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[PATCH v2 0/6] generic relative extable support

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  [PATCH v2 0/6] generic relative extable support Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-01-05 16:30 +0100
    [PATCH v2 6/6] arm64: switch to relative exception tables Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-01-05 16:30 +0100
    [PATCH v2 1/6] extable: add support for relative extables to search and sort routines Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-01-05 16:30 +0100
    [PATCH v2 4/6] x86/extable: use generic search and sort routines Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-01-05 16:30 +0100
    Re: [PATCH v2 0/6] generic relative extable support Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-01-11 15:00 +0100
      Re: [PATCH v2 0/6] generic relative extable support Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-01-14 09:00 +0100

#1301608 — [PATCH v2 0/6] generic relative extable support

There are currently four architectures (x86, ia64, alpha and s390) whose
user-access exception tables are relative to the table entry address rather
than absolute. Each of these architectures has its own search_extable() and
sort_extable() implementation, which are not only mostly identical to each
other, but also deviate very little from the generic absolute implementations
in lib/extable.c that they override.

So before making arm64 the fifth architecture that reimplements this, let's
refactor the existing code so that all of these architectures use common code
for searching and sorting the relative extables. Archs may set
ARCH_HAS_RELATIVE_EXTABLE to indicate that the table consists of a pair of
relative ints, and may define swap_ex_entry_fixup() if the fixup member needs
special treatment in the swapping step of the sorting routine (such as alpha).

Changes since v2:
- introduce the _ASM_EXTABLE() cpp macro for arm64, and replace all open coded
  exception table entries with it, including an instance I missed in v1 in
  asm/word-at-a-time.h (suggested by hpa)
- added acks to from arch maintainers

No acks yet for the arch/alpha patch.
 
NOTE: I took the liberty of carrying over each arch specific ack to the generic
shared first patch, since they are tightly coupled anyway. If anyone objects to
this, please let me know.

Also note that the s390 patch applies on top of the following patch:

  http://article.gmane.org/gmane.linux.kernel/2117036

which fixes a bug I spotted while working on this code. Since that probably
needs to go to -stable, I broke it out and posted it separately.

Ard Biesheuvel (6):
  extable: add support for relative extables to search and sort routines
  alpha/extable: use generic search and sort routines
  s390/extable: use generic search and sort routines
  x86/extable: use generic search and sort routines
  ia64/extable: use generic search and sort routines
  arm64: switch to relative exception tables

 arch/alpha/include/asm/uaccess.h        |  10 +-
 arch/alpha/mm/Makefile                  |   2 +-
 arch/alpha/mm/extable.c                 |  92 -----------------
 arch/arm64/include/asm/assembler.h      |  15 ++-
 arch/arm64/include/asm/futex.h          |  12 +--
 arch/arm64/include/asm/uaccess.h        |  30 +++---
 arch/arm64/include/asm/word-at-a-time.h |   7 +-
 arch/arm64/kernel/armv8_deprecated.c    |   7 +-
 arch/arm64/mm/extable.c                 |   2 +-
 arch/ia64/include/asm/uaccess.h         |   8 +-
 arch/ia64/mm/extable.c                  |  97 +-----------------
 arch/s390/include/asm/uaccess.h         |   8 +-
 arch/s390/mm/Makefile                   |   2 +-
 arch/s390/mm/extable.c                  |  85 ----------------
 arch/x86/include/asm/uaccess.h          |   5 +-
 arch/x86/mm/extable.c                   | 106 +-------------------
 lib/extable.c                           |  50 +++++++--
 scripts/sortextable.c                   |   2 +-
 18 files changed, 98 insertions(+), 442 deletions(-)
 delete mode 100644 arch/alpha/mm/extable.c
 delete mode 100644 arch/s390/mm/extable.c

-- 
2.5.0

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#1301609 — [PATCH v2 6/6] arm64: switch to relative exception tables

Instead of using absolute addresses for both the exception location
and the fixup, use offsets relative to the exception table entry values.
Not only does this cut the size of the exception table in half, it is
also a prerequisite for KASLR, since absolute exception table entries
are subject to dynamic relocation, which is incompatible with the sorting
of the exception table that occurs at build time.

This patch also introduces the _ASM_EXTABLE preprocessor macro (which
exists on x86 as well) and its _asm_extable assembly counterpart, as
shorthands to emit exception table entries.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm64/include/asm/assembler.h      | 15 +++++++---
 arch/arm64/include/asm/futex.h          | 12 +++-----
 arch/arm64/include/asm/uaccess.h        | 30 +++++++++++---------
 arch/arm64/include/asm/word-at-a-time.h |  7 ++---
 arch/arm64/kernel/armv8_deprecated.c    |  7 ++---
 arch/arm64/mm/extable.c                 |  2 +-
 scripts/sortextable.c                   |  2 +-
 7 files changed, 38 insertions(+), 37 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 12eff928ef8b..8c1c2f6a1b1b 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -94,12 +94,19 @@
 	dmb	\opt
 	.endm
 
+/*
+ * Emit an entry into the exception table
+ */
+	.macro		_asm_extable, from, to
+	.pushsection	__ex_table, "a"
+	.align		3
+	.long		(\from - .), (\to - .)
+	.popsection
+	.endm
+
 #define USER(l, x...)				\
 9999:	x;					\
-	.section __ex_table,"a";		\
-	.align	3;				\
-	.quad	9999b,l;			\
-	.previous
+	_asm_extable	9999b, l
 
 /*
  * Register aliases.
diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index 007a69fc4f40..1ab15a3b5a0e 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -42,10 +42,8 @@
 "4:	mov	%w0, %w5\n"						\
 "	b	3b\n"							\
 "	.popsection\n"							\
-"	.pushsection __ex_table,\"a\"\n"				\
-"	.align	3\n"							\
-"	.quad	1b, 4b, 2b, 4b\n"					\
-"	.popsection\n"							\
+	_ASM_EXTABLE(1b, 4b)						\
+	_ASM_EXTABLE(2b, 4b)						\
 	ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,		\
 		    CONFIG_ARM64_PAN)					\
 	: "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp)	\
@@ -133,10 +131,8 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 "4:	mov	%w0, %w6\n"
 "	b	3b\n"
 "	.popsection\n"
-"	.pushsection __ex_table,\"a\"\n"
-"	.align	3\n"
-"	.quad	1b, 4b, 2b, 4b\n"
-"	.popsection\n"
+	_ASM_EXTABLE(1b, 4b)
+	_ASM_EXTABLE(2b, 4b)
 	: "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp)
 	: "r" (oldval), "r" (newval), "Ir" (-EFAULT)
 	: "memory");
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index b2ede967fe7d..dc11577fab7e 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -36,11 +36,11 @@
 #define VERIFY_WRITE 1
 
 /*
- * 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 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.
+ * The exception table consists of pairs of relative offsets: the first
+ * is the relative offset to an instruction that is allowed to fault,
+ * and the second is the relative offset 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.
  *
  * 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,
@@ -50,9 +50,11 @@
 
 struct exception_table_entry
 {
-	unsigned long insn, fixup;
+	int insn, fixup;
 };
 
+#define ARCH_HAS_RELATIVE_EXTABLE
+
 extern int fixup_exception(struct pt_regs *regs);
 
 #define KERNEL_DS	(-1UL)
@@ -105,6 +107,12 @@ static inline void set_fs(mm_segment_t fs)
 #define access_ok(type, addr, size)	__range_ok(addr, size)
 #define user_addr_max			get_fs
 
+#define _ASM_EXTABLE(from, to)						\
+	"	.pushsection	__ex_table, \"a\"\n"			\
+	"	.align		3\n"					\
+	"	.long		(" #from " - .), (" #to " - .)\n"	\
+	"	.popsection\n"
+
 /*
  * The "__xxx" versions of the user access functions do not verify the address
  * space - it must have been done previously with a separate "access_ok()"
@@ -123,10 +131,7 @@ static inline void set_fs(mm_segment_t fs)
 	"	mov	%1, #0\n"					\
 	"	b	2b\n"						\
 	"	.previous\n"						\
-	"	.section __ex_table,\"a\"\n"				\
-	"	.align	3\n"						\
-	"	.quad	1b, 3b\n"					\
-	"	.previous"						\
+	_ASM_EXTABLE(1b, 3b)						\
 	: "+r" (err), "=&r" (x)						\
 	: "r" (addr), "i" (-EFAULT))
 
@@ -190,10 +195,7 @@ do {									\
 	"3:	mov	%w0, %3\n"					\
 	"	b	2b\n"						\
 	"	.previous\n"						\
-	"	.section __ex_table,\"a\"\n"				\
-	"	.align	3\n"						\
-	"	.quad	1b, 3b\n"					\
-	"	.previous"						\
+	_ASM_EXTABLE(1b, 3b)						\
 	: "+r" (err)							\
 	: "r" (x), "r" (addr), "i" (-EFAULT))
 
diff --git a/arch/arm64/include/asm/word-at-a-time.h b/arch/arm64/include/asm/word-at-a-time.h
index aab5bf09e9d9..6fe9b8efaff5 100644
--- a/arch/arm64/include/asm/word-at-a-time.h
+++ b/arch/arm64/include/asm/word-at-a-time.h
@@ -20,6 +20,8 @@
 
 #include <linux/kernel.h>
 
+#include <asm/uaccess.h>
+
 struct word_at_a_time {
 	const unsigned long one_bits, high_bits;
 };
@@ -81,10 +83,7 @@ static inline unsigned long load_unaligned_zeropad(const void *addr)
 #endif
 	"	b	2b\n"
 	"	.popsection\n"
-	"	.pushsection __ex_table,\"a\"\n"
-	"	.align	3\n"
-	"	.quad	1b, 3b\n"
-	"	.popsection"
+	_ASM_EXTABLE(1b, 3b)
 	: "=&r" (ret), "=&r" (offset)
 	: "r" (addr), "Q" (*(unsigned long *)addr));
 
diff --git a/arch/arm64/kernel/armv8_deprecated.c b/arch/arm64/kernel/armv8_deprecated.c
index 937f5e58a4d3..a6102eeda46c 100644
--- a/arch/arm64/kernel/armv8_deprecated.c
+++ b/arch/arm64/kernel/armv8_deprecated.c
@@ -297,11 +297,8 @@ static void register_insn_emulation_sysctl(struct ctl_table *table)
 	"4:	mov		%w0, %w5\n"			\
 	"	b		3b\n"				\
 	"	.popsection"					\
-	"	.pushsection	 __ex_table,\"a\"\n"		\
-	"	.align		3\n"				\
-	"	.quad		0b, 4b\n"			\
-	"	.quad		1b, 4b\n"			\
-	"	.popsection\n"					\
+	_ASM_EXTABLE(0b, 4b)					\
+	_ASM_EXTABLE(1b, 4b)					\
 	ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,	\
 		CONFIG_ARM64_PAN)				\
 	: "=&r" (res), "+r" (data), "=&r" (temp)		\
diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
index 79444279ba8c..81acd4706878 100644
--- a/arch/arm64/mm/extable.c
+++ b/arch/arm64/mm/extable.c
@@ -11,7 +11,7 @@ int fixup_exception(struct pt_regs *regs)
 
 	fixup = search_exception_tables(instruction_pointer(regs));
 	if (fixup)
-		regs->pc = fixup->fixup;
+		regs->pc = (unsigned long)&fixup->fixup + fixup->fixup;
 
 	return fixup != NULL;
 }
diff --git a/scripts/sortextable.c b/scripts/sortextable.c
index c2423d913b46..af247c70fb66 100644
--- a/scripts/sortextable.c
+++ b/scripts/sortextable.c
@@ -282,12 +282,12 @@ do_file(char const *const fname)
 	case EM_386:
 	case EM_X86_64:
 	case EM_S390:
+	case EM_AARCH64:
 		custom_sort = sort_relative_table;
 		break;
 	case EM_ARCOMPACT:
 	case EM_ARCV2:
 	case EM_ARM:
-	case EM_AARCH64:
 	case EM_MICROBLAZE:
 	case EM_MIPS:
 	case EM_XTENSA:
-- 
2.5.0

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#1301610 — [PATCH v2 1/6] extable: add support for relative extables to search and sort routines

This adds support to the generic search_extable() and sort_extable()
implementations for dealing with exception table entries whose fields
contain relative offsets rather than absolute addresses.

Acked-by: Helge Deller <deller@gmx.de>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Acked-by: Tony Luck <tony.luck@intel.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 lib/extable.c | 50 ++++++++++++++++----
 1 file changed, 41 insertions(+), 9 deletions(-)

diff --git a/lib/extable.c b/lib/extable.c
index 4cac81ec225e..0be02ad561e9 100644
--- a/lib/extable.c
+++ b/lib/extable.c
@@ -14,7 +14,37 @@
 #include <linux/sort.h>
 #include <asm/uaccess.h>
 
+#ifndef ARCH_HAS_RELATIVE_EXTABLE
+#define ex_to_insn(x)	((x)->insn)
+#else
+static inline unsigned long ex_to_insn(const struct exception_table_entry *x)
+{
+	return (unsigned long)&x->insn + x->insn;
+}
+#endif
+
 #ifndef ARCH_HAS_SORT_EXTABLE
+#ifndef ARCH_HAS_RELATIVE_EXTABLE
+#define swap_ex		NULL
+#else
+static void swap_ex(void *a, void *b, int size)
+{
+	struct exception_table_entry *x = a, *y = b, tmp;
+	int delta = b - a;
+
+	tmp = *x;
+	x->insn = y->insn + delta;
+	y->insn = tmp.insn - delta;
+
+#ifdef swap_ex_entry_fixup
+	swap_ex_entry_fixup(x, y, tmp, delta);
+#else
+	x->fixup = y->fixup + delta;
+	y->fixup = tmp.fixup - delta;
+#endif
+}
+#endif /* ARCH_HAS_RELATIVE_EXTABLE */
+
 /*
  * The exception table needs to be sorted so that the binary
  * search that we use to find entries in it works properly.
@@ -26,9 +56,9 @@ static int cmp_ex(const void *a, const void *b)
 	const struct exception_table_entry *x = a, *y = b;
 
 	/* avoid overflow */
-	if (x->insn > y->insn)
+	if (ex_to_insn(x) > ex_to_insn(y))
 		return 1;
-	if (x->insn < y->insn)
+	if (ex_to_insn(x) < ex_to_insn(y))
 		return -1;
 	return 0;
 }
@@ -37,7 +67,7 @@ void sort_extable(struct exception_table_entry *start,
 		  struct exception_table_entry *finish)
 {
 	sort(start, finish - start, sizeof(struct exception_table_entry),
-	     cmp_ex, NULL);
+	     cmp_ex, swap_ex);
 }
 
 #ifdef CONFIG_MODULES
@@ -48,13 +78,15 @@ void sort_extable(struct exception_table_entry *start,
 void trim_init_extable(struct module *m)
 {
 	/*trim the beginning*/
-	while (m->num_exentries && within_module_init(m->extable[0].insn, m)) {
+	while (m->num_exentries &&
+	       within_module_init(ex_to_insn(&m->extable[0]), m)) {
 		m->extable++;
 		m->num_exentries--;
 	}
 	/*trim the end*/
 	while (m->num_exentries &&
-		within_module_init(m->extable[m->num_exentries-1].insn, m))
+	       within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]),
+				  m))
 		m->num_exentries--;
 }
 #endif /* CONFIG_MODULES */
@@ -81,13 +113,13 @@ search_extable(const struct exception_table_entry *first,
 		 * careful, the distance between value and insn
 		 * can be larger than MAX_LONG:
 		 */
-		if (mid->insn < value)
+		if (ex_to_insn(mid) < value)
 			first = mid + 1;
-		else if (mid->insn > value)
+		else if (ex_to_insn(mid) > value)
 			last = mid - 1;
 		else
 			return mid;
-        }
-        return NULL;
+	}
+	return NULL;
 }
 #endif
-- 
2.5.0

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#1301611 — [PATCH v2 4/6] x86/extable: use generic search and sort routines

Replace the arch specific versions of search_extable() and sort_extable()
with calls to the generic ones, which now support relative exception
tables as well.

Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/x86/include/asm/uaccess.h |   5 +-
 arch/x86/mm/extable.c          | 106 +-------------------
 2 files changed, 4 insertions(+), 107 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 09b1b0ab94b7..6d130c4cb7de 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -106,9 +106,8 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
 struct exception_table_entry {
 	int insn, fixup;
 };
-/* This is not the generic standard exception_table_entry format */
-#define ARCH_HAS_SORT_EXTABLE
-#define ARCH_HAS_SEARCH_EXTABLE
+
+#define ARCH_HAS_RELATIVE_EXTABLE
 
 extern int fixup_exception(struct pt_regs *regs);
 extern int early_fixup_exception(unsigned long *ip);
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 903ec1e9c326..0b172b656f43 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -1,14 +1,9 @@
+
 #include <linux/module.h>
-#include <linux/spinlock.h>
-#include <linux/sort.h>
+
 #include <asm/uaccess.h>
 
 static inline unsigned long
-ex_insn_addr(const struct exception_table_entry *x)
-{
-	return (unsigned long)&x->insn + x->insn;
-}
-static inline unsigned long
 ex_fixup_addr(const struct exception_table_entry *x)
 {
 	return (unsigned long)&x->fixup + x->fixup;
@@ -70,100 +65,3 @@ int __init early_fixup_exception(unsigned long *ip)
 
 	return 0;
 }
-
-/*
- * 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)
-{
-	while (first <= last) {
-		const struct exception_table_entry *mid;
-		unsigned long addr;
-
-		mid = ((last - first) >> 1) + first;
-		addr = ex_insn_addr(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 value will always end up fittin in an int, because on
-	 * both i386 and x86-64 the kernel symbol-reachable address
-	 * space is < 2 GiB.
-	 *
-	 * 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;
-
-	/* Convert all entries to being relative to the start of the section */
-	i = 0;
-	for (p = start; p < finish; p++) {
-		p->insn += i;
-		i += 4;
-		p->fixup += i;
-		i += 4;
-	}
-
-	sort(start, finish - start, sizeof(struct exception_table_entry),
-	     cmp_ex, NULL);
-
-	/* Denormalize all entries */
-	i = 0;
-	for (p = start; p < finish; p++) {
-		p->insn -= i;
-		i += 4;
-		p->fixup -= i;
-		i += 4;
-	}
-}
-
-#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(ex_insn_addr(&m->extable[0]), m)) {
-		m->extable++;
-		m->num_exentries--;
-	}
-	/*trim the end*/
-	while (m->num_exentries &&
-	       within_module_init(ex_insn_addr(&m->extable[m->num_exentries-1]), m))
-		m->num_exentries--;
-}
-#endif /* CONFIG_MODULES */
-- 
2.5.0

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#1306228

On 5 January 2016 at 16:19, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> There are currently four architectures (x86, ia64, alpha and s390) whose
> user-access exception tables are relative to the table entry address rather
> than absolute. Each of these architectures has its own search_extable() and
> sort_extable() implementation, which are not only mostly identical to each
> other, but also deviate very little from the generic absolute implementations
> in lib/extable.c that they override.
>
> So before making arm64 the fifth architecture that reimplements this, let's
> refactor the existing code so that all of these architectures use common code
> for searching and sorting the relative extables. Archs may set
> ARCH_HAS_RELATIVE_EXTABLE to indicate that the table consists of a pair of
> relative ints, and may define swap_ex_entry_fixup() if the fixup member needs
> special treatment in the swapping step of the sorting routine (such as alpha).
>

[...]

Now that I have collected acks for all the patches, I think this is
good to go in.

@Andrew: since this touches 5 different architectures, is this perhaps
something that could go in via your tree after -rc1?
(assuming that the s390 bugfix has been merged by then)

Thanks,
Ard.

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#1309062

On Mon, Jan 11, 2016 at 02:59:46PM +0100, Ard Biesheuvel wrote:
> On 5 January 2016 at 16:19, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > There are currently four architectures (x86, ia64, alpha and s390) whose
> > user-access exception tables are relative to the table entry address rather
> > than absolute. Each of these architectures has its own search_extable() and
> > sort_extable() implementation, which are not only mostly identical to each
> > other, but also deviate very little from the generic absolute implementations
> > in lib/extable.c that they override.
> >
> > So before making arm64 the fifth architecture that reimplements this, let's
> > refactor the existing code so that all of these architectures use common code
> > for searching and sorting the relative extables. Archs may set
> > ARCH_HAS_RELATIVE_EXTABLE to indicate that the table consists of a pair of
> > relative ints, and may define swap_ex_entry_fixup() if the fixup member needs
> > special treatment in the swapping step of the sorting routine (such as alpha).
> >
> 
> [...]
> 
> Now that I have collected acks for all the patches, I think this is
> good to go in.
> 
> @Andrew: since this touches 5 different architectures, is this perhaps
> something that could go in via your tree after -rc1?
> (assuming that the s390 bugfix has been merged by then)

Your s390 bugfix has been merged.  See git commit id bcb7825a77f4 ("s390:
fix normalization bug in exception table sorting").

Thanks,
Heiko

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