[PATCH 2/3] xen/err: Support an optional per-arch slide for the error region

[Andrew Cooper <andrew.cooper3@citrix.com>]

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/include/xen/err.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/xen/include/xen/err.h b/xen/include/xen/err.h
index ef77992..bea7fa3 100644
--- a/xen/include/xen/err.h
+++ b/xen/include/xen/err.h
@@ -15,19 +15,28 @@
  */
 #define MAX_ERRNO	4095
 
+/*
+ * Individual architectures may wish to slide the error region away from its
+ * default position at the very top of virtual address space.  (e.g. if Xen
+ * doesn't own the range).
+ */
+#ifndef ARCH_ERR_PTR_SLIDE
+#define ARCH_ERR_PTR_SLIDE 0
+#endif
+
 static inline bool IS_ERR_VALUE(unsigned long x)
 {
-	return x >= (unsigned long)-MAX_ERRNO;
+	return (x + ARCH_ERR_PTR_SLIDE) >= (unsigned long)-MAX_ERRNO;
 }
 
 static inline void *__must_check ERR_PTR(long error)
 {
-	return (void *)error;
+	return (void *)((unsigned long)error - ARCH_ERR_PTR_SLIDE);
 }
 
 static inline long __must_check PTR_ERR(const void *ptr)
 {
-	return (long)ptr;
+	return (long)((unsigned long)ptr + ARCH_ERR_PTR_SLIDE);
 }
 
 static inline bool __must_check IS_ERR(const void *ptr)
-- 
2.1.4


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