Different behavior between x86_64 and ppc64le in overflow in locale_get_display_name

disclaimer.txt

When running the attached example in x86_64  and powerpc64le, different results are presented.

The attached file calls the function getDisplayName imported from libicu.

It is expected that in both architectures the program crashes in a core dump as pointed in [1] and
[2]. But in powerpc64le the last printed character is 247 and in x86_64 it is 255, i.e. in x86_64
the overflow happens 8 bytes ahead of ppc64le.

In order to compile the below code, the following command line is used:

  g++ test-libicu.cpp -o a.out -std=c++11 -licuuc
  
[1] https://github.com/facebook/hhvm/blob/master/hphp/runtime/ext/icu/ext_icu_locale.cpp#L223
[2] https://bugs.php.net/bug.php?id=67397

test-libicu.cpp

#include <unicode/ures.h>
#include <unicode/uloc.h>
#include <algorithm>
#include <utility>
#include <vector>


int main ()
{
	for (unsigned int i = 0; i < 260; i++)
	{
		printf("Locale size: %d\n", i);
		std::string locale_name("");
		
		for (unsigned int j = 0; j < i; j++)
		{
			locale_name.append("*");
		}
		
		std::string disp_locale("a");

		UErrorCode error = U_ZERO_ERROR;
		icu::UnicodeString buf;

		auto ubuf = buf.getBuffer(64);
		int32_t (*ulocfunc)(const char *loc, const char *dloc,
                      UChar *dest, int32_t destcap, UErrorCode *err);
		ulocfunc = uloc_getDisplayName;
		int32_t len = ulocfunc(locale_name.c_str(), disp_locale.c_str(), ubuf, buf.getCapacity(), &error);
	}

	return 0;

}

The final problem seems to be on the following line:
318 if (!uprv_strncmp(tableKey, "Languages", 9) && uprv_strtol(itemKey, NULL, 10)) {

reported in http://bugs.icu-project.org/trac/ticket/11936