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Subject[PATCH 4.14 29/64] objtool: Add support for alternatives at the end of a section
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josh Poimboeuf jpoimboe@redhat.com

commit 17bc33914bcc98ba3c6b426fd1c49587a25c0597

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>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2a30a3c2158af47d891a76e69bb1ef347e0443fd.1517284349.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
tools/objtool/check.c | 53 +++++++++++++++++++++++++++++---------------------
1 file changed, 31 insertions(+), 22 deletions(-)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -594,7 +594,7 @@ static int handle_group_alt(struct objto
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 objto
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 objto
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 objto
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;
}

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