[tip:core/objtool] objtool: Add STACK_FRAME_NON_STANDARD() macro

[tip-bot for Josh Poimboeuf]

Commit-ID:  9a99417acbad99ba6c6a9389b45a53a4d002bb7e
Gitweb:     http://git.kernel.org/tip/9a99417acbad99ba6c6a9389b45a53a4d002bb7e
Author:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Sun, 28 Feb 2016 22:22:35 -0600
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 29 Feb 2016 08:35:10 +0100

objtool: Add STACK_FRAME_NON_STANDARD() macro

Add a new macro, STACK_FRAME_NON_STANDARD(), which is used to denote a
function which does something unusual related to its stack frame.  Use
of the macro prevents objtool from emitting a false positive warning.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Bernd Petrovitsch <bernd@xxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Marek <mmarek@xxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxx>
Cc: Pedro Alves <palves@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: live-patching@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/34487a17b23dba43c50941599d47054a9584b219.1456719558.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/kernel/vmlinux.lds.S |  5 ++++-
 include/linux/frame.h         | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 92dc211..13fa0ad 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -343,7 +343,10 @@ SECTIONS
 
 	/* Sections to be discarded */
 	DISCARDS
-	/DISCARD/ : { *(.eh_frame) }
+	/DISCARD/ : {
+		*(.eh_frame)
+		*(__func_stack_frame_non_standard)
+	}
 }
 
 
diff --git a/include/linux/frame.h b/include/linux/frame.h
new file mode 100644
index 0000000..e6baaba
--- /dev/null
+++ b/include/linux/frame.h
@@ -0,0 +1,23 @@
+#ifndef _LINUX_FRAME_H
+#define _LINUX_FRAME_H
+
+#ifdef CONFIG_STACK_VALIDATION
+/*
+ * This macro marks the given function's stack frame as "non-standard", which
+ * tells objtool to ignore the function when doing stack metadata validation.
+ * It should only be used in special cases where you're 100% sure it won't
+ * affect the reliability of frame pointers and kernel stack traces.
+ *
+ * For more information, see tools/objtool/Documentation/stack-validation.txt.
+ */
+#define STACK_FRAME_NON_STANDARD(func) \
+	static void __used __section(__func_stack_frame_non_standard) \
+		*__func_stack_frame_non_standard_##func = func
+
+#else /* !CONFIG_STACK_VALIDATION */
+
+#define STACK_FRAME_NON_STANDARD(func)
+
+#endif /* CONFIG_STACK_VALIDATION */
+
+#endif /* _LINUX_FRAME_H */