[binutils-gdb] gdb: fix "passing NULL to memcpy" UBsan error in dwarf2/cooked-index.c

[Simon Marchi <simark@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=a8b7a1391135b63de73c1bf0e0a2f8f5dc8c6ba6

commit a8b7a1391135b63de73c1bf0e0a2f8f5dc8c6ba6
Author: Simon Marchi <simon.marchi@efficios.com>
Date:   Tue Apr 12 14:37:24 2022 -0400

    gdb: fix "passing NULL to memcpy" UBsan error in dwarf2/cooked-index.c
    
    Reading a simple file compiled with :
    
        $ gcc -DONE=1 -gdwarf-4 -g3  test.c
        $ gcc --version
        gcc (Ubuntu 9.4.0-1ubuntu1~20.04) 9.4.0
    
    I get:
    
        Reading symbols from /tmp/cwd/a.out...
        /home/smarchi/src/binutils-gdb/gdb/dwarf2/cooked-index.c:332:11: runtime error: null pointer passed as argument 2, which is declared to never be null
    
    It looks like even if the size is 0 (the size of the `entries` vector is
    0), we shouldn't be passing a NULL pointer to memcpy.  And
    `entries.data ()` returns NULL.
    
    Fix that by using std::vector::insert to insert the items of entries
    into m_entries.  I haven't checked, but it should essentially compile
    down to a memcpy, since the vector elements are trivially copyiable.
    
    Change-Id: I75f1c901e9b522e42e89eb5936e2c70d68eb21e5

Diff:
---
 gdb/dwarf2/cooked-index.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/gdb/dwarf2/cooked-index.c b/gdb/dwarf2/cooked-index.c
index 784c06ea04b..b66ef5a1c64 100644
--- a/gdb/dwarf2/cooked-index.c
+++ b/gdb/dwarf2/cooked-index.c
@@ -327,10 +327,8 @@ cooked_index_vector::finalize ()
 	m_entries = std::move (entries);
       else
 	{
-	  size_t old_size = m_entries.size ();
-	  m_entries.resize (m_entries.size () + entries.size ());
-	  memcpy (m_entries.data () + old_size,
-		  entries.data (), entries.size () * sizeof (entries[0]));
+	  m_entries.reserve (m_entries.size () + entries.size ());
+	  m_entries.insert (m_entries.end (), entries.begin (), entries.end ());
 	}
     }