Fix for objtool/module breakage

2 files changed, 156 insertions, 0 deletions

diff --git a/kernel.spec b/kernel.spec
index 73f2a3204..08b1b2cca 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -602,6 +602,9 @@ Patch666: ccm-stack.patch
 # grabbed from mailing list
 Patch667: v3-Revert-tty-serial-pl011-add-ttyAMA-for-matching-pl011-console.patch
 
+# reported via IRC
+Patch668: objtool-fix.patch
+
 # END OF PATCH DEFINITIONS
 
 %endif
diff --git a/objtool-fix.patch b/objtool-fix.patch
new file mode 100644
index 000000000..fcf0c9956
--- /dev/null
+++ b/objtool-fix.patch
@@ -0,0 +1,153 @@
+From 898d20ca04d5a13dcca5483ed5213ad92fed88d3 Mon Sep 17 00:00:00 2001
+From: Josh Poimboeuf <jpoimboe@redhat.com>
+Date: Wed, 1 Mar 2017 00:05:04 -0600
+Subject: [PATCH] objtool fixes
+
+On Tue, Feb 28, 2017 at 05:55:11PM -0800, Linus Torvalds wrote:
+> Guys,
+>  the recent 'objtool' pull request broke things.
+>
+> I haven't bisected it, but I'm pretty sure that this part is pure garbage:
+>
+> On Mon, Feb 27, 2017 at 11:53 PM, Ingo Molnar <mingo@kernel.org> wrote:
+> >
+> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
+> > index e79f15f108a8..ad0118fbce90 100644
+> > --- a/arch/x86/kernel/vmlinux.lds.S
+> > +++ b/arch/x86/kernel/vmlinux.lds.S
+> > @@ -346,6 +346,7 @@ SECTIONS
+> >         /DISCARD/ : {
+> >                 *(.eh_frame)
+> >                 *(__func_stack_frame_non_standard)
+> > +               *(__unreachable)
+> >         }
+> >  }
+> >
+> > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
+> > index 0444b1336268..f457b520ead6 100644
+> > --- a/include/linux/compiler-gcc.h
+> > +++ b/include/linux/compiler-gcc.h
+> > @@ -195,6 +195,17 @@
+> >  #endif
+> >  #endif
+> >
+> > +#ifdef CONFIG_STACK_VALIDATION
+> > +#define annotate_unreachable() ({                                      \
+> > +       asm("%c0:\t\n"                                                  \
+> > +           ".pushsection __unreachable, \"a\"\t\n"                     \
+> > +           ".long %c0b\t\n"                                            \
+> > +           ".popsection\t\n" : : "i" (__LINE__));                      \
+> > +})
+> > +#else
+> > +#define annotate_unreachable()
+> > +#endif
+>
+> and I think the above is what breaks module loading for me right now
+> on my laptop.
+>
+> I get this during bootup:
+>
+>     module: overflow in relocation type 10 val ffffffffc02afc81
+>     module: 'nvme' likely not compiled with -mcmodel=kernel
+>
+> (and similar errors for other modules too), but those modules very
+> much *are* compiled with all the normal kernel build flags, including
+> -mcmodel=kernel.
+>
+> Now, relocation type 10 is R_X86_64_32, so the warning is very true:
+> that address would fit in a _signed_ 32-bit value, but that's
+> supposedly a 32-bit unsigned relocation.
+>
+> Trying to figure out what the hell is going on, I do:
+>
+>     objdump -r nvme.ko | grep 64_32
+>
+> and what do I find? I find
+>
+>   RELOCATION RECORDS FOR [__unreachable]:
+>   OFFSET           TYPE              VALUE
+>   0000000000000000 R_X86_64_32       .text+0x0000000000000c81
+>   0000000000000004 R_X86_64_32       .text+0x0000000000000cb5
+>   0000000000000008 R_X86_64_32       .text+0x0000000000001a18
+>   000000000000000c R_X86_64_32       .text+0x0000000000001a36
+>   0000000000000010 R_X86_64_32       .text+0x0000000000001e38
+>   0000000000000014 R_X86_64_32       .text+0x0000000000001ec2
+>   0000000000000018 R_X86_64_32       .text+0x00000000000034e2
+>   000000000000001c R_X86_64_32       .text+0x0000000000003536
+>
+> and then when I look more closely (objdump --disassemble), I see that
+> the offset 000c81 in the module refers to this:
+>
+>   0000000000000c60 <nvme_admin_init_request>:
+>         ....
+>      c7f:       0f 0b                   ud2
+>      c81:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
+>
+> so it very much looks like those relocations are still around on
+> modules, and so module loading fails.
+>
+> Anyway, those annotations are completely bogus anyway, it looks. You
+> guys should use relative offsets in order to be able to specify a
+> kernel address. So doing
+>
+>     .long %c0
+>
+> is garbage - either it needs to be a .quad, or it needs to be relative
+> to the text section to fit in a .long.
+>
+> Hmm? Revert or fix, but please quickly...
+
+Yuck, sorry about that.  Patch to fix it below.
+
+This also highlights another (minor) issue: the '__unreachable' section
+is meant to be a compile-time-only thing.  It's supposed to be discarded
+at link time, but apparently that isn't happening for modules.
+
+I tried excluding it from linking with the .pushsection "e" flag, but no
+luck.  I'll try to figure out how to fix that shortly.
+
+In the meantime, here's the fix you need.  It now uses X86_64_64
+relocations.
+
+----
+
+From: Josh Poimboeuf <jpoimboe@redhat.com>
+Subject: [PATCH] objtool: fix __unreachable section relocation size
+
+Linus reported the following commit broke module loading on his laptop:
+
+  d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")
+
+It showed errors like the following:
+
+  module: overflow in relocation type 10 val ffffffffc02afc81
+  module: 'nvme' likely not compiled with -mcmodel=kernel
+
+The problem is that the __unreachable section addresses are stored using
+the '.long' asm directive, which isn't big enough for .text section
+relative kernel addresses.  Use '.quad' instead.
+
+Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
+Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
+Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")
+Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
+---
+ include/linux/compiler-gcc.h | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
+index 76e28c2..91a77a5 100644
+--- a/include/linux/compiler-gcc.h
++++ b/include/linux/compiler-gcc.h
+@@ -201,7 +201,7 @@
+ #define annotate_unreachable() ({					\
+ 	asm("%c0:\t\n"							\
+ 	    ".pushsection __unreachable, \"a\"\t\n"			\
+-	    ".long %c0b\t\n"						\
++	    ".quad %c0b\t\n"						\
+ 	    ".popsection\t\n" : : "i" (__LINE__));			\
+ })
+ #else
+-- 
+2.7.4
+