[Gc] cc under mac os x

[Boehm, Hans]

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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