Subject: Re: Segfault while building on 64-bit Cygwin

From: Charles Stanhope <[email-masked]>
Date: Sun, 16 Feb 2020 17:08:25 -0800

On 2/16/20, Mike Gran <[email-masked]> wrote:
> On Fri, Feb 14, 2020 at 09:46:04AM -0800, Charles Stanhope wrote:
>> Andy, I don't know if you'd want to continue this here or on
>> lightening's gitlab page, but I looked into this a little bit a few
>> minutes here and there this past weeek. The x86 "fast-call" calling
>> convention used on Windows x64[0] and shared by Cygwin[1] requires
>> that the caller reserve 32 bytes of memory on the stack for the callee
>> to spill the register parameters (even if the callee takes fewer than
>> four parameters). I think lightening is currently missing that for the
>> x64 case for Cygwin.
>>
>> To test the idea, I made a small modification (patch attached) that is
>> *not* intended as a solution as it doesn't work for the general case,
>> but it does allow the tests to pass on Cygwin 64.
>
> I can confirm that Charles's patch, plus another one line patch
> to define CPU_SETSIZE, is enough to get Guile 3.0.x to build and run
> on my box.  All tests pass except strptime in French, and the absence
> of crypt.  This is a 64-bit build.

Mike, thanks for going further with the Guile build. The CPU_SETSIZE
issue was what was hanging me up from compiling before Andy's comment
got me to look at lightening. I assumed I had some configuration,
package, or compiler issue. Good to know there's a simple fix.

Just a further warning to anyone watching, that patch I posted is a
real hack job just to test my theory of the cause of the segfault. I
would expect it to fail when you have fewer than four arguments in a
JITed function call. I wouldn't try doing much else with that Guile
build besides run the tests. :)

--
Charles