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Re: New 64 bit Cygwin DLL
- From: Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>
- To: cygwin-developers at cygwin dot com
- Date: Tue, 19 Mar 2013 12:08:19 -0400
- Subject: Re: New 64 bit Cygwin DLL
- References: <20130319094622 dot GL3003 at calimero dot vinschen dot de>
- Reply-to: cygwin-developers at cygwin dot com
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. It
doesn't currently save floating point and debugging registers though.
I thought I mentioned when you asked what could be causing these
random problems that it was likely to be related to signals. I
guess I just thought it though since I can't find the email which
I thought I sent suggesting it. Sorry.
cgf