Squashed commit of the following:

commit 2d7d545c4c4bfce7fdcbcbe9baaeb437915742f0
Merge: 625a1249 b178914b
Author: Yukihiro "Matz" Matsumoto <[email protected]>
Date:   Fri Jun 5 14:35:13 2020 +0900

    Merge branch 'fix-mrb_open-with-nomem' of https://github.com/dearblue/mruby into dearblue-fix-mrb_open-with-nomem

commit b178914b111dda79a8f36ec4eb3e9d37b76f982e
Author: dearblue <[email protected]>
Date:   Sat Jan 19 22:22:44 2019 +0900

    Fix invalid pointer free inside other heap's block

     1. `e = mrb_obj_alloc(...)`
     2. `e->stack = mrb->c->stack` (`mrb->c->stack` is anywhere in the range `stbase...stend`)
     3. And raised exception by `mrb_malloc()`!
     4. `mrb_free(e->stack)` by GC part (wrong free)

commit 52e3d5d8585daf86af3ed12db5ab0efefbc9b956
Author: dearblue <[email protected]>
Date:   Sat Jan 19 21:55:36 2019 +0900

    Fix memory leak for temporary symbols when out of memory

commit 4c5499b88e47cc6012ad7d7379cb6bc74c6a0b60
Author: dearblue <[email protected]>
Date:   Sun Jan 20 11:42:07 2019 +0900

    Fix uninitialized pointer dereference for debug section

commit 8e993167dec62a9709d6faacd517729ddcedf4f9
Author: dearblue <[email protected]>
Date:   Sun Jan 20 11:41:09 2019 +0900

    Fix memory leak for temporary filenames when out of memory

commit 8b422577e6eae68a28121b88421d937e8707b487
Author: dearblue <[email protected]>
Date:   Sun Jan 20 10:57:51 2019 +0900

    Fix memory leak for irep when out of memory

commit 6b35ebf49a0aa3edb6bbda770ed58681e9c2e6af
Author: dearblue <[email protected]>
Date:   Sun Jan 20 10:55:50 2019 +0900

    Fix uninitialized pointer dereference when do not finished initializing irep

commit 2531f2631e67e0462749618e2344c733a29238f0
Author: dearblue <[email protected]>
Date:   Sun Jan 20 10:48:15 2019 +0900

    Fix NULL pointer dereference when do not finished initializing irep

commit e2d6896ebad13694800af49c2625e106b8440ddf
Author: dearblue <[email protected]>
Date:   Sat Jan 19 12:54:19 2019 +0900

    Fix memory leak for irep when out of memory by `mrb_proc_new()`

commit b6214ff8a0a1c73bc9554e39053878ac50bb683f
Author: dearblue <[email protected]>
Date:   Sat Jan 19 12:53:07 2019 +0900

    Fix memory leak for `khash_t` in `kh_init_size()` when out of memory by `kh_alloc()`

commit 19162dd6c11f0093d0011e7cab83b8f9e84c2c07
Author: dearblue <[email protected]>
Date:   Sun Jan 20 02:15:07 2019 +0900

    Fix memory leak for symbol string when out of memory in `kh_put()`

commit 15e67297ff54bc14ef359d6d1e745d760a4a255a
Author: dearblue <[email protected]>
Date:   Sun Jan 20 02:12:24 2019 +0900

    Fix keep wrong symbol index when out of memory

commit 3f8e2b375244f5441e8d62efa13c6e6a9afecb14
Author: dearblue <[email protected]>
Date:   Sun Jan 20 02:08:13 2019 +0900

    Fix keep wrong symbol capacity when out of memory

commit a3cfe755ab3e758046c3f4e30938ac8d567ed046
Author: dearblue <[email protected]>
Date:   Sat Jan 19 10:11:37 2019 +0900

    Fix NULL pointer dereference `mrb->c` by `mark_context()`

commit d9c7b6be6eb54630b64eea5c35be241e551676e5
Author: dearblue <[email protected]>
Date:   Sun Jan 20 15:25:09 2019 +0900

    Fix protect exception for print error message

commit 100642750e4d549f2e8050f8d6cabdf8825d4495
Author: dearblue <[email protected]>
Date:   Sun Jan 20 11:59:02 2019 +0900

    Protect exception for mruby core initialization

commit 7a0418304ec70764fa215bef3599f5f735222075
Author: dearblue <[email protected]>
Date:   Fri Jan 18 20:38:27 2019 +0900

    Fix memory leak for string object when out of memory

    The `mrb_str_pool()` function has a path to call `malloc()` twice.

    If occurs `NoMemoryError` exception in second `malloc()`,
    first `malloc()` pointer is not freed.

commit fef1c152ce4e52b9e4a34dc23aca5b02907ac639
Author: dearblue <[email protected]>
Date:   Sat Jan 19 13:05:09 2019 +0900

    Fix stack overflow when out of memory

    As a result of this change, no backtrace information is set
    for NoMemoryError (`mrb->nomem_err`).

    Detailes:

    When generating a backtrace, called `mrb_intern_lit()`,
    `mrb_str_new_cstr()` and `mrb_obj_iv_set()` function with
    `exc_debug_info()` function in `src/error.c`.

    If a `NoMemoryError` exception occurs at this time,
    the `exc_debug_info()` function will be called again,
    and in the same way `NoMemoryError` exception raised will result
    in an infinite loop to occurs stack overflow (and SIGSEGV).

commit da7d7f881bbbad9988a3a2b7bad8f2b72ff06bc6
Author: dearblue <[email protected]>
Date:   Sun Jan 20 12:00:38 2019 +0900

    Fix NULL pointer dereference `mrb->nomem_err` when not initialized

    Add internal functions (not `static`):

      * `mrb_raise_nomemory()`
      * `mrb_core_init_abort()`

1 files changed, 8 insertions, 5 deletions

diff --git a/src/debug.c b/src/debug.c
index b44c7d10e..4aeed2ff7 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -204,11 +204,14 @@ mrb_debug_info_free(mrb_state *mrb, mrb_irep_debug_info *d)
 
   if (!d) { return; }
 
-  for (i = 0; i < d->flen; ++i) {
-    mrb_assert(d->files[i]);
-    mrb_free(mrb, d->files[i]->lines.ptr);
-    mrb_free(mrb, d->files[i]);
+  if (d->files) {
+    for (i = 0; i < d->flen; ++i) {
+      if (d->files[i]) {
+        mrb_free(mrb, d->files[i]->lines.ptr);
+        mrb_free(mrb, d->files[i]);
+      }
+    }
+    mrb_free(mrb, d->files);
   }
-  mrb_free(mrb, d->files);
   mrb_free(mrb, d);
 }