linux-kernel - [PATCH v2 2/2] arch/x86: Drop unneeded linker script discard of .eh

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Message-Id: <20200224232129.597160-3-nivedita@alum.mit.edu>
Date:   Mon, 24 Feb 2020 18:21:29 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Michael Matz <matz@...e.de>, Fangrui Song <maskray@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 2/2] arch/x86: Drop unneeded linker script discard of .eh_frame

Now that we don't generate .eh_frame sections for the files in setup.elf
and realmode.elf, the linker scripts don't need the /DISCARD/ any more.

Remove the one in the main kernel linker script as well, since there are
no .eh_frame sections already, and fix up a comment referencing .eh_frame.

Update the comment in asm/dwarf2.h referring to .eh_frame so it continues
to make sense, as well as being more specific.

Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 arch/x86/boot/compressed/vmlinux.lds.S | 5 -----
 arch/x86/boot/setup.ld                 | 1 -
 arch/x86/include/asm/dwarf2.h          | 4 ++--
 arch/x86/kernel/vmlinux.lds.S          | 7 ++-----
 arch/x86/realmode/rm/realmode.lds.S    | 1 -
 5 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 469dcf800a2c..508cfa6828c5 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -73,9 +73,4 @@ SECTIONS
 #endif
 	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
 	_end = .;
-
-	/* Discard .eh_frame to save some space */
-	/DISCARD/ : {
-		*(.eh_frame)
-	}
 }
diff --git a/arch/x86/boot/setup.ld b/arch/x86/boot/setup.ld
index 3da1c37c6dd5..24c95522f231 100644
--- a/arch/x86/boot/setup.ld
+++ b/arch/x86/boot/setup.ld
@@ -52,7 +52,6 @@ SECTIONS
 	_end = .;
 
 	/DISCARD/	: {
-		*(.eh_frame)
 		*(.note*)
 	}
 
diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
index ae391f609840..f71a0cce9373 100644
--- a/arch/x86/include/asm/dwarf2.h
+++ b/arch/x86/include/asm/dwarf2.h
@@ -42,8 +42,8 @@
 	 * Emit CFI data in .debug_frame sections, not .eh_frame sections.
 	 * The latter we currently just discard since we don't do DWARF
 	 * unwinding at runtime.  So only the offline DWARF information is
-	 * useful to anyone.  Note we should not use this directive if
-	 * vmlinux.lds.S gets changed so it doesn't discard .eh_frame.
+	 * useful to anyone.  Note we should not use this directive if we
+	 * ever decide to enable DWARF unwinding at runtime.
 	 */
 	.cfi_sections .debug_frame
 #else
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e3296aa028fe..5cab3a29adcb 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -313,8 +313,8 @@ SECTIONS
 
 	. = ALIGN(8);
 	/*
-	 * .exit.text is discard at runtime, not link time, to deal with
-	 *  references from .altinstructions and .eh_frame
+	 * .exit.text is discarded at runtime, not link time, to deal with
+	 *  references from .altinstructions
 	 */
 	.exit.text : AT(ADDR(.exit.text) - LOAD_OFFSET) {
 		EXIT_TEXT
@@ -412,9 +412,6 @@ SECTIONS
 	DWARF_DEBUG
 
 	DISCARDS
-	/DISCARD/ : {
-		*(.eh_frame)
-	}
 }
 
 
diff --git a/arch/x86/realmode/rm/realmode.lds.S b/arch/x86/realmode/rm/realmode.lds.S
index 64d135d1ee63..63aa51875ba0 100644
--- a/arch/x86/realmode/rm/realmode.lds.S
+++ b/arch/x86/realmode/rm/realmode.lds.S
@@ -71,7 +71,6 @@ SECTIONS
 	/DISCARD/ : {
 		*(.note*)
 		*(.debug*)
-		*(.eh_frame*)
 	}
 
 #include "pasyms.h"
-- 
2.24.1