test: specialize OOM check for AIX

Assumption that if memory can be malloc()ed it can be used is not true
on AIX. Later access of the allocated pages can trigger SIGKILL if there
are insufficient VM pages.

Use psdanger() to better estimate available memory.

Fixes: nodejs/build#1849

More info:
- https://www.ibm.com/support/knowledgecenter/en/ssw_aix_71/generalprogramming/sys_mem_alloc.html
- https://www.ibm.com/support/knowledgecenter/en/ssw_aix_71/p_bostechref/psdanger.html

Related to:
- nodejs/build#1820 (comment)
- nodejs#28469
- nodejs#28516

test/addons/addon.status

@@ -3,17 +3,3 @@ prefix addons
 [true] # This section applies to all platforms
 
 [$system==aix]
-# https://github.com/nodejs/build/issues/1820#issuecomment-505998851
-# https://github.com/nodejs/node/pull/28469
-# https://github.com/nodejs/node/pull/28516
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max.js: SKIP
-
-# https://github.com/nodejs/node/pull/28516
-stringbytes-external-exceed-max/test-stringbytes-external-at-max: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-ascii: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-base64: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-binary: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-hex: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-1-utf8: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max-by-2: SKIP
-stringbytes-external-exceed-max/test-stringbytes-external-exceed-max: SKIP

test/addons/stringbytes-external-exceed-max/binding.cc

@@ -2,12 +2,42 @@
 #include <node.h>
 #include <v8.h>
 
+#ifdef _AIX
+// AIX allows over-allocation, and will SIGKILL when the allocated pages are
+// used if there is not enough VM. Check for available space until
+// out-of-memory.  Don't allow more then some (large) proportion of it to be
+// used for the test strings, so Node & V8 have some space for allocations.
+#include <signal.h>
+#include <sys/vminfo.h>
+
+static void* Allowed(size_t size) {
+  blkcnt_t allowedBlocks = psdanger(SIGKILL);
+
+  if (allowedBlocks < 1) {
+    // Already OOM
+    return nullptr;
+  }
+  const size_t BYTES_PER_BLOCK = 512;
+  size_t allowed = (allowedBlocks * BYTES_PER_BLOCK * 4) / 5;
+  if (size < allowed) {
+    return malloc(size);
+  }
+  return nullptr;
+}
+#else
+// Other systems also allow over-allocation, but this malloc-and-free approach
+// seems to be working for them.
+static void* Allowed(size_t size) {
+  return malloc(size);
+}
+#endif  // _AIX
+
 void EnsureAllocation(const v8::FunctionCallbackInfo<v8::Value> &args) {
   v8::Isolate* isolate = args.GetIsolate();
   uintptr_t size = args[0].As<v8::Integer>()->Value();
   v8::Local<v8::Boolean> success;
 
-  void* buffer = malloc(size);
+  void* buffer = Allowed(size);
   if (buffer) {
     success = v8::Boolean::New(isolate, true);
     free(buffer);