Re: [PATCH v2] x86-64: Allocate state buffer space for RDI, RSI and RBX

[Florian Weimer <fweimer@redhat.com>]

* H. J. Lu:

> diff --git a/sysdeps/x86/sysdep.h b/sysdeps/x86/sysdep.h
> index db8e576e91..262d4083e2 100644
> --- a/sysdeps/x86/sysdep.h
> +++ b/sysdeps/x86/sysdep.h
> @@ -46,6 +46,13 @@
>     red-zone into account.  */
>  # define STATE_SAVE_OFFSET (8 * 7 + 8)
>  
> +/* _dl_tlsdesc_dynamic preserves RDI, RSI and RBX before realigning
> +   stack.  After realigning stack, it saves RCX, RDX, R8, R9, R10 and
> +   R11.  Allocate space for all integer registers and round up the state
> +   size to 64 bytes to avoid clobbering saved RDI, RSI and RBX values on
> +   stack by xsave on STATE_SAVE_OFFSET(%rsp).  */
> +# define TLSDESC_CALL_STATE_SAVE_OFFSET (STATE_SAVE_OFFSET + 64)

Why 64?  The red zone is 128 bytes, and the three registers only need 24
bytes.  I think 24 has to be rounded up to 64 to preserve the XSAVE area
alignment.

The macro is also misnamed because it is not an offset.  The real offset
depends on what the stack realignment did.

Thanks,
Florian