->type = INSN_JUMP_UNCONDITIONAL;
+ fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
+ fake_jump->ignore = true;
}
- memset(fake_jump, 0, sizeof(*fake_jump));
- INIT_LIST_HEAD(&fake_jump->alts);
- clear_insn_state(&fake_jump->state);
-
- fake_jump->sec = special_alt->new_sec;
- fake_jump->offset = -1;
- fake_jump->type = INSN_JUMP_UNCONDITIONAL;
- fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
- fake_jump->ignore = true;

if (!special_alt->new_len) {
+ if (!fake_jump) {
+ WARN("%s: empty alternative at end of section",
+ special_alt->orig_sec->name);
+ return -1;
+ }
+
*new_insn = fake_jump;
return 0;
}
@@ -654,8 +656,14 @@ static int handle_group_alt(struct objtool_file *file,
continue;

dest_off = insn->offset + insn->len + insn->immediate;
- if (dest_off == special_alt->new_off + special_alt->new_len)
+ if (dest_off == special_alt->new_off + special_alt->new_len) {
+ if (!fake_jump) {
+ WARN("%s: alternative jump to end of section",
+ special_alt->orig_sec->name);
+ return -1;
+ }
insn->jump_dest = fake_jump;
+ }

if (!insn->jump_dest) {
WARN_FUNC("can't find alternative jump destination",
@@ -670,7 +678,8 @@ static int handle_group_alt(struct objtool_file *file,
return -1;
}

- list_add(&fake_jump->list, &last_new_insn->list);
+ if (fake_jump)
+ list_add(&fake_jump->list, &last_new_insn->list);

return 0;
}
--
2.14.3
\
 
 \ /
  Last update: 2018-01-30 05:02    [W:0.115 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site