arm/build: Explicitly keep .ARM.attributes sections

In preparation for adding --orphan-handling=warn, explicitly keep the
.ARM.attributes section (at address 0[1]) by expanding the existing
ELF_DETAILS macro into ARM_DETAILS.

[1] https://reviews.llvm.org/D85867Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Fangrui Song <maskray@google.com>
Cc: Russell King <linux@armlinux.org.uk>
Link: https://lore.kernel.org/lkml/CAKwvOdk-racgq5pxsoGS6Vtifbtrk5fmkmnoLxrQMaOvV0nPWw@mail.gmail.com/
Link: https://lore.kernel.org/r/20200821194310.3089815-17-keescook@chromium.org

arch/arm/include/asm/vmlinux.lds.h

@@ -52,6 +52,10 @@
 		ARM_MMU_DISCARD(*(__ex_table))				\
 		COMMON_DISCARDS
 
+#define ARM_DETAILS							\
+		ELF_DETAILS						\
+		.ARM.attributes 0 : { *(.ARM.attributes) }
+
 #define ARM_STUBS_TEXT							\
 		*(.gnu.warning)						\
 		*(.glue_7)						\

arch/arm/kernel/vmlinux-xip.lds.S

@@ -150,7 +150,7 @@ SECTIONS
 	_end = .;
 
 	STABS_DEBUG
-	ELF_DETAILS
+	ARM_DETAILS
 }
 
 /*

arch/arm/kernel/vmlinux.lds.S

@@ -149,7 +149,7 @@ SECTIONS
 	_end = .;
 
 	STABS_DEBUG
-	ELF_DETAILS
+	ARM_DETAILS
 }
 
 #ifdef CONFIG_STRICT_KERNEL_RWX