linux-kernel - Re: [tip: objtool/urgent] objtool: Fix seg fault with Clang non-section symbols

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Message-ID: <20210215162209.5e2a475b@gandalf.local.home>
Date:   Mon, 15 Feb 2021 16:22:09 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Xi Ruoyao <xry111@...gyan1223.wang>,
        "# 3.4.x" <stable@...r.kernel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Miroslav Benes <mbenes@...e.cz>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip: objtool/urgent] objtool: Fix seg fault with Clang
 non-section symbols

On Mon, 15 Feb 2021 09:58:06 -0600
Josh Poimboeuf <jpoimboe@...hat.com> wrote:

> On Mon, Feb 15, 2021 at 09:53:07AM -0500, Steven Rostedt wrote:
> > On Sun, 14 Feb 2021 09:51:47 -0600
> > Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >   
> > > Steve, looks like recordmcount avoids referencing weak symbols directly
> > > by their function symbol.  Maybe it can just skip weak symbols which
> > > don't have a section symbol, since this seems like a rare scenario.  
> > 
> > When does the .text.unlikely section disappear? During the creation of the
> > object, or later in the linker stage?  
> 
> The section is there, but the symbol associated with the section
> (".text.unlikely" symbol) isn't generated by the assembler.
> 

Greg,

Does this fix the issue with you? It appears to fix it for my arch linux
VM that I created that uses binutils 2.36-3.

-- Steve

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index f9b19524da11..558b67f8364e 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -562,7 +562,7 @@ static char const * __has_rel_mcount(Elf_Shdr const *const relhdr, /* reltype */
 	if (w(txthdr->sh_type) != SHT_PROGBITS ||
 	    !(_w(txthdr->sh_flags) & SHF_EXECINSTR))
 		return NULL;
-	return txtname;
+	return shdr0->sh_size ? txtname : NULL;
 }
 
 static char const *has_rel_mcount(Elf_Shdr const *const relhdr,