[Xapian-devel] -D_FORTIFY_SOURCE (was Re: [Xapian-commits] 7903: trunk/xapian-core/)

[Richard Boulton]

Olly Betts wrote:
> It's hardly documented *well* in features.h either, at least in the
> version I have (glibc "2.4-1ubuntu12.3")!

Nor in mine - that was badly phrased: should have been something like 
"not documented well; a small amount of documentation is in features.h".

 > Sad really, it sounds like a
> promising idea, but if it's not advertised people just won't know to use
> it.

For the record, I came across it when reading this:
https://ols2006.108.redhat.com/reprints/jones-reprint.pdf

> There's perhaps a reason for that - the vast majority of the tests
> for __USE_FORTIFY_SOURCE (which is what _FORTIFY_SOURCE controls)
> in the glibc headers are followed by "&& !defined __cplusplus"!

Bah!  Well, I did manage to get an error out of it by breaking some of 
the code in flint, so it's not completely useless; hopefully C++ support 
will get better with time.

> It also doesn't activate at all unless you're using GCC >= 4.1
> so if your GCC is older, it'll have no effect at all on speed or
> fortification.

Ah, I couldn't find documentation on which GCC you needed for it, but I 
assumed it was fairly recent.

> The only thing which seems to actually be activated for C++ is some
> stuff to do with "__builtin_object_size", which seems to allow
> checking of the size of buffers known at compile time.  We don't make
> much use of static sized buffers, and we use snprintf where available,
> but it doesn't hurt to have extra checks if the overhead is small.
> 
> I prodded glibc CVS and found the vanilla glibc version this was first
> in, though it looks like RH backported this to older GCC (and possibly
> older glibc) for their distros.  I'll add that to the comment.

Cool.

-- 
Richard