Re: [PATCH] gcc: pass-manager: Fix memory leak. [PR jit/63854]

["Marc Nieper-Wißkirchen" <marc@nieper-wisskirchen.de>]

Jeff, David, do you need any more input from my side?

-- Marc

Am Sa., 8. Jan. 2022 um 17:32 Uhr schrieb Jeff Law <jeffreyalaw@gmail.com>:
>
>
>
> On 1/6/2022 6:53 AM, David Malcolm via Gcc-patches wrote:
> > On Sun, 2021-12-19 at 22:30 +0100, Marc Nieper-Wißkirchen wrote:
> >> This patch fixes a memory leak in the pass manager. In the existing
> >> code,
> >> the m_name_to_pass_map is allocated in
> >> pass_manager::register_pass_name, but
> >> never deallocated.  This is fixed by adding a deletion in
> >> pass_manager::~pass_manager.  Moreover the string keys in
> >> m_name_to_pass_map are
> >> all dynamically allocated.  To free them, this patch adds a new hash
> >> trait for
> >> string hashes that are to be freed when the corresponding hash entry
> >> is removed.
> >>
> >> This fix is particularly relevant for using GCC as a library through
> >> libgccjit.
> >> The memory leak also occurs when libgccjit is instructed to use an
> >> external
> >> driver.
> >>
> >> Before the patch, compiling the hello world example of libgccjit with
> >> the external driver under Valgrind shows a loss of 12,611 (48 direct)
> >> bytes.  After the patch, no memory leaks are reported anymore.
> >> (Memory leaks occurring when using the internal driver are mostly in
> >> the driver code in gcc/gcc.c and have to be fixed separately.)
> >>
> >> The patch has been tested by fully bootstrapping the compiler with
> >> the
> >> frontends C, C++, Fortran, LTO, ObjC, JIT and running the test suite
> >> under a x86_64-pc-linux-gnu host.
> > Thanks for the patch.
> >
> > It looks correct to me, given that pass_manager::register_pass_name
> > does an xstrdup and puts the result in the map.
> >
> > That said:
> > - I'm not officially a reviewer for this part of gcc (though I probably
> > touched this code last)
> > - is it cleaner to instead change m_name_to_pass_map's key type from
> > const char * to char *, to convey that the map "owns" the name?  That
> > way we probably wouldn't need struct typed_const_free_remove, and (I
> > hope) works better with the type system.
> >
> > Dave
> >
> >> gcc/ChangeLog:
> >>
> >>          PR jit/63854
> >>          * hash-traits.h (struct typed_const_free_remove): New.
> >>          (struct free_string_hash): New.
> >>          * pass_manager.h: Use free_string_hash.
> >>          * passes.c (pass_manager::register_pass_name): Use
> >> free_string_hash.
> >>          (pass_manager::~pass_manager): Delete allocated
> >> m_name_to_pass_map.
> My concern (and what I hadn't had time to dig into) was we initially
> used nofree_string_hash -- I wanted to make sure there wasn't any path
> where the name came from the stack (can't be free'd), was saved
> elsewhere (danging pointer) and the like.  ie, why were we using
> nofree_string_hash to begin with?  I've never really mucked around with
> these bits, so the analysis side kept falling off the daily todo list.
>
> If/once you're comfortable with the patch David, then go ahead and apply
> it on Marc's behalf.
>
> jeff
>