Bug in __register_exitproc() in __atexit.c
Sun Dec 13 14:43:00 GMT 2015
On Wednesday 09 of December 2015 10:27:31 Corinna Vinschen wrote:
> On Dec 8 16:40, Freddie Chopin wrote:
> > Hello!
> > Today I noticed that even when I disable dynamic allocation of memory in
> > atexit (with --disable-newlib-atexit-dynamic-alloc switch) malloc() is
> > used in __register_exitproc().
> > First of all, if this switch is used, then _ATEXIT_DYNAMIC_ALLOC is not
> > defined, so the first use of malloc() in this function - at line 93 - is
> > indeed disabled. But if small reent is used, malloc() is used again at
> > line
> > 120 - this time it's not conditional on _ATEXIT_DYNAMIC_ALLOC being
> > defined.
> > Moreover, at first glance it seems that there's a bug in this function.
> > The
> > __atexit_lock lock is acquired at entry, but there are at two places where
> > it is not released before return - at line 86 and at line 91.
> > Should I try to provide a patch for both issues?
> That would be nice :)
OK, I've just sent the patches.
I've checked that newlib still compiles with all 8 combinations of related
options (reent small, global atexit, dynamic atexit). The fix I implemented
also solves the issue I had - __register_exitproc() no longer uses malloc() if
--disable-newlib-atexit-dynamic-alloc was used.
The first patch - the one for missing lock releases - is trivial and there's
not much to debate.
The second one - with the fix for dynamic atexit allocation - is more
problematic... It turns out that when both --disable-newlib-atexit-dynamic-
alloc and --enable-newlib-reent-small are used, then __register_exitproc()
called by on_exit() or __cxa_atexit() will never succeed. Both of these
variants pass an argument to the registered function and this argument is
placed in a struct that is _NOT_ part of _atexit struct.
This can actually be solved easily - you'd just need to allocate a static
instance of _on_exit_args struct and use it for the first 32 registered
functions. The only problem is that the size of this struct is - for 32-bit
ARM - 264 bytes, so not exactly "small". So I was wondering what approach
would you suggest? Leave it as it is (with the fix) or maybe add static
instance of this struct when dynamic allocation is disabled for atexit-like
Maybe it would be possible to have the instance of this struct as a weak
reference and pull it in only if on_exit() or __cxa_atexit() are used?
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