powerpc: Add support for relative exception tables

This halves the exception table size on 64-bit builds, and it allows
build-time sorting of exception tables to work on relocated kernels.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Minor asm fixups and bits to keep the selftests working]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/ppc_asm.h

@@ -785,9 +785,9 @@ END_FTR_SECTION_IFCLR(CPU_FTR_601)
  */
 #define EX_TABLE(_fault, _target)		\
 	stringify_in_c(.section __ex_table,"a";)\
-	PPC_LONG_ALIGN stringify_in_c(;)	\
-	PPC_LONG stringify_in_c(_fault;)	\
-	PPC_LONG stringify_in_c(_target;)	\
+	stringify_in_c(.balign 4;)		\
+	stringify_in_c(.long (_fault) - . ;)	\
+	stringify_in_c(.long (_target) - . ;)	\
 	stringify_in_c(.previous)
 
 #endif /* _ASM_POWERPC_PPC_ASM_H */

arch/powerpc/include/asm/uaccess.h

@@ -64,23 +64,30 @@
 	 __access_ok((__force unsigned long)(addr), (size), get_fs()))
 
 /*
- * The exception table consists of pairs of addresses: the first is the
- * address of an instruction that is allowed to fault, and the second is
+ * The exception table consists of pairs of relative addresses: the first is
+ * the address of an instruction that is allowed to fault, and the second is
  * the address at which the program should continue.  No registers are
- * modified, so it is entirely up to the continuation code to figure out
- * what to do.
+ * modified, so it is entirely up to the continuation code to figure out what
+ * to do.
  *
- * All the routines below use bits of fixup code that are out of line
- * with the main instruction path.  This means when everything is well,
- * we don't even have to jump over them.  Further, they do not intrude
- * on our cache or tlb entries.
+ * All the routines below use bits of fixup code that are out of line with the
+ * main instruction path.  This means when everything is well, we don't even
+ * have to jump over them.  Further, they do not intrude on our cache or tlb
+ * entries.
  */
 
+#define ARCH_HAS_RELATIVE_EXTABLE
+
 struct exception_table_entry {
-	unsigned long insn;
-	unsigned long fixup;
+	int insn;
+	int fixup;
 };
 
+static inline unsigned long extable_fixup(const struct exception_table_entry *x)
+{
+	return (unsigned long)&x->fixup + x->fixup;
+}
+
 /*
  * These are the main single-value transfer routines.  They automatically
  * use the right size if we just have the right pointer type.

arch/powerpc/kernel/kprobes.c

@@ -449,7 +449,7 @@ int __kprobes kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 		 * zero, try to fix up.
 		 */
 		if ((entry = search_exception_tables(regs->nip)) != NULL) {
-			regs->nip = entry->fixup;
+			regs->nip = extable_fixup(entry);
 			return 1;
 		}
 

arch/powerpc/kernel/traps.c

@@ -365,7 +365,7 @@ static inline int check_io_access(struct pt_regs *regs)
 			       (*nip & 0x100)? "OUT to": "IN from",
 			       regs->gpr[rb] - _IO_BASE, nip);
 			regs->msr |= MSR_RI;
-			regs->nip = entry->fixup;
+			regs->nip = extable_fixup(entry);
 			return 1;
 		}
 	}

arch/powerpc/mm/fault.c

@@ -512,7 +512,7 @@ void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
 
 	/* Are we prepared to handle this fault?  */
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
-		regs->nip = entry->fixup;
+		regs->nip = extable_fixup(entry);
 		return;
 	}
 

arch/powerpc/platforms/embedded6xx/holly.c

@@ -263,7 +263,7 @@ static int ppc750_machine_check_exception(struct pt_regs *regs)
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
 		tsi108_clear_pci_cfg_error();
 		regs->msr |= MSR_RI;
-		regs->nip = entry->fixup;
+		regs->nip = extable_fixup(entry);
 		return 1;
 	}
 	return 0;

arch/powerpc/platforms/embedded6xx/mpc7448_hpc2.c

@@ -174,7 +174,7 @@ static int mpc7448_machine_check_exception(struct pt_regs *regs)
 	if ((entry = search_exception_tables(regs->nip)) != NULL) {
 		tsi108_clear_pci_cfg_error();
 		regs->msr |= MSR_RI;
-		regs->nip = entry->fixup;
+		regs->nip = extable_fixup(entry);
 		return 1;
 	}
 	return 0;

arch/powerpc/sysdev/fsl_rio.c

@@ -111,7 +111,7 @@ int fsl_rio_mcheck_exception(struct pt_regs *regs)
 			out_be32((u32 *)(rio_regs_win + RIO_LTLEDCSR),
 				 0);
 			regs->msr |= MSR_RI;
-			regs->nip = entry->fixup;
+			regs->nip = extable_fixup(entry);
 			return 1;
 		}
 	}

tools/testing/selftests/powerpc/primitives/load_unaligned_zeropad.c

@@ -73,19 +73,23 @@ extern char __stop___ex_table[];
 #error implement UCONTEXT_NIA
 #endif
 
+struct extbl_entry {
+	int insn;
+	int fixup;
+};
 
 static void segv_handler(int signr, siginfo_t *info, void *ptr)
 {
 	ucontext_t *uc = (ucontext_t *)ptr;
 	unsigned long addr = (unsigned long)info->si_addr;
 	unsigned long *ip = &UCONTEXT_NIA(uc);
-	unsigned long *ex_p = (unsigned long *)__start___ex_table;
+	struct extbl_entry *entry = (struct extbl_entry *)__start___ex_table;
 
-	while (ex_p < (unsigned long *)__stop___ex_table) {
+	while (entry < (struct extbl_entry *)__stop___ex_table) {
 		unsigned long insn, fixup;
 
-		insn = *ex_p++;
-		fixup = *ex_p++;
+		insn  = (unsigned long)&entry->insn + entry->insn;
+		fixup = (unsigned long)&entry->fixup + entry->fixup;
 
 		if (insn == *ip) {
 			*ip = fixup;