[Gc] cc under mac os x

Grayson, Daniel R. dan at math.uiuc.edu
Mon Jul 30 17:31:04 PDT 2012


That works (with Apple clang version 4.0).

On Jul 30, 2012, at 8:25 PM, "Boehm, Hans" <hans.boehm at hp.com> wrote:

> Maybe we should just call GC_approx_sp() instead of taking the address of dummy?  This is all very heuristic, so being off by a few bytes here shouldn't matter.
> 
> Hans
> 
>> -----Original Message-----
>> From: Grayson, Daniel R. [mailto:dan at math.uiuc.edu]
>> Sent: Monday, July 30, 2012 4:48 PM
>> To: Boehm, Hans
>> Cc: gc at linux.hpl.hp.com
>> Subject: Re: [Gc] cc under mac os x
>> 
>> The problem is that the comparison
>> 
>> 	(word)(&dummy[0]) > (word)limit
>> 
>> in GC_clear_stack_inner is optimized by -O2 to the constant value FALSE
>> (1).  Same
>> for any comparison of those two pointers.  The only solution I see is
>> to
>> pass &dummy[0] through an identity function compiled in another file,
>> so the
>> optimizer can't see it.  That works.
>> 
>> On Jul 30, 2012, at 5:56 PM, "Boehm, Hans" <hans.boehm at hp.com> wrote:
>> 
>>> Note that GC_clear_stack_inner() is a tiny piece of non-portable
>> code.  It would be nice to understand why this is failing.
>>> 
>>> I don't understand the limit value.  It's computed in GC_clear_stack
>> from GC_approx_sp(), which should return the stack pointer.  It should
>> be a few K less than the stack pointer.  It doesn't look like it.
>> Stepping through GC_clear_stack() the first time it's called might be
>> helpful.
>>> 
>>> This is also code that can break with excessively clever whole
>> program analysis.  It recourses until the stack pointer is below a
>> certain value.  If the compiler manages to recognize that the function
>> is tail recursive (which we intentionally make hard), the stack may not
>> actually grow as a result of the recursion, causing this to loop
>> forever.
>>> 
>>> Stubbing out GC_clear_stack_inner() completely (just return arg)
>> should only introduce a performance issue.  That may also be worth
>> trying.
>>> 
>>> Hans
>>> 
>>>> -----Original Message-----
>>>> From: gc-bounces at linux.hpl.hp.com [mailto:gc-
>> bounces at linux.hpl.hp.com]
>>>> On Behalf Of Grayson, Daniel R.
>>>> Sent: Sunday, July 29, 2012 11:59 AM
>>>> To: gc at linux.hpl.hp.com
>>>> Subject: [Gc] cc under mac os x
>>>> 
>>>> I discovered today that libgc doesn't work with /usr/bin/cc under
>>>> Mac OS X 10.8.  I usually use gcc, so having it work with cc is not
>>>> important to me, but it might be to others.
>>>> 
>>>> Most of the tests fail with a segmentation fault.  Gdb shows a deep
>>>> recursion:
>>>> 
>>>> #0  0x0000000100011086 in GC_clear_stack_inner (arg=0x0,
>>>> limit=0x7fff5fbfa0a0 "") at misc.c:306
>>>> #1  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #2  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #3  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #4  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #5  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #6  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #7  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #8  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #9  0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #10 0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> #11 0x0000000100011096 in GC_clear_stack_inner (arg=0x0, limit=0x6a8
>>>> <Address 0x6a8 out of bounds>) at misc.c:308
>>>> 
>>>> 
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> 




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