[PATCH] Add implementations of __readfs{byte, word, dword, qword} to Intrin.h

[Hans Wennborg]

  Thanks for the comments! Here's a new version with all the bells and whistles:

  - volatile ptr, as per David's request
  - using a macro
  - casting __offset to size_t to make sure it's pointer-sized
  - prefix address_space with double underscores to avoid name conflicts.

Hi rnk, whunt,

http://llvm-reviews.chandlerc.com/D2606

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D2606?vs=6611&id=6615#toc

Files:
  lib/Headers/Intrin.h

Index: lib/Headers/Intrin.h
===================================================================
--- lib/Headers/Intrin.h
+++ lib/Headers/Intrin.h
@@ -101,9 +101,13 @@
 unsigned long __readcr8(void);
 unsigned int __readdr(unsigned int);
 unsigned int __readeflags(void);
+static __inline__
 unsigned char __readfsbyte(unsigned long);
+static __inline__
 unsigned long __readfsdword(unsigned long);
+static __inline__
 unsigned __int64 __readfsqword(unsigned long);
+static __inline__
 unsigned short __readfsword(unsigned long);
 unsigned __int64 __readmsr(unsigned long);
 unsigned __int64 __readpmc(unsigned long);
@@ -767,6 +771,32 @@
   __asm__ volatile ("" : : : "memory");
 }
 /*----------------------------------------------------------------------------*\
+|* readfs 
+|* (Pointers in address space #257 are relative to the FS segment register.)
+\*----------------------------------------------------------------------------*/
+#define __ptr_to_addr_space(__addr_space_nbr, __type, __offset)              \
+    ((volatile __type __attribute__((__address_space__(__addr_space_nbr)))*) \
+    (size_t)(__offset))
+
+static __inline__ unsigned char __attribute__((__always_inline__, __nodebug__))
+__readfsbyte(unsigned long __offset) {
+  return *__ptr_to_addr_space(257, unsigned char, __offset);
+}
+static __inline__ unsigned long __attribute__((__always_inline__, __nodebug__))
+__readfsdword(unsigned long __offset) {
+  return *__ptr_to_addr_space(257, unsigned long, __offset);
+}
+static __inline__ unsigned __int64 __attribute__((__always_inline__, __nodebug__))
+__readfsqword(unsigned long __offset) {
+  return *__ptr_to_addr_space(257, unsigned __int64, __offset);
+}
+static __inline__ unsigned short __attribute__((__always_inline__, __nodebug__))
+__readfsword(unsigned long __offset) {
+  return *__ptr_to_addr_space(257, unsigned short, __offset);
+}
+
+#undef __ptr_to_addr_space
+/*----------------------------------------------------------------------------*\
 |* Misc
 \*----------------------------------------------------------------------------*/
 static __inline__ void * __attribute__((__always_inline__, __nodebug__))
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