Re: New 64 bit Cygwin DLL

[Christopher Faylor <cgf-use-the-mailinglist-please at cygwin dot com>]

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.

cgf