linux-kernel - [PATCH 5.12 262/700] kbuild: Fix objtool dependency for OBJECT_FILES_NON_STANDARD

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Date:   Mon, 12 Jul 2021 08:05:45 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.12 262/700] kbuild: Fix objtool dependency for OBJECT_FILES_NON_STANDARD_<obj> := n

From: Josh Poimboeuf <jpoimboe@...hat.com>

[ Upstream commit 8852c552402979508fdc395ae07aa8761aa46045 ]

"OBJECT_FILES_NON_STANDARD_vma.o := n" has a dependency bug.  When
objtool source is updated, the affected object doesn't get re-analyzed
by objtool.

Peter's new variable-sized jump label feature relies on objtool
rewriting the object file.  Otherwise the system can fail to boot.  That
effectively upgrades this minor dependency issue to a major bug.

The problem is that variables in prerequisites are expanded early,
during the read-in phase.  The '$(objtool_dep)' variable indirectly uses
'$@', which isn't yet available when the target prerequisites are
evaluated.

Use '.SECONDEXPANSION:' which causes '$(objtool_dep)' to be expanded in
a later phase, after the target-specific '$@' variable has been defined.

Fixes: b9ab5ebb14ec ("objtool: Add CONFIG_STACK_VALIDATION option")
Fixes: ab3257042c26 ("jump_label, x86: Allow short NOPs")
Reported-by: Matthew Wilcox <willy@...radead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 scripts/Makefile.build | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 1b6094a13034..73701d637ed5 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -267,7 +267,8 @@ define rule_as_o_S
 endef

 # Built-in and composite module parts
-$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
+.SECONDEXPANSION:
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE
 	$(call if_changed_rule,cc_o_c)
 	$(call cmd,force_checksrc)

@@ -348,7 +349,7 @@ cmd_modversions_S =								\
 	fi
 endif

-$(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
+$(obj)/%.o: $(src)/%.S $$(objtool_dep) FORCE
 	$(call if_changed_rule,as_o_S)

 targets += $(filter-out $(subdir-builtin), $(real-obj-y))
-- 
2.30.2