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

Fāng-ruì Sòng
2021-01-06T20:23:02Z

On Wed, Jan 6, 2021 at 12:08 PM Alexander Lobakin <alobakin@pm.me> 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!")
> +
> + .got.plt (INFO) : {
> + *(.got.plt)
> + }
> + ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")

(INFO) drops the SHF_ALLOC flag from the output section (It does not
mean "informational"). INFO is not need here.
The diff from 815d680771ae09080d2da83dac2647c08cdf99ce "x86/build:
Enforce an empty .got.plt section" is not needed.

> + .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!")
> }

x86 has both .rel.dyn and .rela.dyn because i386 psABI uses REL while
x86-64 psABI uses RELA, but mips does not need .rela.dyn

> --
> 2.30.0
>
>