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

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Message-ID: <20200518230424.rftemp76uch4piy7@treble>
Date:   Mon, 18 May 2020 18:04:24 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Arnd Bergmann <arnd@...db.de>
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 Mon, May 18, 2020 at 05:53:28PM -0500, Josh Poimboeuf wrote:
> > 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:
> 
> It seems like an objtool bug, though at first glance I don't know where
> exactly.  It could be a problem with the rb-tree stuff Peter added
> recently.
> 
> That instruction should be part of the __fentry__ function:
> 
>      4: 0000000000000000   165 FUNC    GLOBAL DEFAULT    3 __fentry__
> 
> So find_symbol_containing() should associate it with __fentry__.

Peter, is find_symbol_containing() broken by aliased functions and/or
overlapping symbols?

Symbol table '.symtab' contains 7 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT    5 __ksym_marker___fentry__
     2: 000000000000000e     0 NOTYPE  LOCAL  DEFAULT    3 fgraph_trace
     3: 000000000000000f     0 NOTYPE  LOCAL  DEFAULT    3 trace
     4: 0000000000000000   165 FUNC    GLOBAL DEFAULT    3 __fentry__
     5: 000000000000000e     0 NOTYPE  GLOBAL DEFAULT    3 ftrace_stub
     6: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND ftrace_trace_function

Notice the NOTYPEs are inside the FUNC.

-- 
Josh