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Commit 17bc3391 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
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objtool: Add support for alternatives at the end of a section 



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: default avatarJosh 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: default avatarIngo Molnar <mingo@kernel.org>
parent a845c7cf

tools/objtool/check.c

+31 −22
Original line number Diff line number Diff line
@@ -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;
@@ -610,12 +610,7 @@ 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;

	}



	if (next_insn_same_sec(file, last_orig_insn)) {

		fake_jump = malloc(sizeof(*fake_jump));

		if (!fake_jump) {

			WARN("malloc failed");
@@ -630,8 +625,15 @@ static int handle_group_alt(struct objtool_file *file, 
		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",
@@ -670,6 +678,7 @@ static int handle_group_alt(struct objtool_file *file, 
		return -1;

	}



	if (fake_jump)

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



	return 0;