Messages in this thread | | | From | Mark-PK Tsai <> | Subject | Re: [PATCH] recordmcount: avoid using ABS symbol as reference | Date | Mon, 7 Jun 2021 14:59:48 +0800 |
| |
> > 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)) {
| |