Re: Build Error in master

[Noah Lavine]

Hello,

I inserted a GC_is_visible check in my code and learned that 'symbols'
is visible, but the things it points to were getting garbage collected
anyway. It seemed like a GC bug, so I'm trying to build Guile with the
latest version of GC and hoping that fixes it.

I just wanted to warn everyone that the GC_get_free_space_divisor
function will break with libgc 7.2alpha6, because libgc includes the
same function with the same name. I'm not sure what to do about that -
probably try to automatically discover it in configure and put more
#ifdefs around our definition (gc.c:212).

Noah

On Thu, Feb 2, 2012 at 9:59 PM, Noah Lavine <address@hidden> wrote:
> Got it! And unfortunately, it's a GC error. Here's what happens:
>
> symbols is an SCM object defined in symbols.c. It points to an
> scm_cell_t which has two elements: a type tag, and a pointer to an
> scm_weak_set_t. That scm_cell_t is at 0x10101cff0.
>
> However, that scm_cell_t is garbage collected in the scm_cons at
> symbols.c:250. The reason it gets filled with SCM_EOL is that the cons
> is scm_cons (SCM_BOOL_F, SCM_EOL). So I expect that the scm_cell_t is
> garbage collected and then immediately reclaimed to be the pair, which
> would result in its second cell being filled with SCM_EOL, which would
> explain why we later extract SCM_EOL from it.
>
> As a test, I changed the variable 'symbols' in symbols.c to be
> non-static. That didn't fix it, but then again, I don't really know
> how GC works yet.
>
> I can read the libgc documentation and try to figure this out, but can
> anyone point me to what I should be looking for?
>
> Thanks,
> Noah
>
> On Wed, Feb 1, 2012 at 4:01 AM, Andy Wingo <address@hidden> wrote:
>> On Wed 01 Feb 2012 03:12, Noah Lavine <address@hidden> writes:
>>
>>> In the failing call,
>>>   the SCM 'symbols' is 0x10101cff0, but the failing set is at 0x304,
>>> which has not been allocated.
>>
>> 0x304 is one of the iflags, SCM_EOL I think.
>>
>> So, I know it might not have anything to do with it, but can you verify
>> that your guile includes patch 0aed71aa51e89e714de2392c2a5f44694dca77ea
>> ?  I just committed that last night, and although it does not seem to be
>> related, who knows.
>>
>> Andy
>> --
>> http://wingolog.org/