[PATCH] GP-REL data support

The attached patch makes it possible to support gp-rel addressing for small
variables.  Since the FR-V cpu's have fixed-length instructions and plenty of
general-purpose registers, one register is nominated as a base for the small
data area.  This makes it possible to use single-insn accesses to access
global and static variables instead of having to use multiple instructions.

This, however, causes problems with small variables used to pinpoint the
beginning and end of sections.  The compiler assumes it can use gp-rel
addressing for these, but the linker then complains because the displacement
is out of range.

By declaring certain variables as arrays or by forcing them into named
sections, the compiler is persuaded to access them as if they can be outside
the displacement range.  Declaring the variables as "const void" type also
works.
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/char/tty_io.c

@@ -2903,8 +2903,8 @@ void __init console_init(void)
 	   So I haven't moved it. dwmw2 */
         rs_360_init();
 #endif
-	call = &__con_initcall_start;
-	while (call < &__con_initcall_end) {
+	call = __con_initcall_start;
+	while (call < __con_initcall_end) {
 		(*call)();
 		call++;
 	}

fs/proc/proc_misc.c

@@ -256,7 +256,6 @@ static struct file_operations fragmentation_file_operations = {
 static int version_read_proc(char *page, char **start, off_t off,
 				 int count, int *eof, void *data)
 {
-	extern char *linux_banner;
 	int len;
 
 	strcpy(page, linux_banner);

include/asm-generic/sections.h

@@ -8,5 +8,6 @@ extern char _data[], _sdata[], _edata[];
 extern char __bss_start[], __bss_stop[];
 extern char __init_begin[], __init_end[];
 extern char _sinittext[], _einittext[];
+extern char _end[];
 
 #endif /* _ASM_GENERIC_SECTIONS_H_ */

include/asm-ia64/sections.h

@@ -17,7 +17,6 @@ extern char __start_gate_vtop_patchlist[], __end_gate_vtop_patchlist[];
 extern char __start_gate_fsyscall_patchlist[], __end_gate_fsyscall_patchlist[];
 extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_bubble_down_patchlist[];
 extern char __start_unwind[], __end_unwind[];
-extern char _end[];		/* end of kernel image */
 
 #endif /* _ASM_IA64_SECTIONS_H */
 

include/asm-ppc/sections.h

@@ -4,8 +4,6 @@
 
 #include <asm-generic/sections.h>
 
-extern char _end[];
-
 #define __pmac __attribute__ ((__section__ (".pmac.text")))
 #define __pmacdata __attribute__ ((__section__ (".pmac.data")))
 #define __pmacfunc(__argpmac) \

include/asm-sparc64/sections.h

@@ -4,6 +4,6 @@
 /* nothing to see, move along */
 #include <asm-generic/sections.h>
 
-extern char _end[], _start[];
+extern char _start[];
 
 #endif

include/linux/init.h

@@ -64,8 +64,8 @@
 typedef int (*initcall_t)(void);
 typedef void (*exitcall_t)(void);
 
-extern initcall_t __con_initcall_start, __con_initcall_end;
-extern initcall_t __security_initcall_start, __security_initcall_end;
+extern initcall_t __con_initcall_start[], __con_initcall_end[];
+extern initcall_t __security_initcall_start[], __security_initcall_end[];
 
 /* Defined in init/main.c */
 extern char saved_command_line[];

include/linux/jiffies.h

@@ -70,13 +70,19 @@
 /* a value TUSEC for TICK_USEC (can be set bij adjtimex)		*/
 #define TICK_USEC_TO_NSEC(TUSEC) (SH_DIV (TUSEC * USER_HZ * 1000, ACTHZ, 8))
 
+/* some arch's have a small-data section that can be accessed register-relative
+ * but that can only take up to, say, 4-byte variables. jiffies being part of
+ * an 8-byte variable may not be correctly accessed unless we force the issue
+ */
+#define __jiffy_data  __attribute__((section(".data")))
+
 /*
  * The 64-bit value is not volatile - you MUST NOT read it
  * without sampling the sequence number in xtime_lock.
  * get_jiffies_64() will do this for you as appropriate.
  */
-extern u64 jiffies_64;
-extern unsigned long volatile jiffies;
+extern u64 __jiffy_data jiffies_64;
+extern unsigned long volatile __jiffy_data jiffies;
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void);

include/linux/kernel.h

@@ -16,6 +16,8 @@
 #include <asm/byteorder.h>
 #include <asm/bug.h>
 
+extern const char linux_banner[];
+
 #define INT_MAX		((int)(~0U>>1))
 #define INT_MIN		(-INT_MAX - 1)
 #define UINT_MAX	(~0U)

init/initramfs.c

@@ -460,15 +460,15 @@ char * __init unpack_to_rootfs(char *buf, unsigned len, int check_only)
 	return message;
 }
 
-extern char __initramfs_start, __initramfs_end;
+extern char __initramfs_start[], __initramfs_end[];
 #ifdef CONFIG_BLK_DEV_INITRD
 #include <linux/initrd.h>
 #endif
 
 void __init populate_rootfs(void)
 {
-	char *err = unpack_to_rootfs(&__initramfs_start,
-			 &__initramfs_end - &__initramfs_start, 0);
+	char *err = unpack_to_rootfs(__initramfs_start,
+			 __initramfs_end - __initramfs_start, 0);
 	if (err)
 		panic(err);
 #ifdef CONFIG_BLK_DEV_INITRD

init/main.c

@@ -75,8 +75,6 @@
 #error Sorry, your GCC is too old. It builds incorrect kernels.
 #endif
 
-extern char *linux_banner;
-
 static int init(void *);
 
 extern void init_IRQ(void);
@@ -157,12 +155,13 @@ static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
 char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
 static const char *panic_later, *panic_param;
 
+extern struct obs_kernel_param __setup_start[], __setup_end[];
+
 static int __init obsolete_checksetup(char *line)
 {
 	struct obs_kernel_param *p;
-	extern struct obs_kernel_param __setup_start, __setup_end;
 
-	p = &__setup_start;
+	p = __setup_start;
 	do {
 		int n = strlen(p->str);
 		if (!strncmp(line, p->str, n)) {
@@ -179,7 +178,7 @@ static int __init obsolete_checksetup(char *line)
 				return 1;
 		}
 		p++;
-	} while (p < &__setup_end);
+	} while (p < __setup_end);
 	return 0;
 }
 
@@ -453,9 +452,8 @@ static void noinline rest_init(void)
 static int __init do_early_param(char *param, char *val)
 {
 	struct obs_kernel_param *p;
-	extern struct obs_kernel_param __setup_start, __setup_end;
 
-	for (p = &__setup_start; p < &__setup_end; p++) {
+	for (p = __setup_start; p < __setup_end; p++) {
 		if (p->early && strcmp(param, p->str) == 0) {
 			if (p->setup_func(val) != 0)
 				printk(KERN_WARNING
@@ -592,14 +590,14 @@ __setup("initcall_debug", initcall_debug_setup);
 
 struct task_struct *child_reaper = &init_task;
 
-extern initcall_t __initcall_start, __initcall_end;
+extern initcall_t __initcall_start[], __initcall_end[];
 
 static void __init do_initcalls(void)
 {
 	initcall_t *call;
 	int count = preempt_count();
 
-	for (call = &__initcall_start; call < &__initcall_end; call++) {
+	for (call = __initcall_start; call < __initcall_end; call++) {
 		char *msg;
 
 		if (initcall_debug) {

init/version.c

@@ -28,6 +28,6 @@ struct new_utsname system_utsname = {
 
 EXPORT_SYMBOL(system_utsname);
 
-const char *linux_banner = 
+const char linux_banner[] =
 	"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
 	LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";

kernel/kallsyms.c

@@ -20,6 +20,8 @@
 #include <linux/proc_fs.h>
 #include <linux/mm.h>
 
+#include <asm/sections.h>
+
 #ifdef CONFIG_KALLSYMS_ALL
 #define all_var 1
 #else
@@ -28,7 +30,7 @@
 
 /* These will be re-linked against their real values during the second link stage */
 extern unsigned long kallsyms_addresses[] __attribute__((weak));
-extern unsigned long kallsyms_num_syms __attribute__((weak));
+extern unsigned long kallsyms_num_syms __attribute__((weak,section("data")));
 extern u8 kallsyms_names[] __attribute__((weak));
 
 extern u8 kallsyms_token_table[] __attribute__((weak));
@@ -36,9 +38,6 @@ extern u16 kallsyms_token_index[] __attribute__((weak));
 
 extern unsigned long kallsyms_markers[] __attribute__((weak));
 
-/* Defined by the linker script. */
-extern char _stext[], _etext[], _sinittext[], _einittext[], _end[];
-
 static inline int is_kernel_inittext(unsigned long addr)
 {
 	if (addr >= (unsigned long)_sinittext

kernel/power/swsusp.c

@@ -72,7 +72,7 @@
 #include "power.h"
 
 /* References to section boundaries */
-extern char __nosave_begin, __nosave_end;
+extern const void __nosave_begin, __nosave_end;
 
 /* Variables to be preserved over suspend */
 static int pagedir_order_check;

security/security.c

@@ -38,8 +38,8 @@ static inline int verify(struct security_operations *ops)
 static void __init do_security_initcalls(void)
 {
 	initcall_t *call;
-	call = &__security_initcall_start;
-	while (call < &__security_initcall_end) {
+	call = __security_initcall_start;
+	while (call < __security_initcall_end) {
 		(*call) ();
 		call++;
 	}