[Tarantool-patches] [PATCH luajit v1 05/11] vm: introduce LFUNC and FFUNC vmstates

[Sergey Kaplun]

Hi, Sergos!

Thanks for the review!

On 25.12.20, Sergey Ostanevich wrote:
> Hi!
> 
> Thanks for the patch! 
> Some comments below.
> 
> <...>
> > diff --git a/src/vm_x64.dasc b/src/vm_x64.dasc
> > index 80753e0..d4d3a1d 100644
> > --- a/src/vm_x64.dasc
> > +++ b/src/vm_x64.dasc
> > @@ -140,7 +140,7 @@
> > |//-----------------------------------------------------------------------
> > |.else			// x64/POSIX stack layout
> > |
> > -|.define CFRAME_SPACE,	aword*5			// Delta for rsp (see <--).
> > +|.define CFRAME_SPACE,	qword*7			// Delta for rsp (see <--).
> > |.macro saveregs_
> > |  push rbx; push r15; push r14
> > |.if NO_UNWIND
> > @@ -161,26 +161,29 @@
> > |
> > |//----- 16 byte aligned,
> > |.if NO_UNWIND
> > -|.define SAVE_RET,	aword [rsp+aword*11]	//<-- rsp entering interpreter.
> > -|.define SAVE_R4,	aword [rsp+aword*10]
> > -|.define SAVE_R3,	aword [rsp+aword*9]
> > -|.define SAVE_R2,	aword [rsp+aword*8]
> > -|.define SAVE_R1,	aword [rsp+aword*7]
> > -|.define SAVE_RU2,	aword [rsp+aword*6]
> > -|.define SAVE_RU1,	aword [rsp+aword*5]	//<-- rsp after register saves.
> 
> Why did you change all ‘aword’ - which represents address, AFAIU into a qword?

According unofficial dynasm documentation [1] `aword` equals 4 or 8
bytes on x86 and x64 correspondingly. Each of this `aword` usage is
already inside defined x86 or x64 arch. So aword usage is misleading
here -- there is always one case, how it can be represented. I've
already changed this code chunk so I thought that is nothing bad to
rewrite it in a more clear way. I can drop these changes if you and Igor
insist on it.

> 
> > +|.define SAVE_RET,	qword [rsp+qword*13]	//<-- rsp entering interpreter.
> > +|.define SAVE_R4,	qword [rsp+qword*12]
> > +|.define SAVE_R3,	qword [rsp+qword*11]
> > +|.define SAVE_R2,	qword [rsp+qword*10]
> > +|.define SAVE_R1,	qword [rsp+qword*9]
> > +|.define SAVE_RU2,	qword [rsp+qword*8]
> > +|.define SAVE_RU1,	qword [rsp+qword*7]	//<-- rsp after register saves.
> > |.else
> > -|.define SAVE_RET,	aword [rsp+aword*9]	//<-- rsp entering interpreter.
> > -|.define SAVE_R4,	aword [rsp+aword*8]
> > -|.define SAVE_R3,	aword [rsp+aword*7]
> > -|.define SAVE_R2,	aword [rsp+aword*6]
> > -|.define SAVE_R1,	aword [rsp+aword*5]	//<-- rsp after register saves.
> > +|.define SAVE_RET,	qword [rsp+qword*11]	//<-- rsp entering interpreter.
> > +|.define SAVE_R4,	qword [rsp+qword*10]
> > +|.define SAVE_R3,	qword [rsp+qword*9]
> > +|.define SAVE_R2,	qword [rsp+qword*8]
> > +|.define SAVE_R1,	qword [rsp+qword*7]	//<-- rsp after register saves.
> > |.endif
> > -|.define SAVE_CFRAME,	aword [rsp+aword*4]
> > -|.define SAVE_PC,	aword [rsp+aword*3]
> > -|.define SAVE_L,	aword [rsp+aword*2]
> > +|.define SAVE_CFRAME,	qword [rsp+qword*6]
> > +|.define SAVE_UNUSED2,	qword [rsp+qword*5]
> 
> The naming is quite boggling: to save something unused? Why?

Will rewrite it as UNUSED only, thanks.

> 
> > +|.define SAVE_UNUSED1,	dword [rsp+dword*8]
> > +|.define SAVE_VMSTATE,	dword [rsp+dword*8]
> > +|.define SAVE_PC,	qword [rsp+qword*3]
> > +|.define SAVE_L,	qword [rsp+qword*2]
> > |.define SAVE_ERRF,	dword [rsp+dword*3]
> > |.define SAVE_NRES,	dword [rsp+dword*2]
> > -|.define TMP1,		aword [rsp]		//<-- rsp while in interpreter.
> > +|.define TMP1,		qword [rsp]		//<-- rsp while in interpreter.
> > |//----- 16 byte aligned
> > |
> > |.define TMP1d,		dword [rsp]
> > @@ -342,6 +345,20 @@
> > |  mov dword [DISPATCH+DISPATCH_GL(vmstate)], ~LJ_VMST_..st
> > |.endmacro
> > |
> 
> Can you set an empty versions of the macros for WIN, so that
> later at uses do not do not wrap with .if—--.endif?

Good idea. Thank you!

> 
> > +|.if not WIN
> > +|// Save vmstate through register.
> > +|.macro save_vmstate_through, reg
> > +|  mov reg, dword [DISPATCH+DISPATCH_GL(vmstate)]
> > +|  mov SAVE_VMSTATE, reg
> > +|.endmacro
> > +|
> > +|// Restore vmstate through register.
> > +|.macro restore_vmstate_through, reg
> > +|  mov reg, SAVE_VMSTATE
> > +|  mov dword [DISPATCH+DISPATCH_GL(vmstate)], reg
> > +|.endmacro
> > +|.endif // WIN
> > +|
> > |.macro fpop1; fstp st1; .endmacro
> 

[1]: https://corsix.github.io/dynasm-doc/instructions.html#memory

-- 
Best regards,
Sergey Kaplun