[PATCH 4.9 81/96] objtool, modules: Discard objtool annotation sections for modules

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

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

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

commit e390f9a9689a42f477a6073e2e7df530a4c1b740 upstream.

The '__unreachable' and '__func_stack_frame_non_standard' sections are
only used at compile time.  They're discarded for vmlinux but they
should also be discarded for modules.

Since this is a recurring pattern, prefix the section names with
".discard.".  It's a nice convention and vmlinux.lds.h already discards
such sections.

Also remove the 'a' (allocatable) flag from the __unreachable section
since it doesn't make sense for a discarded section.

Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Jessica Yu <jeyu@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")
Link: http://lkml.kernel.org/r/20170301180444.lhd53c5tibc4ns77@treble
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
[dwmw2: Remove the unreachable part in backporting since it's not here yet]
Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/frame.h         |    2 +-
 scripts/mod/modpost.c         |    1 +
 scripts/module-common.lds     |    5 ++++-
 tools/objtool/builtin-check.c |    2 +-
 4 files changed, 7 insertions(+), 3 deletions(-)

--- a/include/linux/frame.h
+++ b/include/linux/frame.h
@@ -11,7 +11,7 @@
  * 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) \
+	static void __used __section(.discard.func_stack_frame_non_standard) \
 		*__func_stack_frame_non_standard_##func = func
 
 #else /* !CONFIG_STACK_VALIDATION */
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -838,6 +838,7 @@ static const char *const section_white_l
 	".cmem*",			/* EZchip */
 	".fmt_slot*",			/* EZchip */
 	".gnu.lto*",
+	".discard.*",
 	NULL
 };
 
--- a/scripts/module-common.lds
+++ b/scripts/module-common.lds
@@ -4,7 +4,10 @@
  * combine them automatically.
  */
 SECTIONS {
-	/DISCARD/ : { *(.discard) }
+	/DISCARD/ : {
+		*(.discard)
+		*(.discard.*)
+	}
 
 	__ksymtab		0 : { *(SORT(___ksymtab+*)) }
 	__ksymtab_gpl		0 : { *(SORT(___ksymtab_gpl+*)) }
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -1229,7 +1229,7 @@ int cmd_check(int argc, const char **arg
 
 	INIT_LIST_HEAD(&file.insn_list);
 	hash_init(file.insn_hash);
-	file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
+	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
 	file.rodata = find_section_by_name(file.elf, ".rodata");
 	file.ignore_unreachables = false;
 	file.c_file = find_section_by_name(file.elf, ".comment");