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Re: New 64 bit Cygwin DLL
- From: Corinna Vinschen <corinna-cygwin at cygwin dot com>
- To: cygwin-developers at cygwin dot com
- Date: Wed, 20 Mar 2013 10:58:46 +0100
- Subject: Re: New 64 bit Cygwin DLL
- References: <20130319094622 dot GL3003 at calimero dot vinschen dot de> <20130319160819 dot GA5336 at ednor dot casa dot cgf dot cx> <20130319162407 dot GC20727 at calimero dot vinschen dot de> <20130319162901 dot GA5808 at ednor dot casa dot cgf dot cx>
- Reply-to: cygwin-developers at cygwin dot com
On Mar 19 12:29, Christopher Faylor wrote:
> On Tue, Mar 19, 2013 at 05:24:07PM +0100, Corinna Vinschen wrote:
> >On Mar 19 12:08, Christopher Faylor wrote:
> >> On Tue, Mar 19, 2013 at 10:46:22AM +0100, Corinna Vinschen wrote:
> >> >Hi guys,
> >> >
> >> >
> >> >at long last, it looks like we found the real bug which was the reason
> >> >for the random crashes.
> >> >
> >> >There's a function sigdelayed, written in assembler, which is called
> >> >when a thread got a signal. Due to the way the function is called,
> >> >it turned out that it was missing two crucial features:
> >> >
> >> >- It can be called with any stack alignment, but on x86_64 it's important
> >> > that the stack is always 16 byte aligned when calling functions. So
> >> > sigdelayed had to make sure to align the stack before trundling along.
> >>
> >> >- sigdelayed only saved and restored the CPU registers which are
> >> > callee-saved in the Microsoft ABI, plus the registers used for the
> >> > return value of a function. Given how sigdelayed is called, this
> >> > was insufficient. The original, interrupted function needs the CPU
> >> > in its original state when sigdelayed returns to it, so sigdelayed
> >> > has to save and restore *all* registers.
> >>
> >> That's not really true for the 32-bit version. eax and ebx aren't
> >> normally saved around function calls but they are for sigdelayed.
> >
> >Yes, I saw that. And I thought it's necessary only for 32 bit due to
> >the different calling conventions, so I only saved the caller-saved and
> >return value registers on x86_64. So, in fact, this is entirely my own
> >fault.
> >
> >> It doesn't currently save floating point and debugging registers though.
> >
> >There may be situations in which it might be helpful to save and restore
> >the FP regs on 32 bit as well, though. For instance, printf is a SIGFE
> >function dealing with FP values.
>
> Right.
While we're at it, does i686 use the 387 FP regs or the xmms regs for FP?
I'm pretty fuzzy in this math stuff. I know that x86_64 uses the xmms
regs, but that's it...
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Maintainer cygwin AT cygwin DOT com
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