s390/exceptions: switch to relative exception table entries

This is the s390 port of 70627654 "x86, extable: Switch to relative
exception table entries".
Reduces the size of our exception tables by 50% on 64 bit builds.

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/include/asm/processor.h

···
 #ifndef __ASM_S390_PROCESSOR_H
 #define __ASM_S390_PROCESSOR_H
 
+#ifndef __ASSEMBLY__
+
 #include <linux/linkage.h>
 #include <linux/irqflags.h>
 #include <asm/cpu.h>
···
 
 #define ARCH_LOW_ADDRESS_LIMIT	0x7fffffffUL
 
-/*
- * Helper macro for exception table entries
- */
-#ifndef CONFIG_64BIT
-#define EX_TABLE(_fault,_target)			\
-	".section __ex_table,\"a\"\n"			\
-	"	.align 4\n"				\
-	"	.long  " #_fault "," #_target "\n"	\
-	".previous\n"
-#else
-#define EX_TABLE(_fault,_target)			\
-	".section __ex_table,\"a\"\n"			\
-	"	.align 8\n"				\
-	"	.quad  " #_fault "," #_target "\n"	\
-	".previous\n"
-#endif
-
 extern int memcpy_real(void *, void *, size_t);
 extern void memcpy_absolute(void *, void *, size_t);
 
···
 	memcpy_absolute(&(dest), &__tmp, sizeof(__tmp));	\
 }
 
-#endif                                 /* __ASM_S390_PROCESSOR_H           */
+/*
+ * Helper macro for exception table entries
+ */
+#define EX_TABLE(_fault, _target)	\
+	".section __ex_table,\"a\"\n"	\
+	".align	4\n"			\
+	".long	(" #_fault ") - .\n"	\
+	".long	(" #_target ") - .\n"	\
+	".previous\n"
+
+#else /* __ASSEMBLY__ */
+
+#define EX_TABLE(_fault, _target)	\
+	.section __ex_table,"a"	;	\
+	.align	4 ;			\
+	.long	(_fault) - . ;		\
+	.long	(_target) - . ;		\
+	.previous
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_S390_PROCESSOR_H */

arch/s390/include/asm/uaccess.h

···
 
 struct exception_table_entry
 {
-        unsigned long insn, fixup;
+	int insn, fixup;
 };
+
+static inline unsigned long extable_insn(const struct exception_table_entry *x)
+{
+	return (unsigned long)&x->insn + x->insn;
+}
+
+static inline unsigned long extable_fixup(const struct exception_table_entry *x)
+{
+	return (unsigned long)&x->fixup + x->fixup;
+}
+
+#define ARCH_HAS_SORT_EXTABLE
+#define ARCH_HAS_SEARCH_EXTABLE
 
 struct uaccess_ops {
 	size_t (*copy_from_user)(size_t, const void __user *, void *);

arch/s390/kernel/early.c

···
 
 static void early_pgm_check_handler(void)
 {
-	unsigned long addr;
 	const struct exception_table_entry *fixup;
+	unsigned long addr;
 
 	addr = S390_lowcore.program_old_psw.addr;
 	fixup = search_exception_tables(addr & PSW_ADDR_INSN);
 	if (!fixup)
 		disabled_wait(0);
-	S390_lowcore.program_old_psw.addr = fixup->fixup | PSW_ADDR_AMODE;
+	S390_lowcore.program_old_psw.addr = extable_fixup(fixup)|PSW_ADDR_AMODE;
 }
 
 static noinline __init void setup_lowcore_early(void)

arch/s390/kernel/entry64.S

···
 
 #include <linux/init.h>
 #include <linux/linkage.h>
+#include <asm/processor.h>
 #include <asm/cache.h>
 #include <asm/errno.h>
 #include <asm/ptrace.h>
···
 .Lhost_id:
 	.quad	0
 
-	.section __ex_table,"a"
-	.quad	sie_loop,sie_fault
-	.previous
+	EX_TABLE(sie_loop,sie_fault)
 #endif
 
 		.section .rodata, "a"

arch/s390/kernel/kprobes.c

···
 		 */
 		entry = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
 		if (entry) {
-			regs->psw.addr = entry->fixup | PSW_ADDR_AMODE;
+			regs->psw.addr = extable_fixup(entry) | PSW_ADDR_AMODE;
 			return 1;
 		}
 

arch/s390/kernel/traps.c

···
                 const struct exception_table_entry *fixup;
                 fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
                 if (fixup)
-                        regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
+			regs->psw.addr = extable_fixup(fixup) | PSW_ADDR_AMODE;
 		else {
 			enum bug_trap_type btt;
 

arch/s390/mm/Makefile

···
 #
 
 obj-y	 := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
-	    page-states.o gup.o
+	    page-states.o gup.o extable.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
 obj-$(CONFIG_DEBUG_SET_MODULE_RONX) += pageattr.o

arch/s390/mm/extable.c

···
+#include <linux/module.h>
+#include <linux/sort.h>
+#include <asm/uaccess.h>
+
+/*
+ * Search one exception table for an entry corresponding to the
+ * given instruction address, and return the address of the entry,
+ * or NULL if none is found.
+ * We use a binary search, and thus we assume that the table is
+ * already sorted.
+ */
+const struct exception_table_entry *
+search_extable(const struct exception_table_entry *first,
+	       const struct exception_table_entry *last,
+	       unsigned long value)
+{
+	const struct exception_table_entry *mid;
+	unsigned long addr;
+
+	while (first <= last) {
+		mid = ((last - first) >> 1) + first;
+		addr = extable_insn(mid);
+		if (addr < value)
+			first = mid + 1;
+		else if (addr > value)
+			last = mid - 1;
+		else
+			return mid;
+	}
+	return NULL;
+}
+
+/*
+ * The exception table needs to be sorted so that the binary
+ * search that we use to find entries in it works properly.
+ * This is used both for the kernel exception table and for
+ * the exception tables of modules that get loaded.
+ *
+ */
+static int cmp_ex(const void *a, const void *b)
+{
+	const struct exception_table_entry *x = a, *y = b;
+
+	/* This compare is only valid after normalization. */
+	return x->insn - y->insn;
+}
+
+void sort_extable(struct exception_table_entry *start,
+		  struct exception_table_entry *finish)
+{
+	struct exception_table_entry *p;
+	int i;
+
+	/* Normalize entries to being relative to the start of the section */
+	for (p = start, i = 0; p < finish; p++, i += 8)
+		p->insn += i;
+	sort(start, finish - start, sizeof(*start), cmp_ex, NULL);
+	/* Denormalize all entries */
+	for (p = start, i = 0; p < finish; p++, i += 8)
+		p->insn -= i;
+}
+
+#ifdef CONFIG_MODULES
+/*
+ * If the exception table is sorted, any referring to the module init
+ * will be at the beginning or the end.
+ */
+void trim_init_extable(struct module *m)
+{
+	/* Trim the beginning */
+	while (m->num_exentries &&
+	       within_module_init(extable_insn(&m->extable[0]), m)) {
+		m->extable++;
+		m->num_exentries--;
+	}
+	/* Trim the end */
+	while (m->num_exentries &&
+	       within_module_init(extable_insn(&m->extable[m->num_exentries-1]), m))
+		m->num_exentries--;
+}
+#endif /* CONFIG_MODULES */

arch/s390/mm/fault.c

···
 	/* Are we prepared to handle this kernel fault?  */
 	fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
 	if (fixup) {
-		regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
+		regs->psw.addr = extable_fixup(fixup) | PSW_ADDR_AMODE;
 		return;
 	}
 

scripts/sortextable.c

···
 #define SORTEXTABLE_64
 #include "sortextable.h"
 
-static int compare_x86_table(const void *a, const void *b)
+static int compare_relative_table(const void *a, const void *b)
 {
 	int32_t av = (int32_t)r(a);
 	int32_t bv = (int32_t)r(b);
···
 	return 0;
 }
 
-static void sort_x86_table(char *extab_image, int image_size)
+static void sort_relative_table(char *extab_image, int image_size)
 {
 	int i;
 
···
 		i += 4;
 	}
 
-	qsort(extab_image, image_size / 8, 8, compare_x86_table);
+	qsort(extab_image, image_size / 8, 8, compare_relative_table);
 
 	/* Now denormalize. */
 	i = 0;
···
 		break;
 	case EM_386:
 	case EM_X86_64:
-		custom_sort = sort_x86_table;
-		break;
 	case EM_S390:
+		custom_sort = sort_relative_table;
+		break;
 	case EM_MIPS:
 		break;
 	}  /* end switch */