From: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
To: <ardb@kernel.org>
Cc: <linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>,
<linux-mediatek@lists.infradead.org>, <mark-pk.tsai@mediatek.com>,
<matthias.bgg@gmail.com>, <mhelsley@vmware.com>,
<rostedt@goodmis.org>, <samitolvanen@google.com>,
<yj.chiang@mediatek.com>
Subject: Re: [PATCH] recordmcount: avoid using ABS symbol as reference
Date: Mon, 7 Jun 2021 14:59:48 +0800 [thread overview]
Message-ID: <20210607065948.31632-1-mark-pk.tsai@mediatek.com> (raw)
In-Reply-To: <CAMj1kXE3faN7nSSdoSU=ed+OPruefD_vJuhyRnsMuNiRygZZbg@mail.gmail.com>
> > 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.
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.
>
> > 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.
>
> > 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 6:59 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 [this message]
2021-06-07 7:07 ` Ard Biesheuvel
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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