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From: "Marc Nieper-Wißkirchen" <marc@nieper-wisskirchen.de>
To: Jeff Law <jeffreyalaw@gmail.com>
Cc: "David Malcolm" <dmalcolm@redhat.com>,
	gcc-patches@gcc.gnu.org,
	"Marc Nieper-Wißkirchen via Jit" <jit@gcc.gnu.org>
Subject: Re: [PATCH] gcc: pass-manager: Fix memory leak. [PR jit/63854]
Date: Fri, 11 Mar 2022 17:31:06 +0100	[thread overview]
Message-ID: <CAEYrNrSUdrgtxvu86h4tMNFDaq3yXgpLB0savw46_89nyy29wA@mail.gmail.com> (raw)
In-Reply-To: <CAEYrNrSRd9V=6pb_N4hyyiT14XV3CPzrzes32XceZHwT8zgi3g@mail.gmail.com>

Hi Jeff and David,

any news on this fix?

Thanks,

Marc

Am Mo., 31. Jan. 2022 um 12:42 Uhr schrieb Marc Nieper-Wißkirchen
<marc@nieper-wisskirchen.de>:
>
> Attached to this email is the patch updated to the recent renaming from *.c to *.cc.
>
>
> Am So., 23. Jan. 2022 um 14:18 Uhr schrieb Marc Nieper-Wißkirchen <marc@nieper-wisskirchen.de>:
>>
>> Am Sa., 15. Jan. 2022 um 14:56 Uhr schrieb 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.
>>
>> The only occurrences of m_name_to_pass_map are in pass-manager.h
>> (where it is defined as a private field of the class pass_manager) and
>> in passes.cc. There is just one instance where a name is added to the
>> map in passes.cc, namely through the put method. There, the name has
>> been xstrdup'ed.
>>
>> The name (as a const char *) escapes the pass map in
>> pass_manager::create_pass_tab through the call to
>> m_name_pass_map->traverse. This inserts the name into the pass_tab,
>> which is a static vec of const char *s. The pass_tab does not escape
>> the translation unit of passes.c. It is used in dump_one_pass where
>> the name is used as an argument to fprintf. The important point is
>> that it is not freed and not further copied.
>>
>> > >
>> > > If/once you're comfortable with the patch David, then go ahead and apply
>> > > it on Marc's behalf.
>> > >
>> > > jeff
>> > >

  reply	other threads:[~2022-03-11 16:31 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-19 21:30 Marc Nieper-Wißkirchen
2022-01-06 13:53 ` David Malcolm
2022-01-06 13:57   ` David Malcolm
2022-01-08  9:26     ` Marc Nieper-Wißkirchen
2022-01-08 10:07   ` Marc Nieper-Wißkirchen
2022-01-08 16:32   ` Jeff Law
2022-01-15 13:56     ` Marc Nieper-Wißkirchen
2022-01-23 13:18       ` Marc Nieper-Wißkirchen
2022-01-31 11:42         ` Marc Nieper-Wißkirchen
2022-03-11 16:31           ` Marc Nieper-Wißkirchen [this message]
2022-03-19 17:43           ` Jeff Law

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