Re: [PATCH] kbuild: protect compiled-in dtb from dead data elimination

[Nicholas Piggin]

On Wed, 26 Oct 2016 10:47:43 +0200
Marcin Nowakowski <marcin.nowakowski@xxxxxxxxxx> wrote:

> DTBs are compiled into byte arrays that are placed inside
> .dtb.init.rodata section. As they are never referenced directly from the
> code, they get removed during dead data elimination and we end up with
> __dtb_start == __dtb_end.

Thanks, I got a bunch of patches from Paul for similar, so I
went through it and we've actually got a lot of tables we should
probably protect with KEEP(). For reference this is what I have
on top of Paul's patches. I'll send them up to kbuild after we
get this CRC build issue dealt with.

I'm glad you guys are finding it useful.

Thanks,
Nick



From: Nicholas Piggin <npiggin@xxxxxxxxx>
Date: Tue, 25 Oct 2016 20:42:42 +1100
Subject: [PATCH] kbuild: dead code elimination keep various other tables

This should get a little bit less painful as things eventually move
to generic linker table helper macros, but for now be liberal in
keeping data tables.

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
 include/asm-generic/vmlinux.lds.h | 32 ++++++++++++++++----------------
 1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index abe79e3..1cac167 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -184,7 +184,7 @@
 #define ACPI_PROBE_TABLE(name)						\
 	. = ALIGN(8);							\
 	VMLINUX_SYMBOL(__##name##_acpi_probe_table) = .;		\
-	*(__##name##_acpi_probe_table)					\
+	KEEP(*(__##name##_acpi_probe_table))				\
 	VMLINUX_SYMBOL(__##name##_acpi_probe_table_end) = .;
 #else
 #define ACPI_PROBE_TABLE(name)
@@ -193,7 +193,7 @@
 #define KERNEL_DTB()							\
 	STRUCT_ALIGN();							\
 	VMLINUX_SYMBOL(__dtb_start) = .;				\
-	*(.dtb.init.rodata)						\
+	KEEP(*(.dtb.init.rodata))					\
 	VMLINUX_SYMBOL(__dtb_end) = .;
 
 /*
@@ -214,11 +214,11 @@
 	/* implement dynamic printk debug */				\
 	. = ALIGN(8);                                                   \
 	VMLINUX_SYMBOL(__start___jump_table) = .;                       \
-	*(__jump_table)                                                 \
+	KEEP(*(__jump_table))                                           \
 	VMLINUX_SYMBOL(__stop___jump_table) = .;                        \
 	. = ALIGN(8);							\
 	VMLINUX_SYMBOL(__start___verbose) = .;                          \
-	*(__verbose)                                                    \
+	KEEP(*(__verbose))                                              \
 	VMLINUX_SYMBOL(__stop___verbose) = .;				\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
@@ -271,10 +271,10 @@
 		VMLINUX_SYMBOL(__start_rodata) = .;			\
 		*(.rodata) *(.rodata.*)					\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
-		*(__vermagic)		/* Kernel version magic */	\
+		KEEP(*(__vermagic))	/* Kernel version magic */	\
 		. = ALIGN(8);						\
 		VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .;		\
-		*(__tracepoints_ptrs)	/* Tracepoints: pointer array */\
+		KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \
 		VMLINUX_SYMBOL(__stop___tracepoints_ptrs) = .;		\
 		*(__tracepoints_strings)/* Tracepoints: strings */	\
 	}								\
@@ -316,7 +316,7 @@
 	/* Built-in firmware blobs */					\
 	.builtin_fw        : AT(ADDR(.builtin_fw) - LOAD_OFFSET) {	\
 		VMLINUX_SYMBOL(__start_builtin_fw) = .;			\
-		*(.builtin_fw)						\
+		KEEP(*(.builtin_fw))					\
 		VMLINUX_SYMBOL(__end_builtin_fw) = .;			\
 	}								\
 									\
@@ -394,7 +394,7 @@
 									\
 	/* Kernel symbol table: strings */				\
         __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) {	\
-		KEEP(*(__ksymtab_strings))				\
+		*(__ksymtab_strings)					\
 	}								\
 									\
 	/* __*init sections */						\
@@ -407,14 +407,14 @@
 	/* Built-in module parameters. */				\
 	__param : AT(ADDR(__param) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___param) = .;			\
-		*(__param)						\
+		KEEP(*(__param))					\
 		VMLINUX_SYMBOL(__stop___param) = .;			\
 	}								\
 									\
 	/* Built-in module versions. */					\
 	__modver : AT(ADDR(__modver) - LOAD_OFFSET) {			\
 		VMLINUX_SYMBOL(__start___modver) = .;			\
-		*(__modver)						\
+		KEEP(*(__modver))					\
 		VMLINUX_SYMBOL(__stop___modver) = .;			\
 		. = ALIGN((align));					\
 		VMLINUX_SYMBOL(__end_rodata) = .;			\
@@ -517,7 +517,7 @@
 	. = ALIGN(align);						\
 	__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {		\
 		VMLINUX_SYMBOL(__start___ex_table) = .;			\
-		*(__ex_table)						\
+		KEEP(*(__ex_table))					\
 		VMLINUX_SYMBOL(__stop___ex_table) = .;			\
 	}
 
@@ -533,9 +533,9 @@
 #ifdef CONFIG_CONSTRUCTORS
 #define KERNEL_CTORS()	. = ALIGN(8);			   \
 			VMLINUX_SYMBOL(__ctors_start) = .; \
-			*(.ctors)			   \
-			*(SORT(.init_array.*))		   \
-			*(.init_array)			   \
+			KEEP(*(.ctors))			   \
+			KEEP(*(SORT(.init_array.*)))	   \
+			KEEP(*(.init_array))		   \
 			VMLINUX_SYMBOL(__ctors_end) = .;
 #else
 #define KERNEL_CTORS()
@@ -659,7 +659,7 @@
 	. = ALIGN(8);							\
 	__bug_table : AT(ADDR(__bug_table) - LOAD_OFFSET) {		\
 		VMLINUX_SYMBOL(__start___bug_table) = .;		\
-		*(__bug_table)						\
+		KEEP(*(__bug_table))					\
 		VMLINUX_SYMBOL(__stop___bug_table) = .;			\
 	}
 #else
@@ -671,7 +671,7 @@
 	. = ALIGN(4);							\
 	.tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) {		\
 		VMLINUX_SYMBOL(__tracedata_start) = .;			\
-		*(.tracedata)						\
+		KEEP(*(.tracedata))					\
 		VMLINUX_SYMBOL(__tracedata_end) = .;			\
 	}
 #else
-- 
2.9.3