[libiberty] xmalloc cannot return NULL

[libiberty] xmalloc cannot return NULL

[Marc Glisse]

Hello,

libiberty provides a function xmalloc that never returns NULL. However, 
there are some hints that it might be ok if someone wants to supply their 
own xmalloc that can return NULL (though that would break a lot of things, 
including in libiberty itself).

I would like to remove that freedom, and the point of this email (I hope 
it doesn't bounce from too many of these addresses) is to ask all 
libiberty users if that would cause problems for them. I already heard 
from gcc and gdb that they are happy forbidding a null return value from 
xmalloc.

Why do I want to do that? I just added an attribute "returns_nonnull" to 
gcc and would like to mark relevant functions, to let the compiler 
optimize based on this property.

http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00817.html

-- 
Marc Glisse

Re: [libiberty] xmalloc cannot return NULL

[Mike Frysinger]

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On Monday 14 October 2013 13:59:16 Marc Glisse wrote:
> libiberty provides a function xmalloc that never returns NULL. However,
> there are some hints that it might be ok if someone wants to supply their
> own xmalloc that can return NULL (though that would break a lot of things,
> including in libiberty itself).
> 
> I would like to remove that freedom, and the point of this email (I hope
> it doesn't bounce from too many of these addresses) is to ask all
> libiberty users if that would cause problems for them. I already heard
> from gcc and gdb that they are happy forbidding a null return value from
> xmalloc.
> 
> Why do I want to do that? I just added an attribute "returns_nonnull" to
> gcc and would like to mark relevant functions, to let the compiler
> optimize based on this property.
> 
> http://gcc.gnu.org/ml/gcc-patches/2013-10/msg00817.html

makes sense to me.  as you point out, we write code based on the assumption 
that NULL is never returned (although, perhaps phrased more accurately, that 
the pointer returned is always valid).
-mike

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