Merge pull request #12250 from hrydgard/android-base-pointer-64-bit

Android: Get our base pointer in a saner way than YOLO, if possible.

Common/MemArenaAndroid.cpp

@@ -19,6 +19,7 @@
 
 #ifdef __ANDROID__
 
+#include "base/logging.h"
 #include "MemoryUtil.h"
 #include "MemArena.h"
 #include "StringUtils.h"
@@ -102,12 +103,28 @@ void MemArena::ReleaseView(void* view, size_t size) {
 
 u8* MemArena::Find4GBBase() {
 #if PPSSPP_ARCH(64BIT)
-	// Just grab some random 4GB...
-	return reinterpret_cast<u8*>(0x2300000000ULL);
+	// We should probably just go look in /proc/self/maps for some free space.
+	// But let's try the anonymous mmap trick, just like on 32-bit, but bigger and
+	// aligned to 4GB for the movk trick. We can ensure that we get an aligned 4GB
+	// address by grabbing 8GB and aligning the pointer.
+	const uint64_t EIGHT_GIGS = 0x200000000ULL;
+	void *base = mmap(0, EIGHT_GIGS, PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, -1, 0);
+	if (base) {
+		ILOG("base: %p", base);
+		uint64_t aligned_base = ((uint64_t)base + 0xFFFFFFFF) & ~0xFFFFFFFFULL;
+		ILOG("aligned_base: %p", (void *)aligned_base);
+		munmap(base, EIGHT_GIGS);
+		return reinterpret_cast<u8 *>(aligned_base);
+	} else {
+		u8 *hardcoded_ptr = reinterpret_cast<u8*>(0x2300000000ULL);
+		ILOG("Failed to anonymously map 8GB. Fall back to the hardcoded pointer %p.", hardcoded_ptr);
+		// Just grab some random 4GB...
+		// This has been known to fail lately though, see issue #12249.
+		return hardcoded_ptr;
+	}
 #else
 	// Address masking is used in 32-bit mode, so we can get away with less memory.
-	void* base = mmap(0, 0x10000000, PROT_READ | PROT_WRITE,
-		MAP_ANON | MAP_SHARED, -1, 0);
+	void* base = mmap(0, 0x10000000, PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, -1, 0);
 	if (base == MAP_FAILED) {
 		PanicAlert("Failed to map 256 MB of memory space: %s", strerror(errno));
 		return 0;