linux-kernel - Re: [PATCH] recordmcount: avoid using ABS symbol as reference

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Message-ID: <20210607173138.3882-1-mark-pk.tsai@mediatek.com>
Date:   Tue, 8 Jun 2021 01:31:38 +0800
From:   Mark-PK Tsai <mark-pk.tsai@...iatek.com>
To:     <rostedt@...dmis.org>
CC:     <ardb@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-toolchains@...r.kernel.org>, <mark-pk.tsai@...iatek.com>,
        <matthias.bgg@...il.com>, <mhelsley@...are.com>,
        <peterz@...radead.org>, <samitolvanen@...gle.com>,
        <yj.chiang@...iatek.com>
Subject: Re: [PATCH] recordmcount: avoid using ABS symbol as reference

> On Mon, 7 Jun 2021 13:44:21 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > There's an extended section header index section for just that. And
> > recordmcount actually seems to use that as well.
> > 
> > I can't seem to find enough of the thread to figure out what the actual
> > problem is though. The lore archive doesn't have anything prior to this
> > message.
> > 
> > One should only use st_shndx when >SHN_UDEF and <SHN_LORESERVE. When
> > SHN_XINDEX, then use .symtab_shndx.
> > 
> > Apparently you've found a case where neither is true? In that case
> > objtool seems to use shndx 0. A matching recordmcount patch would be
> > something like this.

Hi Peter,

Should I resend the below patch as v2?

> 
> Mark-PK,
> 
> Does the below patch fix it for you too (if you backport it to your
> kernel). I much rather have recordmcount match objtool, as one day the
> two will hopefully merge to one executable.
> 
> -- Steve
> 

Yes, this patch fix it.

> 
> > 
> > 
> > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
> > index f9b19524da11..d99cc0aed6fe 100644
> > --- a/scripts/recordmcount.h
> > +++ b/scripts/recordmcount.h
> > @@ -194,13 +194,18 @@ static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab,
> >  	unsigned long offset;
> >  	int index;
> >  
> > -	if (sym->st_shndx != SHN_XINDEX)
> > +	if (sym->st_shndx > SHN_UDEF &&
> > +	    sym->st_shndx < SHN_LORESERVE)
> >  		return w2(sym->st_shndx);
> >  
> > -	offset = (unsigned long)sym - (unsigned long)symtab;
> > -	index = offset / sizeof(*sym);
> > +	if (sym->st_shndx == SHN_XINDEX) {
> > +		offset = (unsigned long)sym - (unsigned long)symtab;
> > +		index = offset / sizeof(*sym);
> >  
> > -	return w(symtab_shndx[index]);
> > +		return w(symtab_shndx[index]);
> > +	}
> > +
> > +	return 0;
> >  }
> >  
> >  static unsigned int get_shnum(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0)