sync/atomic, runtime/internal/atomic: don't assume reads from 0 fail

For a misaligned address force a panic rather than assuming that reading
    from the address 0 will cause one.
    
    Reviewed-on: https://go-review.googlesource.com/69850

From-SVN: r254610

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-7fd845bd9414c348bfa30bd24aa0bb8e4eebf83a
+b03c5dc36d6d0c0d3bef434936e8b924d253595b
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/runtime/internal/atomic/atomic.c

@@ -34,7 +34,7 @@ uint64_t
 Load64 (uint64_t *ptr)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_load_n (ptr, __ATOMIC_ACQUIRE);
 }
 
@@ -66,7 +66,7 @@ int64_t
 Loadint64 (int64_t *ptr)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_load_n (ptr, __ATOMIC_ACQUIRE);
 }
 
@@ -88,7 +88,7 @@ uint64_t
 Xadd64 (uint64_t *ptr, int64_t delta)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_add_fetch (ptr, (uint64_t) delta, __ATOMIC_SEQ_CST);
 }
 
@@ -110,7 +110,7 @@ int64_t
 Xaddint64 (int64_t *ptr, int64_t delta)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_add_fetch (ptr, delta, __ATOMIC_SEQ_CST);
 }
 
@@ -132,7 +132,7 @@ uint64_t
 Xchg64 (uint64_t *ptr, uint64_t new)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_exchange_n (ptr, new, __ATOMIC_SEQ_CST);
 }
 
@@ -184,7 +184,7 @@ _Bool
 Cas64 (uint64_t *ptr, uint64_t old, uint64_t new)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   return __atomic_compare_exchange_n (ptr, &old, new, false, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED);
 }
 
@@ -226,7 +226,7 @@ void
 Store64 (uint64_t *ptr, uint64_t val)
 {
   if (((uintptr_t) ptr & 7) != 0)
-    ptr = NULL;
+    panicmem ();
   __atomic_store_n (ptr, val, __ATOMIC_SEQ_CST);
 }
 

libgo/go/runtime/panic.go

@@ -22,6 +22,7 @@ import (
 //go:linkname makefuncreturning runtime.makefuncreturning
 //go:linkname gorecover runtime.gorecover
 //go:linkname deferredrecover runtime.deferredrecover
+//go:linkname panicmem runtime.panicmem
 // Temporary for C code to call:
 //go:linkname throw runtime.throw
 

libgo/go/sync/atomic/atomic.c

@@ -26,7 +26,7 @@ int64_t
 SwapInt64 (int64_t *addr, int64_t new)
 {
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   return __atomic_exchange_n (addr, new, __ATOMIC_SEQ_CST);
 }
 
@@ -48,7 +48,7 @@ uint64_t
 SwapUint64 (uint64_t *addr, uint64_t new)
 {
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   return __atomic_exchange_n (addr, new, __ATOMIC_SEQ_CST);
 }
 
@@ -215,7 +215,7 @@ LoadInt64 (int64_t *addr)
   int64_t v;
 
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   v = *addr;
   while (! __sync_bool_compare_and_swap (addr, v, v))
     v = *addr;
@@ -247,7 +247,7 @@ LoadUint64 (uint64_t *addr)
   uint64_t v;
 
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   v = *addr;
   while (! __sync_bool_compare_and_swap (addr, v, v))
     v = *addr;
@@ -308,7 +308,7 @@ StoreInt64 (int64_t *addr, int64_t val)
   int64_t v;
 
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   v = *addr;
   while (! __sync_bool_compare_and_swap (addr, v, val))
     v = *addr;
@@ -338,7 +338,7 @@ StoreUint64 (uint64_t *addr, uint64_t val)
   uint64_t v;
 
   if (((uintptr_t) addr & 7) != 0)
-    addr = NULL;
+    panicmem ();
   v = *addr;
   while (! __sync_bool_compare_and_swap (addr, v, val))
     v = *addr;

libgo/runtime/runtime.h

@@ -211,6 +211,8 @@ extern	uint32	runtime_panicking(void)
 extern	bool	runtime_isstarted;
 extern	bool	runtime_isarchive;
 
+extern	void	panicmem(void) __asm__ (GOSYM_PREFIX "runtime.panicmem");
+
 /*
  * common functions and data
  */