linux-kernel - [PATCH] arm64: lds: move .got section out of .text

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Message-ID: <20230428050442.180913-1-maskray@google.com>
Date:   Fri, 28 Apr 2023 05:04:42 +0000
From:   Fangrui Song <maskray@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, Bill Wendling <morbo@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Fangrui Song <maskray@...gle.com>
Subject: [PATCH] arm64: lds: move .got section out of .text

Currently, the .got section is placed within the output section .text.
However, when .got is non-empty, the SHF_WRITE flag is set when linked
by lld. GNU ld recognizes .text as a special section and ignores the
SHF_WRITE flag. By renaming .text, we can also get the SHF_WRITE flag.

Conventionally, the .got section is placed just before .got.plt (which
should be empty and omitted in the kernel). Therefore, we move the .got
section to a conventional location (between .text and .data) and remove
the unneeded `. = ALIGN(16)`.

Signed-off-by: Fangrui Song <maskray@...gle.com>
---
 arch/arm64/kernel/vmlinux.lds.S | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index b9202c2ee18e..2bcb3b30db41 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -181,18 +181,8 @@ SECTIONS
 			KPROBES_TEXT
 			HYPERVISOR_TEXT
 			*(.gnu.warning)
-		. = ALIGN(16);
-		*(.got)			/* Global offset table		*/
 	}
 
-	/*
-	 * Make sure that the .got.plt is either completely empty or it
-	 * contains only the lazy dispatch entries.
-	 */
-	.got.plt : { *(.got.plt) }
-	ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
-	       "Unexpected GOT/PLT entries detected!")
-
 	. = ALIGN(SEGMENT_ALIGN);
 	_etext = .;			/* End of text section */
 
@@ -247,6 +237,16 @@ SECTIONS
 
 	. = ALIGN(SEGMENT_ALIGN);
 	__inittext_end = .;
+
+	.got : { *(.got) }
+	/*
+	 * Make sure that the .got.plt is either completely empty or it
+	 * contains only the lazy dispatch entries.
+	 */
+	.got.plt : { *(.got.plt) }
+	ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
+	       "Unexpected GOT/PLT entries detected!")
+
 	__initdata_begin = .;
 
 	init_idmap_pg_dir = .;
-- 
2.40.1.495.gc816e09b53d-goog