Re: Regression with -D_GLIBCXX_DEBUG [Re: [PATCH 1/5] Make delim_string_to_char_ptr_vec return an std::vector]

Simon Marchi
2018-04-10T20:52:40Z

On 2018-04-10 04:39 PM, Jan Kratochvil wrote:
> On Tue, 10 Apr 2018 22:32:46 +0200, Simon Marchi wrote:
>> Of course, thanks for reporting. Does this fix it?
>>
>> >From fddee555819b2631920bf4a86854bb0d76ac121f Mon Sep 17 00:00:00 2001
>> From: Simon Marchi <simon.marchi@ericsson.com>
>> Date: Tue, 10 Apr 2018 16:31:52 -0400
>> Subject: [PATCH] Iterate by index
>
> Yes.

Thanks, here's what I pushed:

From 6e22e10d63addd60f39114cef81ade290b15b2c8 Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@ericsson.com>
Date: Tue, 10 Apr 2018 16:50:59 -0400
Subject: [PATCH] Iterate by index in auto_load_safe_path_vec_update

As reported by Jan, we get this error when building with -D_GLIBCXX_DEBUG:

/usr/include/c++/7/debug/safe_iterator.h:297:
Error: attempt to increment a singular iterator.
Objects involved in the operation:
iterator "this" @ 0x0x7fffffffd140 {
type = __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<std::unique_ptr<char, gdb::xfree_deleter<char> >*, std::__cxx1998::vector<std::unique_ptr<char, gdb::xfree_deleter<char> >, std::allocator<std::unique_ptr<char, gdb::xfree_deleter<char> > > > >, std::__debug::vector<std::unique_ptr<char, gdb::xfree_deleter<char> >, std::allocator<std::unique_ptr<char, gdb::xfree_deleter<char> > > > > (mutable iterator);
state = singular;
references sequence with type 'std::__debug::vector<std::unique_ptr<char, gdb::xfree_deleter<char> >, std::allocator<std::unique_ptr<char, gdb::xfree_deleter<char> > > >' @ 0x0x265db40
}

The bug was introduced by commit

commit e80aaf6183c6692ecc167bf26cbdc53f8f1a55f0
Author: Simon Marchi <simon.marchi@polymtl.ca>
Date: Fri Mar 2 23:22:06 2018 -0500
Make delim_string_to_char_ptr_vec return an std::vector

The problem is that we iterate using a range-based for on a vector to
which we push in the loop. Pushing to the vector invalidates the
iterator used in the loop. Instead, change the code to iterate by index
as was done in the previous code.

gdb/ChangeLog:

* auto-load.c (auto_load_safe_path_vec_update): Iterate by
index.
---
gdb/ChangeLog | 5 +++++
gdb/auto-load.c | 7 +++----
2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d46ecdd..6ed9d6c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-04-10 Simon Marchi <simon.marchi@ericsson.com>
+
+ * auto-load.c (auto_load_safe_path_vec_update): Iterate by
+ index.
+
2018-04-10 Pedro Alves <palves@redhat.com>

* gdbthread.h (finish_thread_state_cleanup): Delete declaration.
diff --git a/gdb/auto-load.c b/gdb/auto-load.c
index e426468..33d282a 100644
--- a/gdb/auto-load.c
+++ b/gdb/auto-load.c
@@ -197,20 +197,19 @@ auto_load_expand_dir_vars (const char *string)
static void
auto_load_safe_path_vec_update (void)
{
- unsigned len;
- int ix;
-
if (debug_auto_load)
fprintf_unfiltered (gdb_stdlog,
_("auto-load: Updating directories of \"%s\".\n"),
auto_load_safe_path);

auto_load_safe_path_vec = auto_load_expand_dir_vars (auto_load_safe_path);
+ size_t len = auto_load_safe_path_vec.size ();

/* Apply tilde_expand and gdb_realpath to each AUTO_LOAD_SAFE_PATH_VEC
element. */
- for (gdb::unique_xmalloc_ptr<char> &in_vec : auto_load_safe_path_vec)
+ for (size_t i = 0; i < len; i++)
{
+ gdb::unique_xmalloc_ptr<char> &in_vec = auto_load_safe_path_vec[i];
gdb::unique_xmalloc_ptr<char> expanded (tilde_expand (in_vec.get ()));
gdb::unique_xmalloc_ptr<char> real_path = gdb_realpath (expanded.get ());

--
2.7.4