[9] RFR(S): 8148490: RegisterSaver::restore_live_registers() fails to restore xmm registers on 32 bit

Tobias Hartmann tobias.hartmann at oracle.com
Fri Jan 29 14:16:22 UTC 2016


please review the following patch:

RegisterSaver::save_live_registers() and RegisterSaver::restore_live_registers() are used by the safepoint handling code to save and restore registers. The following code is emitted to save and restore XMM/YMM registers on 32 bit: 

   0xf34ca12e:	vmovdqu %xmm0,0xb0(%esp)
   0xf34ca137:	vmovdqu %xmm1,0xc0(%esp)
   0xf34ca16d:	vmovdqu %xmm7,0x120(%esp)
   0xf34ca176:	sub    $0x80,%esp
   0xf34ca17c:	vextractf128 $0x1,%ymm0,(%esp)
   0xf34ca183:	vextractf128 $0x1,%ymm1,0x10(%esp)
   0xf34ca1b3:	vextractf128 $0x1,%ymm7,0x70(%esp)

   0xf34ca202:	vinsertf128 $0x1,(%esp),%ymm0,%ymm0
   0xf34ca209:	vinsertf128 $0x1,0x10(%esp),%ymm1,%ymm1
   0xf34ca239:	vinsertf128 $0x1,0x70(%esp),%ymm7,%ymm7
   0xf34ca241:	add    $0x80,%esp
   0xf34ca247:	vmovdqu 0x130(%esp),%xmm0
   0xf34ca250:	vmovdqu 0x140(%esp),%xmm1
   0xf34ca286:	vmovdqu 0x1a0(%esp),%xmm7

The stack offsets for the vmovdqu instructions are wrong, causing the XMM registers to contain random values after a safepoint. The problem is that "additional_frame_bytes" is added to the stack offset although the stack pointer is incremented just before:

283     __ addptr(rsp, additional_frame_bytes); // Save upper half of YMM registers

The regression test fails with "Test failed: array[0] = 1973.0 but should be 10.000" because the vectorized loop returns a wrong result.

I spotted and fixed the following other problems:
- the vmovdqu instructions should be emitted before restoring YMM and ZMM because they zero the upper part of the XMM registers (i.e. YMM/ZMM)
- if 'UseAVX > 2' is set/available, we save the ZMM registers as well but we do not increment 'additional_frame_words' accordingly (we need another 8*32 bytes of stack space) 

Unfortunately, I don't have access to a CPU with the AVX-512 instruction set to test the "UseAVX > 2" related changes. Michael, could you verify the changes?

The problems were introduced by the fix for JDK-8142980.


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