[UBSAN] Common/x64Emitter.h: store to misaligned address (lines 364-366, 504)

[glebm]

When starting a game (I used GoW):

34:30:184 Core/MemMap.cpp:302 I[MEMMAP]: Memory system initialized. Base at 0x7f9700000000 (RAM at @ 0x7f9708000000, uncached @ 0x7f9748000000)
../Common/x64Emitter.h:365:46: runtime error: store to misaligned address 0x55faeed0002f for type 'u32', which requires 4 byte alignment
0x55faeed0002f: note: pointer points here
 0f 29 94 24 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00
             ^ 
../Common/x64Emitter.h:366:46: runtime error: store to misaligned address 0x55faedd0008e for type 'u64', which requires 8 byte alignment
0x55faedd0008e: note: pointer points here
 41 57 48 bb 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00
             ^ 
../Common/x64Emitter.cpp:504:26: runtime error: store to misaligned address 0x55faedd000d2 for type 's32', which requires 4 byte alignment
0x55faedd000d2: note: pointer points here
 eb 06  0f 88 00 00 00 00 41 8b  86 44 03 00 00 8b 44 03  00 8b d0 c1 ea 18 83 fa  68 75 0a 25 ff ff
              ^ 
34:30:185 Core/PSPLoaders.cpp:227 I[LOADER]: UCUS98737 : God of War®: Ghost of Sparta

Later during startup:

34:31:350 user_main    D[SCEKERNEL]: HLE/sceKernelMemory.cpp:658 277=sceKernelCreateFpl("radheap", partition=2, attr=00000000, bsize=19794176, nb=1)
34:31:350 user_main    D[HLE]: HLE/HLE.cpp:687 Compiling syscall to sceKernelAllocateFpl
34:31:350 user_main    D[SCEKERNEL]: HLE/sceKernelMemory.cpp:719 sceKernelAllocateFpl(277, 08c50540, 00000000)
../Common/x64Emitter.h:364:46: runtime error: store to misaligned address 0x55faedd20aad for type 'u16', which requires 2 byte alignment
0x55faedd20aad: note: pointer points here
 16 47 c5 08 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00
             ^ 

At a690127

[glebm]

This is a very low-priority issue because x64 supports unaligned access for non-SIMD operations, and the code there is unlikely to be auto-vectorized.

[hrydgard]

I don't even think I want to fix this, it's pretty much perfectly safe and slowing down the emitter is not something I'm interested in.

If you want to, you could make an ignore-file for UBSAN with this kind of stuff, I'd happily have that sitting around.

[glebm]

Well, with at least -O2 there is no difference between these 2 functions:

void Write1(u8 *out, u32 x) {
    *reinterpret_cast<u32*>(out) = x;
}

void Write2(u8 *out, u32 x) {
    out[0] = static_cast<u8>(x >> 0);
    out[1] = static_cast<u8>(x >> 8);
    out[2] = static_cast<u8>(x >> 16);
    out[3] = static_cast<u8>(x >> 24);
}

https://godbolt.org/z/afKd97

But fixing this would slow down debug builds

[glebm]

If we use memcpy instead for Write2, it is optimized even with -O0 https://godbolt.org/z/YbM9r6