[PATCH v2 0/4] LD_DEAD_CODE_DATA_ELIMINATION fixes and enabling for powerpc

@@ -64,15 +64,24 @@
  * generates .data.identifier sections, which need to be pulled in with
  * .data. We don't want to pull in .data..other sections, which Linux
  * has defined. Same for text and bss.
+ *
+ * RODATA_MAIN is not used because existing code already defines .rodata.x
+ * sections to be brought in with rodata.
  */
 #ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
 #define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
 #define DATA_MAIN .data .data.[0-9a-zA-Z_]*
+#define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]*
+#define RODATA_MAIN .rodata .rodata.[0-9a-zA-Z_]*
 #define BSS_MAIN .bss .bss.[0-9a-zA-Z_]*
+#define SBSS_MAIN .sbss .sbss.[0-9a-zA-Z_]*
 #else
 #define TEXT_MAIN .text
 #define DATA_MAIN .data
+#define SDATA_MAIN .sdata
+#define RODATA_MAIN .rodata
 #define BSS_MAIN .bss
+#define SBSS_MAIN .sbss
 #endif
 
 /*

@@ -105,7 +114,7 @@
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 #define MCOUNT_REC()	. = ALIGN(8);				\
 			VMLINUX_SYMBOL(__start_mcount_loc) = .; \
-			*(__mcount_loc)				\
+			KEEP(*(__mcount_loc))			\
 			VMLINUX_SYMBOL(__stop_mcount_loc) = .;
 #else
 #define MCOUNT_REC()

@@ -113,7 +122,7 @@
 
 #ifdef CONFIG_TRACE_BRANCH_PROFILING
 #define LIKELY_PROFILE()	VMLINUX_SYMBOL(__start_annotated_branch_profile) = .; \
-				*(_ftrace_annotated_branch)			      \
+				KEEP(*(_ftrace_annotated_branch))		      \
 				VMLINUX_SYMBOL(__stop_annotated_branch_profile) = .;
 #else
 #define LIKELY_PROFILE()

@@ -121,7 +130,7 @@
 
 #ifdef CONFIG_PROFILE_ALL_BRANCHES
 #define BRANCH_PROFILE()	VMLINUX_SYMBOL(__start_branch_profile) = .;   \
-				*(_ftrace_branch)			      \
+				KEEP(*(_ftrace_branch))			      \
 				VMLINUX_SYMBOL(__stop_branch_profile) = .;
 #else
 #define BRANCH_PROFILE()

@@ -238,8 +247,8 @@
 	*(DATA_MAIN)							\
 	*(.ref.data)							\
 	*(.data..shared_aligned) /* percpu related */			\
-	MEM_KEEP(init.data)						\
-	MEM_KEEP(exit.data)						\
+	MEM_KEEP(init.data*)						\
+	MEM_KEEP(exit.data*)						\
 	*(.data.unlikely)						\
 	VMLINUX_SYMBOL(__start_once) = .;				\
 	*(.data.once)							\

@@ -289,8 +298,8 @@
 	VMLINUX_SYMBOL(__start_init_task) = .;				\
 	VMLINUX_SYMBOL(init_thread_union) = .;				\
 	VMLINUX_SYMBOL(init_stack) = .;					\
-	*(.data..init_task)						\
-	*(.data..init_thread_info)					\
+	KEEP(*(.data..init_task))					\
+	KEEP(*(.data..init_thread_info))				\
 	. = VMLINUX_SYMBOL(__start_init_task) + THREAD_SIZE;		\
 	VMLINUX_SYMBOL(__end_init_task) = .;
 

@@ -487,8 +496,8 @@
 		*(.text.hot TEXT_MAIN .text.fixup .text.unlikely)	\
 		*(.text..refcount)					\
 		*(.ref.text)						\
-	MEM_KEEP(init.text)						\
-	MEM_KEEP(exit.text)						\
+	MEM_KEEP(init.text*)						\
+	MEM_KEEP(exit.text*)						\
 
 
 /* sched.text is aling to function alignment to secure we have same

@@ -538,7 +547,7 @@
 		VMLINUX_SYMBOL(__softirqentry_text_end) = .;
 
 /* Section used for early init (in .S files) */
-#define HEAD_TEXT  *(.head.text)
+#define HEAD_TEXT  KEEP(*(.head.text))
 
 #define HEAD_TEXT_SECTION							\
 	.head.text : AT(ADDR(.head.text) - LOAD_OFFSET) {		\

@@ -579,11 +588,11 @@
 /* init and exit section handling */
 #define INIT_DATA							\
 	KEEP(*(SORT(___kentry+*)))					\
-	*(.init.data)							\
-	MEM_DISCARD(init.data)						\
+	*(.init.data init.data.*)					\
+	MEM_DISCARD(init.data*)						\
 	KERNEL_CTORS()							\
 	MCOUNT_REC()							\
-	*(.init.rodata)							\
+	*(.init.rodata .init.rodata.*)					\
 	FTRACE_EVENTS()							\
 	TRACE_SYSCALLS()						\
 	KPROBE_BLACKLIST()						\

@@ -602,16 +611,16 @@
 	EARLYCON_TABLE()
 
 #define INIT_TEXT							\
-	*(.init.text)							\
+	*(.init.text .init.text.*)					\
 	*(.text.startup)						\
-	MEM_DISCARD(init.text)
+	MEM_DISCARD(init.text*)
 
 #define EXIT_DATA							\
-	*(.exit.data)							\
+	*(.exit.data .exit.data.*)					\
 	*(.fini_array)							\
 	*(.dtors)							\
-	MEM_DISCARD(exit.data)						\
-	MEM_DISCARD(exit.rodata)
+	MEM_DISCARD(exit.data*)						\
+	MEM_DISCARD(exit.rodata*)
 
 #define EXIT_TEXT							\
 	*(.exit.text)							\

@@ -629,7 +638,7 @@
 	. = ALIGN(sbss_align);						\
 	.sbss : AT(ADDR(.sbss) - LOAD_OFFSET) {				\
 		*(.dynsbss)						\
-		*(.sbss)						\
+		*(SBSS_MAIN)						\
 		*(.scommon)						\
 	}
 

@@ -754,7 +763,7 @@
 #define NOTES								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start_notes) = .;			\
-		*(.note.*)						\
+		KEEP(*(.note.*))					\
 		VMLINUX_SYMBOL(__stop_notes) = .;			\
 	}
 

@@ -799,8 +799,8 @@ KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
 endif
 
 ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
-KBUILD_CFLAGS	+= $(call cc-option,-ffunction-sections,)
-KBUILD_CFLAGS	+= $(call cc-option,-fdata-sections,)
+KBUILD_CFLAGS_KERNEL	+= $(call cc-option,-ffunction-sections,)
+KBUILD_CFLAGS_KERNEL	+= $(call cc-option,-fdata-sections,)
 endif
 
 # arch Makefile may override CC so keep this after arch Makefile is included

@@ -596,21 +596,6 @@ config CC_STACKPROTECTOR_AUTO
 
 endchoice
 
-config LD_DEAD_CODE_DATA_ELIMINATION
-	bool
-	help
-	  Select this if the architecture wants to do dead code and
-	  data elimination with the linker by compiling with
-	  -ffunction-sections -fdata-sections and linking with
-	  --gc-sections.
-
-	  This requires that the arch annotates or otherwise protects
-	  its external entry points from being discarded. Linker scripts
-	  must also merge .text.*, .data.*, and .bss.* correctly into
-	  output sections. Care must be taken not to pull in unrelated
-	  sections (e.g., '.text.init'). Typically '.' in section names
-	  is used to distinguish them from label names / C identifiers.
-
 config HAVE_ARCH_WITHIN_STACK_FRAMES
 	bool
 	help

@@ -1038,6 +1038,33 @@ config CC_OPTIMIZE_FOR_SIZE
 
 endchoice
 
+config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
+	bool
+	help
+	  This requires that the arch annotates or otherwise protects
+	  its external entry points from being discarded. Linker scripts
+	  must also merge .text.*, .data.*, and .bss.* correctly into
+	  output sections. Care must be taken not to pull in unrelated
+	  sections (e.g., '.text.init'). Typically '.' in section names
+	  is used to distinguish them from label names / C identifiers.
+
+config LD_DEAD_CODE_DATA_ELIMINATION
+	bool "Dead code and data elimination (EXPERIMENTAL)"
+	depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
+	depends on EXPERT
+	help
+	  Select this if the architecture wants to do dead code and
+	  data elimination with the linker by compiling with
+	  -ffunction-sections -fdata-sections, and linking with
+	  --gc-sections.
+
+	  This can reduce on disk and in-memory size of the kernel
+	  code and static data, particularly for small configs and
+	  on small systems. This has the possibility of introducing
+	  silently broken kernel if the required annotations are not
+	  present. This option is not well tested yet, so use at your
+	  own risk.
+
 config SYSCTL
 	bool
 

@@ -205,6 +205,7 @@ config PPC
 	select HAVE_KPROBES
 	select HAVE_KPROBES_ON_FTRACE
 	select HAVE_KRETPROBES
+	select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
 	select HAVE_LIVEPATCH			if HAVE_DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_MEMBLOCK
 	select HAVE_MEMBLOCK_NODE_MAP

@@ -89,7 +89,7 @@ SECTIONS
 	 */
 	.text BLOCK(0) : AT(ADDR(.text) - LOAD_OFFSET) {
 #ifdef CONFIG_LD_HEAD_STUB_CATCH
-		*(.linker_stub_catch);
+		KEEP(*(.linker_stub_catch));
 		. = . ;
 #endif
 

@@ -98,7 +98,7 @@ SECTIONS
 		ALIGN_FUNCTION();
 #endif
 		/* careful! __ftr_alt_* sections need to be close to .text */
-		*(.text.hot .text .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
+		*(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
 		SCHED_TEXT
 		CPUIDLE_TEXT
 		LOCK_TEXT

@@ -170,10 +170,10 @@ SECTIONS
 	.init.data : AT(ADDR(.init.data) - LOAD_OFFSET) {
 		INIT_DATA
 		__vtop_table_begin = .;
-		*(.vtop_fixup);
+		KEEP(*(.vtop_fixup));
 		__vtop_table_end = .;
 		__ptov_table_begin = .;
-		*(.ptov_fixup);
+		KEEP(*(.ptov_fixup));
 		__ptov_table_end = .;
 	}
 

@@ -194,26 +194,26 @@ SECTIONS
 	. = ALIGN(8);
 	__ftr_fixup : AT(ADDR(__ftr_fixup) - LOAD_OFFSET) {
 		__start___ftr_fixup = .;
-		*(__ftr_fixup)
+		KEEP(*(__ftr_fixup))
 		__stop___ftr_fixup = .;
 	}
 	. = ALIGN(8);
 	__mmu_ftr_fixup : AT(ADDR(__mmu_ftr_fixup) - LOAD_OFFSET) {
 		__start___mmu_ftr_fixup = .;
-		*(__mmu_ftr_fixup)
+		KEEP(*(__mmu_ftr_fixup))
 		__stop___mmu_ftr_fixup = .;
 	}
 	. = ALIGN(8);
 	__lwsync_fixup : AT(ADDR(__lwsync_fixup) - LOAD_OFFSET) {
 		__start___lwsync_fixup = .;
-		*(__lwsync_fixup)
+		KEEP(*(__lwsync_fixup))
 		__stop___lwsync_fixup = .;
 	}
 #ifdef CONFIG_PPC64
 	. = ALIGN(8);
 	__fw_ftr_fixup : AT(ADDR(__fw_ftr_fixup) - LOAD_OFFSET) {
 		__start___fw_ftr_fixup = .;
-		*(__fw_ftr_fixup)
+		KEEP(*(__fw_ftr_fixup))
 		__stop___fw_ftr_fixup = .;
 	}
 #endif

@@ -226,7 +226,7 @@ SECTIONS
 	. = ALIGN(8);
 	.machine.desc : AT(ADDR(.machine.desc) - LOAD_OFFSET) {
 		__machine_desc_start = . ;
-		*(.machine.desc)
+		KEEP(*(.machine.desc))
 		__machine_desc_end = . ;
 	}
 #ifdef CONFIG_RELOCATABLE

@@ -274,7 +274,7 @@ SECTIONS
 	.data : AT(ADDR(.data) - LOAD_OFFSET) {
 		DATA_DATA
 		*(.data.rel*)
-		*(.sdata)
+		*(SDATA_MAIN)
 		*(.sdata2)
 		*(.got.plt) *(.got)
 		*(.plt)

@@ -289,7 +289,7 @@ SECTIONS
 
 	.opd : AT(ADDR(.opd) - LOAD_OFFSET) {
 		__start_opd = .;
-		*(.opd)
+		KEEP(*(.opd))
 		__end_opd = .;
 	}