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Re: Building a C++ program with -D__USE_MALLOC
- To: jbuck at synopsys dot com
- Subject: Re: Building a C++ program with -D__USE_MALLOC
- From: "Martin v. Loewis" <martin at mira dot isdn dot cs dot tu-berlin dot de>
- Date: Thu, 4 Nov 1999 00:55:10 +0100
- CC: yumf at ultimatech dot com, gcc at gcc dot gnu dot org, yumf at iago dot ultimatech dot com
- References: <199911032220.OAA26264@atrus.synopsys.com>
> You're missing the point, Martin. The default allocator does not call
> __builtin_new directly, rather, it uses __default_alloc_template,
> so that if it is used, some Purify errors (eg array-out-of-bounds) will
> be missed, since many allocations will share one malloc/new call.
Oh, I see. Thanks for pointing that out.
> It is really too bad that the default allocator gets wired in to the name
> mangling of the string type. One possibility that I haven't tried
> (which will break link compatibility, unfortunately), is to modify
> stl_alloc.h to make "alloc" a derived class, rather than a typedef.
> (This handling of the default allocator in libstdc++ v2 is nonstandard
It seems to me that setting __USE_MALLOC will break binary
compatibility, no matter how clever you attempt to do it.
For example, a std::vector instantiation now does not show the
allocator used in its mangled name, e.g.
_Vector_base<int, allocator<int> >::~_Vector_base(void)
This is the same whether __USE_MALLOC is defined or
not. Unfortunately, instantiating the vector results in an
_Vector_alloc_base<int, allocator<int>, true>::_M_deallocate(int *, unsigned int)
If __USE_MALLOC, then this in turn gives you
;simple_alloc<int, __malloc_alloc_template<0> >::deallocate(int *, unsigned int)
Otherwise, it is
;simple_alloc<int, __default_alloc_template<true, 0> >::deallocate(int *, unsigned int)
This is not surprising, because there is no polymorphism here - hence
no chance to replace things at run time.
I could hope for two different solutions: On the one hand, Purify may
be able to learn about standard allocators. I believe it is quite
flexible in recognizing memory allocation functions, although I have
not tried adding some.
On the other hand, you would recompile everything with __USE_MALLOC -
perhaps that could be simplified with another multilib variant
(although a separate compiler installation would probably be easier).