Re: [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time

Alexander Lobakin
2021-01-06T20:29:50Z

From: Nathan Chancellor <natechancellor@gmail.com>
Date: Wed, 6 Jan 2021 13:23:24 -0700

On Wed, Jan 06, 2021 at 08:08:29PM +0000, Alexander Lobakin wrote:
>> Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn
>> or .rela.dyn and check for these sections to be zero-sized
>> at link time.
>>
>> At least two of them were noticed in real builds:
>>
>> mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn'
>> from `init/main.o' being placed in section `.rel.dyn'
>>
>> ld.lld: warning: <internal>:(.got) is being placed in '.got'
>>
>> Adopted from x86/kernel/vmlinux.lds.S.
>>
>> Reported-by: Nathan Chancellor <natechancellor@gmail.com> # .got
>> Suggested-by: Fangrui Song <maskray@google.com> # .rel.dyn
>> Signed-off-by: Alexander Lobakin <alobakin@pm.me>
>> ---
>> arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++
>> 1 file changed, 35 insertions(+)
>>
>> diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
>> index 5d6563970ab2..05eda9d9a7d5 100644
>> --- a/arch/mips/kernel/vmlinux.lds.S
>> +++ b/arch/mips/kernel/vmlinux.lds.S
>> @@ -227,4 +227,39 @@ SECTIONS
>> *(.pdr)
>> *(.reginfo)
>> }
>> +
>> + /*
>> + * Sections that should stay zero sized, which is safer to
>> + * explicitly check instead of blindly discarding.
>> + */
>> +
>> + .got : {
>> + *(.got)
>> + *(.igot.*)
>> + }
>> + ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
>
> This assertion does trigger now.
>
> $ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- LLVM=1 \
> O=out/mipsel distclean malta_kvm_guest_defconfig all
> ...
> ld.lld: error: Unexpected GOT entries detected!
> ld.lld: error: Unexpected GOT entries detected!
> ...

Oops. I'll build my kernel with LLVM stack and dig into it deeper
tomorrow.

>> + .got.plt (INFO) : {
>> + *(.got.plt)
>> + }
>> + ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
>> +
>> + .plt : {
>> + *(.plt)
>> + *(.plt.*)
>> + *(.iplt)
>> + }
>> + ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
>> +
>> + .rel.dyn : {
>> + *(.rel.*)
>> + *(.rel_*)
>> + }
>> + ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
>> +
>> + .rela.dyn : {
>> + *(.rela.*)
>> + *(.rela_*)
>> + }
>> + ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
>> }
>> --
>> 2.30.0

Thanks,
Al