re PR libstdc++/3584 (arm-specific atomic operations not atomic)

PR libstdc++/3584
* config/cpu/arm/atomicity.h (__exchange_and_add): Don't try to use
ASM sequences that don't give us atomic addition operations.  Instead
just add a comment explaining why it doesn't work.
(__atomic_add): Just use __exchange_and_add.
(__test_and_set, __always_swap): Delete.

From-SVN: r57778

2 files changed, 23 insertions, 173 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 18bb0d5..d3bb12a 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,12 @@
+2002-10-03  Richard Earnshaw  <rearnsha@arm.com>
+
+	PR libstdc++/3584
+	* config/cpu/arm/atomicity.h (__exchange_and_add): Don't try to use
+	ASM sequences that don't give us atomic addition operations.  Instead
+	just add a comment explaining why it doesn't work.
+	(__atomic_add): Just use __exchange_and_add.
+	(__test_and_set, __always_swap): Delete.
+
 2002-10-02  Andreas Jaeger  <aj@suse.de>
 
 	* config/abi/x86_64-unknown-linux-gnu/baseline_symbols.txt:
diff --git a/libstdc++-v3/config/cpu/arm/atomicity.h b/libstdc++-v3/config/cpu/arm/atomicity.h
index 2363edf..7b952aa 100644
--- a/libstdc++-v3/config/cpu/arm/atomicity.h
+++ b/libstdc++-v3/config/cpu/arm/atomicity.h
@@ -32,51 +32,23 @@
 
 typedef int _Atomic_word;
 
+/* It isn't possible to write an atomic add instruction using the ARM
+   SWP instruction without using either a global guard variable or a
+   guard bit somewhere in the Atomic word.  However, even with a guard
+   bit we need to understand the thread model (if any) in order to
+   make co-operatively threaded applications work correctly.
+
+   The previous Thumb-based implementations were also completely
+   broken, since they failed to switch back into Thumb mode (Gas bug,
+   I think).  */
+
 static inline _Atomic_word
 __attribute__ ((__unused__))
 __exchange_and_add (volatile _Atomic_word* __mem, int __val)
 {
-  _Atomic_word __tmp, __tmp2, __result;
-#ifdef __thumb__
-  /* Since this function is inlined, we can't be sure of the alignment.  */
-  __asm__ __volatile__ (
-	"ldr     %0, 4f \n\t"
-	"bx      %0 \n\t"
-	".align 0 \n"
-	"4:\t"
-	".word   0f \n\t"
-	".code 32 \n"
-	"0:\t"
-	"ldr     %0, [%3] \n\t"
-	"add     %1, %0, %4 \n\t"
-	"swp     %2, %1, [%3] \n\t"
-        "cmp     %0, %2 \n\t"
-        "swpne   %1, %2, [%3] \n\t"
-        "bne     0b \n\t"
-	"ldr     %1, 1f \n\t"
-	"bx      %1 \n"
-	"1:\t"
-	".word   2f \n\t"
-	".code 16 \n"
-	"2:\n"
-	: "=&l"(__result), "=&r"(__tmp), "=&r"(__tmp2) 
-	: "r" (__mem), "r"(__val) 
-	: "cc", "memory");
-#else
-  __asm__ __volatile__ (
-	"\n"
-	"0:\t"
-	"ldr     %0, [%3] \n\t"
-	"add     %1, %0, %4 \n\t"
-	"swp     %2, %1, [%3] \n\t"
-	"cmp     %0, %2 \n\t"
-	"swpne   %1, %2, [%3] \n\t"
-	"bne     0b \n\t"
-	""
-	: "=&r"(__result), "=&r"(__tmp), "=&r"(__tmp2) 
-	: "r" (__mem), "r"(__val) 
-	: "cc", "memory");
-#endif
+  _Atomic_word __result = *__mem;
+
+  *__mem = __result + __val;
   return __result;
 }
 
@@ -84,138 +56,7 @@ static inline void
 __attribute__ ((__unused__))
 __atomic_add (volatile _Atomic_word *__mem, int __val)
 {
-  _Atomic_word __tmp, __tmp2, __tmp3;
-#ifdef __thumb__
-  /* Since this function is inlined, we can't be sure of the alignment.  */
-  __asm__ __volatile__ (
-	"ldr     %0, 4f \n\t"
-	"bx      %0 \n\t"
-	".align 0\n"
-	"4:\t"
-	".word   0f \n\t"
-	".code 32 \n"
-	"0:\t"
-	"ldr     %0, [%3] \n\t"
-	"add     %1, %0, %4 \n\t"
-        "swp     %2, %1, [%3] \n\t"
-        "cmp     %0, %2 \n\t"
-        "swpne   %1, %2,[%3] \n\t"
-        "bne     0b \n\t"
-	"ldr     %1, 1f \n\t"
-	"bx      %1 \n"
-	"1:\t"
-	".word   2f \n\t"
-	".code 16 \n"
-	"2:\n"
-	: "=&l"(__tmp), "=&r"(__tmp2), "=&r"(__tmp3) 
-	: "r" (__mem), "r"(__val) 
-	: "cc", "memory");
-#else
-  __asm__ __volatile__ (
-	"\n"
-	"0:\t"
-	"ldr     %0, [%3] \n\t"
-	"add     %1, %0, %4 \n\t"
-	"swp     %2, %1, [%3] \n\t"
-	"cmp     %0, %2 \n\t"
-	"swpne   %1, %2, [%3] \n\t"
-	"bne     0b \n\t"
-	""
-	: "=&r"(__tmp), "=&r"(__tmp2), "=&r"(__tmp3) 
-	: "r" (__mem), "r"(__val) 
-	: "cc", "memory");
-#endif
-}
-
-static inline long
-__attribute__ ((__unused__))
-__always_swap (volatile long *__p, long __newval)
-{
-  long __result;
-#ifdef __thumb__
-  long __tmp;
-  /* Since this function is inlined, we can't be sure of the alignment.  */
-  __asm__ __volatile__ (
-	"ldr     %0, 4f \n\t"
-	"bx      %0 \n\t"
-	".align 0 \n"
-	"4:\t"
-	".word   0f \n\t"
-	".code 32\n"
-	"0:\t"
-	"swp     %0, %3, [%2] \n\t"
-	"ldr     %1, 1f \n\t"
-	"bx      %1 \n"
-	"1:\t"
-	".word   2f \n\t"
-	".code 16 \n"
-	"2:\n"
-	: "=&l"(__result), "=&r"(__tmp)
-	: "r"(__p), "r"(__newval)
-	: "memory");
-#else
-  __asm__ __volatile__ (
-	"\n\t"
-	"swp     %0, %2, [%1] \n\t"
-	""
-	: "=&r"(__result)
-	: "r"(__p), "r"(__newval)
-	: "memory");
-#endif
-  return __result;
-}
-
-static inline int
-__attribute__ ((__unused__))
-__test_and_set (volatile long *__p, long __newval)
-{
-  int __result;
-  long __tmp;
-#ifdef __thumb__
-  /* Since this function is inlined, we can't be sure of the alignment.  */
-  __asm__ __volatile__ (
-	"ldr     %0, 4f \n\t"
-	"bx      %0 \n\t"
-	".align 0 \n"
-	"4:\t"
-	".word   0f \n\t"
-	".code 32 \n"
-	"0:\t"
-	"ldr     %0, [%2] \n\t"
-        "cmp     %0, #0 \n\t"
-        "bne     1f \n\t"
-        "swp     %1, %3, [%2] \n\t"
-        "cmp     %0, %1 \n\t"
-        "swpne   %0, %1, [%2]\n\t"
-        "bne     0b \n"
-	"1:\t"
-	"ldr     %1, 2f \n\t"
-	"bx      %1 \n"
-	"2:\t"
-	".word   3f \n\t"
-	".code 16 \n"
-	"3:"
-	: "=&l"(__result), "=r" (__tmp) 
-	: "r"(__p), "r"(__newval) 
-	: "cc", "memory");
-#else
-  __asm__ __volatile__ (
-	"\n"
-	"0:\t"
-	"ldr     %0, [%2] \n\t"
-	"cmp     %0, #0 \n\t"
-	"bne     1f \n\t"
-	"swp     %1, %3, [%2] \n\t"
-	"cmp     %0, %1 \n\t"
-	"swpne   %0, %1, [%2] \n\t"
-	"bne     0b \n"
-	"1:\n\t"
-	""
-	: "=&r"(__result), "=r" (__tmp) 
-	: "r"(__p), "r"(__newval) 
-	: "cc", "memory");
-#endif
-  return __result;
+  __exchange_and_add (__mem, __val);
 }
 
 #endif /* atomicity.h */