linux-kernel - [PATCH] x86: Discard .note.gnu.property sections

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Message-Id: <20180924201459.35923-1-hjl.tools@gmail.com>
Date:   Mon, 24 Sep 2018 13:14:59 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [PATCH] x86: Discard .note.gnu.property sections

With the command-line option, -mx86-used-note=yes, the x86 assembler
in binutils 2.32 and above generates a program property note in a note
section, .note.gnu.property, to encode used x86 ISAs and features.
To exclude .note.gnu.property sections from NOTE segment in x86 kernel
linker script:

PHDRS {
 text PT_LOAD FLAGS(5);
 data PT_LOAD FLAGS(6);
 percpu PT_LOAD FLAGS(6);
 init PT_LOAD FLAGS(7);
 note PT_NOTE FLAGS(0);
}
SECTIONS
{
...
 .notes : AT(ADDR(.notes) - 0xffffffff80000000) { __start_notes = .; KEEP(*(.not
e.*)) __stop_notes = .; } :text :note
...
}

this patch discards .note.gnu.property sections in kernel linker script
by adding

 /DISCARD/ : {
  *(.note.gnu.property)
 }

before .notes sections.  Since .exit.text and .exit.data sections are
discarded at runtime, it undefines EXIT_TEXT and EXIT_DATA to exclude
.exit.text and .exit.data sections from default discarded sections.

Signed-off-by: H.J. Lu <hjl.tools@...il.com>
---
 arch/x86/kernel/vmlinux.lds.S | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 8bde0a419f86..7e1e0ef1578a 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -138,6 +138,10 @@ SECTIONS
 		_etext = .;
 	} :text = 0x9090

+	/* .note.gnu.property sections should be discarded */
+	/DISCARD/ : {
+		*(.note.gnu.property)
+	}
 	NOTES :text :note

 	EXCEPTION_TABLE(16) :text = 0x9090
@@ -373,7 +377,12 @@ SECTIONS
 	STABS_DEBUG
 	DWARF_DEBUG

-	/* Sections to be discarded */
+	/* Sections to be discarded.  EXIT_TEXT and EXIT_DATA discard at runtime.
+	 * not link time.  */
+#undef EXIT_TEXT
+#define EXIT_TEXT
+#undef EXIT_DATA
+#define EXIT_DATA
 	DISCARDS
 	/DISCARD/ : {
 		*(.eh_frame)
-- 
2.17.1