From: Ard Biesheuvel <ardb@kernel.org>
To: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-mediatek@lists.infradead.org,
Matthias Brugger <matthias.bgg@gmail.com>,
Matt Helsley <mhelsley@vmware.com>,
"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
Sami Tolvanen <samitolvanen@google.com>,
yj.chiang@mediatek.com
Subject: Re: [PATCH] recordmcount: avoid using ABS symbol as reference
Date: Mon, 7 Jun 2021 09:07:25 +0200 [thread overview]
Message-ID: <CAMj1kXFPuWLkORrT4YUfoKZ6+SsLRjxdNM91iff4SJj2jgWa8A@mail.gmail.com> (raw)
In-Reply-To: <20210607065948.31632-1-mark-pk.tsai@mediatek.com>
On Mon, 7 Jun 2021 at 08:59, Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:
>
> > > On Mon, 7 Jun 2021 at 04:42, Mark-PK Tsai <mark-pk.tsai@mediatek.com> wrote:
> > >
> > > Avoid using ABS symbol, which won't be relocate, as reference.
> > >
> > > On arm64 platform, if there's shndx equals SHN_ABS(0xfff1).
> > >
> > > Section Headers:
> > > [Nr] Name Type Address Off Size ES Flg Lk Inf Al
> > > [65521] .text.n_tty_receive_buf PROGBITS 0000000000000000 3cdab520 000054 00 AX 0 0 4
> > > [65522] .rela.text.n_tty_receive_buf RELA 0000000000000000 3cdab578 000030 18 I 152076 65521 8
> > >
> >
> > A RELA section's r_info field points to the section to which it
> > applies. This is why in the example above section #65522 points to
> > section #65521. This has nothing to do with the numerical value of
> > SHN_ABS.
>
> If the r_info of RELA section is 65521(0xfff1),
> find_secsym_ndx() will use it to find the base symbol.
>
But what does that have to do with the sh_info field of the RELA
section's Elf_Shdr struct? IOW, what is the relevance of section
#65521 here?
> And in the symbol search loop in find_secsym_ndx(), get_symindex will
> return 0xfff1 if the symbol is in ABS section.
>
> In this case, find_secsym_ndx() will return a absolute symbol as
> base, which won't be relocate, if an ABS symbol is found before the
> real symbol in section 65521.
>
I see your point here.
> >
> > > find_secsym_ndx, which use r_info in rela section to find the reference
> > > symbol, may take ABS symbol as base.
> > >
> > > Symbol table '.symtab' contains 453285 entries:
> > > Num: Value Size Type Bind Vis Ndx Name
> > > 6: 0000000000000002 0 NOTYPE LOCAL DEFAULT ABS section_count
> > >
> > > Which cause an invalid address in __mcount_loc.
> > >
> >
> > Could you give a better account of the error you are trying to address?
> >
> > Also, arm64 no longer defines a section_count symbol (since v5.11), so
> > please make sure that the diagnostics of the issue you are addressing
> > are accurate for mainline.
> >
>
> My kernel version is 5.4.61.
> But as I explained, I suppose mainline also have this issue.
>
Mainline is what we work on. So please base your changes (and your
commit log) on mainline.
> >
> > > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
> > > ---
> > > scripts/recordmcount.h | 4 ++++
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
> > > index f9b19524da11..9b69167fb7ff 100644
> > > --- a/scripts/recordmcount.h
> > > +++ b/scripts/recordmcount.h
> > > @@ -526,6 +526,10 @@ static int find_secsym_ndx(unsigned const txtndx,
> > > for (symp = sym0, t = nsym; t; --t, ++symp) {
> > > unsigned int const st_bind = ELF_ST_BIND(symp->st_info);
> > >
> > > + /* avoid absolute symbols */
> > > + if (symp->st_shndx == SHN_ABS)
> > > + continue;
> > > +
> > > if (txtndx == get_symindex(symp, symtab, symtab_shndx)
> > > /* avoid STB_WEAK */
> > > && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
next prev parent reply other threads:[~2021-06-07 7:07 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-07 2:38 [PATCH] recordmcount: avoid using ABS symbol as reference Mark-PK Tsai
2021-06-07 6:37 ` Ard Biesheuvel
2021-06-07 6:59 ` Mark-PK Tsai
2021-06-07 7:07 ` Ard Biesheuvel [this message]
2021-06-07 7:42 ` Mark-PK Tsai
2021-06-07 8:06 ` Mark-PK Tsai
2021-06-07 9:50 ` Ard Biesheuvel
2021-06-07 10:32 ` Mark-PK Tsai
2021-06-07 11:44 ` Peter Zijlstra
2021-06-07 13:18 ` Mark-PK Tsai
2021-06-07 13:44 ` Steven Rostedt
2021-06-07 17:31 ` Mark-PK Tsai
2021-06-07 15:40 ` Peter Zijlstra
2021-06-08 1:15 ` Mark-PK Tsai
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