Revert "Revert "arm64/mm: Limit TASK_SIZE_64 ..." and add breaks on incompatible mozjs"

This reverts commit a462c39f5d.  mozjs24
got 'fixed' in an ABI-compatible way that had to be reverted, so it's
still broken.  Same for mozjs, though it hasn't been reverted yet.

Also, Breaks relations against source package names would not have
been very effective.

debian/changelog

@@ -1,10 +1,3 @@
-linux (4.9~rc8-1~exp2) UNRELEASED; urgency=medium
-
-  * [arm64] Revert "arm64/mm: Limit TASK_SIZE_64 ..." and add breaks on
-    incompatible mozjs
-
- -- Ben Hutchings <ben@decadent.org.uk>  Fri, 09 Dec 2016 12:11:34 +0000
-
 linux (4.9~rc8-1~exp1) experimental; urgency=medium
 
   * New upstream release candidate

debian/config/arm64/defines

@@ -10,7 +10,6 @@ vdso: true
 
 [image]
 install-stem: vmlinuz
-breaks: mozjs (<< 1.8.5-1.0.0+dfsg-5.1~), mozjs24 (<< 24.2.0-4~)
 
 [arm64_description]
 hardware: 64-bit ARMv8 machines

debian/patches/bugfix/arm64/arm64-mm-limit-task_size_64-for-compatibility.patch

@@ -0,0 +1,27 @@
+From: Ben Hutchings <ben@decadent.org.uk>
+Date: Fri, 16 Sep 2016 16:32:23 +0100
+Subject: arm64/mm: Limit TASK_SIZE_64 for compatibility
+
+Some programs assume they can use 17 tag bits in a 64-bit pointer,
+which works on most other 64-bit architectures but not on arm64 with
+CONFIG_ARM64_VA_BITS_48.  To maintain compatibility with these
+programs, limit TASK_SIZE_64 to a maximum of 1 << 47.
+
+Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
+---
+
+--- a/arch/arm64/include/asm/memory.h
++++ b/arch/arm64/include/asm/memory.h
+@@ -74,7 +74,12 @@
+ #define PCI_IO_END		(VMEMMAP_START - SZ_2M)
+ #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
+ #define FIXADDR_TOP		(PCI_IO_START - SZ_2M)
++#if VA_BITS <= 47
+ #define TASK_SIZE_64		(UL(1) << VA_BITS)
++#else
++/* User-space might use up to 17 tag bits in 64-bit pointers */
++#define TASK_SIZE_64		(UL(1) << 47)
++#endif
+ 
+ #ifdef CONFIG_COMPAT
+ #define TASK_SIZE_32		UL(0x100000000)

debian/patches/series

@@ -46,6 +46,7 @@ bugfix/x86/viafb-autoload-on-olpc-xo1.5-only.patch
 debian/fanotify-taint-on-use-of-fanotify_access_permissions.patch
 
 # Arch bug fixes
+bugfix/arm64/arm64-mm-limit-task_size_64-for-compatibility.patch
 
 # Arch features
 features/mips/MIPS-increase-MAX-PHYSMEM-BITS-on-Loongson-3-only.patch