arm64: fixes around icache flushing

Source/Core/Common/Arm64Emitter.cpp

@@ -329,11 +329,32 @@ void ARM64XEmitter::FlushIcacheSection(u8* start, u8* end)
   // Header file says this is equivalent to: sys_icache_invalidate(start, end - start);
   sys_cache_control(kCacheFunctionPrepareForExecution, start, end - start);
 #else
-#ifdef __clang__
-  __clear_cache(start, end);
-#else
-  __builtin___clear_cache(start, end);
-#endif
+  // Don't rely on GCC's __clear_cache implementation, as it caches
+  // icache/dcache cache line sizes, that can vary between cores on
+  // big.LITTLE architectures.
+  u64 addr, ctr_el0;
+  static size_t icache_line_size = 0xffff, dcache_line_size = 0xffff;
+  size_t isize, dsize;
+
+  __asm__ volatile("mrs %0, ctr_el0" : "=r"(ctr_el0));
+  isize = 4 << ((ctr_el0 >> 0) & 0xf);
+  dsize = 4 << ((ctr_el0 >> 16) & 0xf);
+
+  // use the global minimum cache line size
+  icache_line_size = isize = icache_line_size < isize ? icache_line_size : isize;
+  dcache_line_size = dsize = dcache_line_size < dsize ? dcache_line_size : dsize;
+
+  addr = (u64)start & ~(u64)(dsize - 1);
+  for (; addr < (u64)end; addr += dsize)
+    __asm__ volatile("dc civac, %0" : : "r"(addr) : "memory");
+  __asm__ volatile("dsb ish" : : : "memory");
+
+  addr = (u64)start & ~(u64)(isize - 1);
+  for (; addr < (u64)end; addr += isize)
+    __asm__ volatile("ic ivau, %0" : : "r"(addr) : "memory");
+
+  __asm__ volatile("dsb ish" : : : "memory");
+  __asm__ volatile("isb" : : : "memory");
 #endif
 }