linux-kernel - Re: objtool warning breaks build for fs/dlm/lock.o

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Date:   Mon, 18 May 2020 21:57:50 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: objtool warning breaks build for fs/dlm/lock.o

On Fri, May 8, 2020 at 1:29 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> On Wed, May 06, 2020 at 04:07:25PM +0200, Arnd Bergmann wrote:
> > Hi,
> >
> > During randconfig testing with clang-10 I came across a number
> > of additional objtool warnings, I'll send another mail about those
> > when I have collected more information and some object files.
> >
> > This one sticks out however, as objtool returns an error code that
> > stops the build:
>
> > fs/dlm/lock.o: warning: objtool: __receive_convert_reply()+0x1e5: can't find jump dest instruction at .text+0xcaa7
>
> Thanks for sending the patch for this one.  Objtool always gets confused
> by new compiler versions, I really think we need to revert
>
>   644592d32837 ("objtool: Fail the kernel build on fatal errors")
>
> because objtool is never going to be reliable enough such that we can be
> confident that failing the build is the right thing to do.

I'm now struggling with a clang -fintegrated-as related failure:

arch/x86/kernel/ftrace_64.o: warning: objtool: missing symbol for insn
at offset 0x16
make[4]: *** [/git/arm-soc/scripts/Makefile.build:355:
arch/x86/kernel/ftrace_64.o] Error 255

Using this as a local workaround, but I'd like to find out if this is a bug
in clang or in objtool:

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index e77261db2391..b4a0f3dd321d 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -38,6 +38,9 @@ OBJECT_FILES_NON_STANDARD_paravirt_patch.o            := y
 ifdef CONFIG_FRAME_POINTER
 OBJECT_FILES_NON_STANDARD_ftrace_$(BITS).o             := y
 endif
+ifdef CONFIG_CC_IS_CLANG
+AFLAGS_ftrace_64.o                                     += -fno-integrated-as
+endif

 # If instrumentation of this dir is enabled, boot hangs during first second.
 # Probably could be more selective here, but note that files related to irqs,

Attaching the broken object file fore reference.

     Arnd

Download attachment "ftrace_64.o" of type "application/x-object" (1040 bytes)