[libc++abi] Fix test_exception_storage_nodynmem on MacOS

[smeenai]

Summary

Mach-O defaults to two-level namespaces, so calloc cannot be
interpositoned. Override it via the default malloc zone instead.

Note: DYLD_FORCE_FLAT_NAMESPACE can be used to enable interpositioning
on Mach-O, but calloc is used during library initialization, so
replacing it with a version which always returns NULL causes segfaults.
This could be worked around, but malloc zones are a cleaner solution.

[ikudrin]

This test is extremely fragile. Maybe, it is better to disable it, or even delete it altogether.

[smeenai]

In D26150#587973, @ikudrin wrote:

This test is extremely fragile. Maybe, it is better to disable it, or even delete it altogether.

I'll take your word for it, as the original author of the test, though I'm curious about where the fragility is coming in from :)

Are you planning to disable/delete, or should I?

[ikudrin]

The test is too implementation-specific, and trying to override a function like calloc makes it fragile. Unfortunately, I didn't find a better way to test the library's behavior in case of memory exhaustion, but now I believe that this test doesn't add any significant value. I'm going to remove it if no one objects.

[EricWF]

Go ahead and remove it. Ill try and fix it later next week when I get time.

[ikudrin]

Done: rL286337.

[smeenai]

Abandoning this then. In case the new incarnation of the test needs to overwrite any memory allocation methods, this diff has the most reliable way to do it on OS X :)

test/test_exception_storage_nodynmem.pass.cpp

 // cxa_exception_storage does not use dynamic memory in the single thread mode.
 // UNSUPPORTED: libcpp-has-no-threads
 
 // Our overwritten calloc() is not compatible with these sanitizers.
 // UNSUPPORTED: msan, tsan
 
 #include <assert.h>
 #include <cstdlib>
+#if defined(__APPLE__)
+#include <malloc/malloc.h>
+#endif
 
 static bool OverwrittenCallocCalled = false;
 
 // Override calloc to simulate exhaustion of dynamic memory
+#if !defined(__APPLE__)
 void *calloc(size_t, size_t) {
+#else
+void *calloc(malloc_zone_t *, size_t, size_t) {
+#endif
     OverwrittenCallocCalled = true;
     return 0;
 }
 
 int main(int argc, char *argv[]) {
+#if defined(__APPLE__)
+    malloc_zone_t *default_zone = malloc_default_zone();
+    default_zone->calloc = calloc;
+#endif
+
     // Run the test a couple of times
     // to ensure that fallback memory doesn't leak.
     for (int I = 0; I < 1000; ++I)
         try {
             throw 42;
         } catch (...) {
         }
 
     assert(OverwrittenCallocCalled);
     return 0;
 }