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Date: Fri, 27 Jun 2025 10:45:16 -0700 (PDT)
X-X-Sender: jeremyd AT resin DOT csoft DOT net
To: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
cc: Pip Cet <pipcet AT protonmail DOT com>
Subject: Re: XSAVE-related segfaults observed under wine
In-Reply-To: <aF60VympSWbCeu2n@calimero.vinschen.de>
Message-ID: <abda5210-ba7f-a4a0-5c0c-880367fec254@jdrake.com>
References: <87bjq9457k DOT fsf AT protonmail DOT com>
 <aF60VympSWbCeu2n AT calimero DOT vinschen DOT de>
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From: Jeremy Drake via Cygwin <cygwin AT cygwin DOT com>
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On Fri, 27 Jun 2025, Corinna Vinschen via Cygwin wrote:

> Hi Pip,
>
> On Jun 27 14:41, Pip Cet via Cygwin wrote:
> > My suggested fix is to align the value in %rbx to the next 64-byte
> > multiple after the "cpuid" instruction is executed, by performing the
> > assembler equivalent of $rbx += 63; $rbx &= -64; I tried this:
> >
> > diff --git a/winsup/cygwin/scripts/gendef b/winsup/cygwin/scripts/gendef
> > index 861a2405b..d681fde3f 100755
> > --- a/winsup/cygwin/scripts/gendef
> > +++ b/winsup/cygwin/scripts/gendef
> > @@ -232,6 +232,8 @@ sigdelayed:
> >  	movl	\$0x0d,%eax
> >  	xorl	%ecx,%ecx
> >  	cpuid	# get necessary space for xsave
> > +	addq	\$63, %rbx
> > +	andq	\$-64, %rbx # align to next 64-byte multiple
>
> what about a oneliner instead by just aligning rsp?  As in
>
> >  	movq	%rbx,%rcx
> >  	addq	\$0x48,%rbx # 0x18 for alignment, 0x30 for additional space

If aligning via andq, does the 0x18 "for alignment" still need to be
included?

> >  	subq	%rbx,%rsp
>
>   +     andq    \$-64, %rsp
>

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