Layout of VM Internals

Interpreter Frame

This layout is also marshaled as struct cframe.

Offset	VARIABLE (64 bits by default)
+0x78	SAVE_RET
+0x70	SAVE_RBP
+0x68	SAVE_RBX
+0x60	SAVE_R15
+0x58	SAVE_R14
+0x50	SAVE_CFRAME
+0x48	SAVE_PC
+0x40	SAVE_L
+0x38	SAVE_ERRF
+0x30	SAVE_NRES
+0x2c	MULTRES (uint32_t)
+0x28	SAVE_VMSTATE (int32_t)
+0x20	TMPTV_TAG
+0x18	TMPTV
+0x10	TMPa2
+0x08	TMPa
+0x04	TMP2 (uint32_t)
$rsp	TMP1 (uint32_t)

Register Mapping

Host Register	Host Callee-saved?	VM State Register	VM Op / Aux Register	VM C Argument Register
%rax	NO		RCa, RDa	CRET
%rbx	YES	PC
%rcx	NO		RAa	CARG4
%rdx	NO			CARG3
%rbp	YES	OP	RBa
%rsp	YES
%rsi	NO			CARG2
%rdi	NO			CARG1
%r8	NO		AUX2	CARG5
%r9	NO		AUX1	CARG6
%r10	NO	BASE
%r11	NO		XCHG
%r12	YES
%r13	YES
%r14	YES	DISPATCH
%r15	YES	KBASE
%xmm0	NO			CARG1f

Notes:

• Internal VM op registers RA, RB and RC (aliased with RD) correspond to 32-bit host registers %ecx, %ebp and %eax, respectively.
• 32-bit registers for C arguments are denoted as CARG*d and correspond to the same host registers as their 64-bit versions.