runtime: adapt memory management to AIX mmap

On AIX:
* mmap does not allow to map an already mapped range,
* mmap range start at 0x30000000 for 32 bits processes,
* mmap range start at 0x70000000_00000000 for 64 bits processes

Issue golang/go#19200

Change-Id: I1a71214adc44cfff53077534e17962770e7b57a1
Reviewed-on: https://go-review.googlesource.com/37845
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Author: MatthieuSarter

libgo/runtime/malloc.goc

@@ -39,6 +39,10 @@ package runtime
 #ifdef __aarch64__
 #define HeapBase(i) ((void*)(uintptr)(0x40ULL<<32))
 #define HeapBaseOptions 1
+#elif defined(_AIX)
+// mmap adresses range start at 0x07000000_00000000 on AIX for 64 bits processes
+#define HeapBase(i) ((void*)(uintptr)(0x70ULL<<52))
+#define HeapBaseOptions 1
 #else
 #define HeapBase(i) ((void*)(uintptr)(i<<40|0x00c0ULL<<32))
 #define HeapBaseOptions 0x80
@@ -498,10 +502,15 @@ runtime_mallocinit(void)
 		// away from the running binary image and then round up
 		// to a MB boundary.
 
+#ifdef _AIX
+		// mmap adresses range start at 0x30000000 on AIX for 32 bits processes
+		end = 0x30000000U;
+#else
 		end = 0;
 		pend = &__go_end;
 		if(pend != nil)
 			end = *pend;
+#endif
 		p = (byte*)ROUND(end + (1<<18), 1<<20);
 		p_size = bitmap_size + spans_size + arena_size + PageSize;
 		p = runtime_SysReserve(p, p_size, &reserved);

libgo/runtime/mem.c

@@ -222,6 +222,12 @@ runtime_SysMap(void *v, uintptr n, bool reserved, uint64 *stat)
 		return;
 	}
 
+#ifdef _AIX
+	// AIX does not allow mapping a range that is already mapped.
+	// So always unmap first even if it is already unmapped.
+	runtime_munmap(v, n);
+#endif
+
 	p = runtime_mmap(v, n, PROT_READ|PROT_WRITE, MAP_ANON|MAP_FIXED|MAP_PRIVATE, fd, 0);
 	if(p == MAP_FAILED && errno == ENOMEM)
 		runtime_throw("runtime: out of memory");