From: Nathan Chancellor <redacted>
Date: Wed, 6 Jan 2021 13:23:24 -0700

On Wed, Jan 06, 2021 at 08:08:29PM +0000, Alexander Lobakin wrote:

quoted

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 <redacted> # .got
Suggested-by: Fangrui Song <redacted> # .rel.dyn
Signed-off-by: Alexander Lobakin <redacted>
---
 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.

quoted

+	.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