From b14784e7883390c20ed3ff904892255404a5914b Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@nbd.name>
Date: Fri, 7 Jul 2017 17:05:53 +0200
Subject: add an optional config option for stripping all unnecessary symbol exports from the kernel image

lede-commit: bb5a40c64b7c4f4848509fa0a6625055fc9e66cc
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 include/asm-generic/vmlinux.lds.h | 18 +++++++++++++++---
 include/linux/export.h            |  9 ++++++++-
 scripts/Makefile.build            |  2 +-
 3 files changed, 24 insertions(+), 5 deletions(-)

--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -81,6 +81,16 @@
 #define RO_EXCEPTION_TABLE
 #endif
 
+#ifndef SYMTAB_KEEP
+#define SYMTAB_KEEP KEEP(*(SORT(___ksymtab+*)))
+#define SYMTAB_KEEP_GPL KEEP(*(SORT(___ksymtab_gpl+*)))
+#endif
+
+#ifndef SYMTAB_DISCARD
+#define SYMTAB_DISCARD
+#define SYMTAB_DISCARD_GPL
+#endif
+
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)
 
@@ -512,14 +522,14 @@
 	/* Kernel symbol table: Normal symbols */			\
 	__ksymtab         : AT(ADDR(__ksymtab) - LOAD_OFFSET) {		\
 		__start___ksymtab = .;					\
-		KEEP(*(SORT(___ksymtab+*)))				\
+		SYMTAB_KEEP						\
 		__stop___ksymtab = .;					\
 	}								\
 									\
 	/* Kernel symbol table: GPL-only symbols */			\
 	__ksymtab_gpl     : AT(ADDR(__ksymtab_gpl) - LOAD_OFFSET) {	\
 		__start___ksymtab_gpl = .;				\
-		KEEP(*(SORT(___ksymtab_gpl+*)))				\
+		SYMTAB_KEEP_GPL						\
 		__stop___ksymtab_gpl = .;				\
 	}								\
 									\
@@ -539,7 +549,7 @@
 									\
 	/* Kernel symbol table: strings */				\
         __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) {	\
-		*(__ksymtab_strings)					\
+		*(__ksymtab_strings+*)					\
 	}								\
 									\
 	/* __*init sections */						\
@@ -1048,6 +1058,8 @@
 #define COMMON_DISCARDS							\
 	SANITIZER_DISCARDS						\
 	PATCHABLE_DISCARDS						\
+	SYMTAB_DISCARD							\
+	SYMTAB_DISCARD_GPL						\
 	*(.discard)							\
 	*(.discard.*)							\
 	*(.modinfo)							\
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -72,6 +72,12 @@ struct kernel_symbol {
 
 #else
 
+#ifdef MODULE
+#define __EXPORT_SUFFIX(sym)
+#else
+#define __EXPORT_SUFFIX(sym) "+" #sym
+#endif
+
 /*
  * For every exported symbol, do the following:
  *
@@ -87,7 +93,7 @@ struct kernel_symbol {
 	extern typeof(sym) sym;							\
 	extern const char __kstrtab_##sym[];					\
 	extern const char __kstrtabns_##sym[];					\
-	asm("	.section \"__ksymtab_strings\",\"aMS\",%progbits,1	\n"	\
+	asm("	.section \"__ksymtab_strings" __EXPORT_SUFFIX(sym) "\",\"aMS\",%progbits,1	\n"	\
 	    "__kstrtab_" #sym ":					\n"	\
 	    "	.asciz 	\"" #sym "\"					\n"	\
 	    "__kstrtabns_" #sym ":					\n"	\
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -31,6 +31,12 @@
 #endif
 .endm
 
+#ifdef MODULE
+#define __EXPORT_SUFFIX(name)
+#else
+#define __EXPORT_SUFFIX(name) + #name
+#endif
+
 /*
  * note on .section use: we specify progbits since usage of the "M" (SHF_MERGE)
  * section flag requires it. Use '%progbits' instead of '@progbits' since the
@@ -44,7 +50,7 @@
 __ksymtab_\name:
 	__put \val, __kstrtab_\name
 	.previous
-	.section __ksymtab_strings,"aMS",%progbits,1
+	.section __ksymtab_strings __EXPORT_SUFFIX(name),"aMS",%progbits,1
 __kstrtab_\name:
 	.asciz "\name"
 	.previous
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -388,7 +388,7 @@ targets += $(real-dtb-y) $(lib-y) $(alwa
 # Linker scripts preprocessor (.lds.S -> .lds)
 # ---------------------------------------------------------------------------
 quiet_cmd_cpp_lds_S = LDS     $@
-      cmd_cpp_lds_S = $(CPP) $(cpp_flags) -P -U$(ARCH) \
+      cmd_cpp_lds_S = $(CPP) $(EXTRA_LDSFLAGS) $(cpp_flags) -P -U$(ARCH) \
 	                     -D__ASSEMBLY__ -DLINKER_SCRIPT -o $@ $<
 
 $(obj)/%.lds: $(src)/%.lds.S FORCE
