[PATCH v4] x86-64: Allocate state buffer space for RDI, RSI and RBX
Florian Weimer
fweimer@redhat.com
Mon Mar 18 10:22:47 GMT 2024
* H. J. Lu:
> _dl_tlsdesc_dynamic preserves RDI, RSI and RBX before realigning stack.
> After realigning stack, it saves RCX, RDX, R8, R9, R10 and R11. Define
> TLSDESC_CALL_REGISTER_SAVE_AREA to allocate space for RDI, RSI and RBX
> to avoid clobbering saved RDI, RSI and RBX values on stack by xsave to
> STATE_SAVE_OFFSET(%rsp).
>
> +==================+<- stack frame start aligned at 8 or 16 bytes
It's 8-byte aligned only? If the caller uses the psABI convention, we
have %rsp ≡ 8 (mod 16).
> | |<- RDI
> | |<- RSI
> | |<- RBX
I would add something like “originally in the red zone” here.
> | |<- paddings from stack realignment of 64 bytes
> |------------------|<- xsave buffer end aligned at 64 bytes
> | |<-
> | |<-
> | |<-
> |------------------|<- xsave buffer start at STATE_SAVE_OFFSET(%rsp)
> | |<- 8-byte padding
Maybe add “to achieve 64-bit alignment”.
> | |<- 8-byte padding
> | |<- R11
> | |<- R10
> | |<- R9
> | |<- R8
> | |<- RDX
> | |<- RCX
> +==================+<- State buffer start aligned at 64 bytes
Isn't this “%rsp aligned at 64 bytes”?
Likewise for the comment in the sources below.
> diff --git a/sysdeps/x86/sysdep.h b/sysdeps/x86/sysdep.h
> index db8e576e91..46fcd27345 100644
> --- a/sysdeps/x86/sysdep.h
> +++ b/sysdeps/x86/sysdep.h
> @@ -46,6 +46,34 @@
> red-zone into account. */
> # define STATE_SAVE_OFFSET (8 * 7 + 8)
The comment on STATE_SAVE_OFFSET needs updating, too.
I would like to see comments from Noah or Sunil. You'll have to
maintain this, too. 8-)
I find the macro consts rather confusing, but maybe that's just me.
Thanks,
Florian
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