x86/vmlinux: Drop unneeded linker script discard of .eh_frame

Now that .eh_frame sections for the files in setup.elf and realmode.elf
are not generated anymore, the linker scripts don't need the special
output section name /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.

 [ bp: Touch up commit message. ]
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://lkml.kernel.org/r/20200224232129.597160-3-nivedita@alum.mit.edu

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)
-	}
 }

arch/x86/boot/setup.ld

@@ -52,7 +52,6 @@ SECTIONS
 	_end = .;
 
 	/DISCARD/	: {
-		*(.eh_frame)
 		*(.note*)
 	}
 

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

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)
-	}
 }
 
 

arch/x86/realmode/rm/realmode.lds.S

@@ -71,7 +71,6 @@ SECTIONS
 	/DISCARD/ : {
 		*(.note*)
 		*(.debug*)
-		*(.eh_frame*)
 	}
 
 #include "pasyms.h"