objtool, modules: Discard objtool annotation sections for modules

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@linux-foundation.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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@kernel.org>

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index ad0118f..c74ae9c 100644 (file)
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -345,8 +345,6 @@ SECTIONS
        DISCARDS
        /DISCARD/ : {
                *(.eh_frame)
-               *(__func_stack_frame_non_standard)
-               *(__unreachable)
        }
 }
 

diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index b6bb901..0efef9c 100644 (file)
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -200,7 +200,7 @@
 #ifdef CONFIG_STACK_VALIDATION
 #define annotate_unreachable() ({                                      \
        asm("%c0:\t\n"                                                  \
-           ".pushsection __unreachable, \"a\"\t\n"                     \
+           ".pushsection .discard.unreachable\t\n"                     \
            ".long %c0b - .\t\n"                                        \
            ".popsection\t\n" : : "i" (__LINE__));                      \
 })

diff --git a/include/linux/frame.h b/include/linux/frame.h
index e6baaba..d772c61 100644 (file)
--- 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 */

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 4dedd0d..30d752a 100644 (file)
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -854,6 +854,7 @@ static const char *const section_white_list[] =
        ".cmem*",                       /* EZchip */
        ".fmt_slot*",                   /* EZchip */
        ".gnu.lto*",
+       ".discard.*",
        NULL
 };
 

diff --git a/scripts/module-common.lds b/scripts/module-common.lds
index 73a2c7d..cf7e52e 100644 (file)
--- 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+*)) }

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 5fc52ee..4cfdbb5 100644 (file)
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -339,13 +339,13 @@ static int add_dead_ends(struct objtool_file *file)
        struct instruction *insn;
        bool found;
 
-       sec = find_section_by_name(file->elf, ".rela__unreachable");
+       sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
        if (!sec)
                return 0;
 
        list_for_each_entry(rela, &sec->rela_list, list) {
                if (rela->sym->type != STT_SECTION) {
-                       WARN("unexpected relocation symbol type in .rela__unreachable");
+                       WARN("unexpected relocation symbol type in %s", sec->name);
                        return -1;
                }
                insn = find_insn(file, rela->sym->sec, rela->addend);
@@ -1272,7 +1272,7 @@ int cmd_check(int argc, const char **argv)
 
        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");