linux-kernel - [PATCH] x86/build: Simplify patterns for unwanted section

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Date: Wed, 14 Feb 2024 13:29:29 -0800
From: Fangrui Song <maskray@...gle.com>
To: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>, 
	llvm@...ts.linux.dev, Nathan Chancellor <nathan@...nel.org>, 
	Heiko Carstens <hca@...ux.ibm.com>, Fangrui Song <maskray@...gle.com>
Subject: [PATCH] x86/build: Simplify patterns for unwanted section

A s390 patch modeling its --orphan-handling= after x86 [1] sparked my
motivation to simplify patterns. Commit 5354e84598f2 ("x86/build: Add
asserts for unwanted sections") added asserts that certain input
sections must be absent or empty. The patterns can be simplified.

For dynamic relocations,

*(.rela.*) is sufficient to match all dynamic relocations synthesized by
GNU ld and LLD. .rela_* is unnecessary. --emit-relocs may create .rela_*
sections for section names prefixed with _, but they are not matched by
linker scripts.

plt instead of .plt.* is sufficient to match synthesized PLT entries.

igot and .igot.plt are for non-preemptible STT_GNU_IFUNC in GNU ld (LLD
just uses .got), which the kernel does not use. In addition, if .igot or
igot.plt is ever non-empty, there will be .rela.* dynamic relocations
leading to an assert failure anyway.

[1]: https://lore.kernel.org/all/20240207-s390-lld-and-orphan-warn-v1-6-8a665b3346ab@kernel.org/

Signed-off-by: Fangrui Song <maskray@...gle.com>
---
 arch/x86/boot/compressed/vmlinux.lds.S | 6 +++---
 arch/x86/kernel/vmlinux.lds.S          | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 083ec6d7722a..9f288f67972a 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -104,17 +104,17 @@ SECTIONS
 	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
 
 	.plt : {
-		*(.plt) *(.plt.*)
+		*(.plt)
 	}
 	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
 
 	.rel.dyn : {
-		*(.rel.*) *(.rel_*)
+		*(.rel.*)
 	}
 	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
 
 	.rela.dyn : {
-		*(.rela.*) *(.rela_*)
+		*(.rela.*)
 	}
 	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
 }
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index a349dbfc6d5a..b3da7b81d2b3 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -463,22 +463,22 @@ SECTIONS
 	 * explicitly check instead of blindly discarding.
 	 */
 	.got : {
-		*(.got) *(.igot.*)
+		*(.got)
 	}
 	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
 
 	.plt : {
-		*(.plt) *(.plt.*) *(.iplt)
+		*(.plt)
 	}
 	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
 
 	.rel.dyn : {
-		*(.rel.*) *(.rel_*)
+		*(.rel.*)
 	}
 	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
 
 	.rela.dyn : {
-		*(.rela.*) *(.rela_*)
+		*(.rela.*)
 	}
 	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
 }
-- 
2.43.0.687.g38aa6559b0-goog