Re: [PATCH] gdb: Reinitialize objfile::section_offsets during objfile reload

[Tom Tromey <tom@tromey.com>]

Andrew> When building and testing with '-D_GLIBCXX_DEBUG=1' I noticed that the
Andrew> test gdb.base/reload.exp was failing.  This turns out to be because
Andrew> the objfile::section_offsets vector is not reinitialilzed during the
Andrew> objfile reload process, and in this particular test, GDB ends up
Andrew> indexing outside the bounds of the vector.

Tom> Thanks for catching this.

I wonder if this is a regression due to 

commit 6a053cb1ff643cec3349d7f2f47ae5573f82d613
Author: Tom Tromey <tromey@adacore.com>
Date:   Mon Jan 6 14:34:52 2020 -0700

    Change section_offsets to a std::vector

See appended.

I think at the time I thought removing this code would simply preserve
the offsets.  But maybe we instead should std::move the offsets out of
the objfile and then move them back in?

This change would preserve the old status quo.

Tom

@@ -2479,9 +2468,6 @@ reread_symbols (void)
       new_modtime = new_statbuf.st_mtime;
       if (new_modtime != objfile->mtime)
 	{
-	  struct section_offsets *offsets;
-	  int num_offsets;
-
 	  printf_filtered (_("`%s' has changed; re-reading symbols.\n"),
 			   objfile_name (objfile));
 
@@ -2556,14 +2542,6 @@ reread_symbols (void)
 	    error (_("Can't read symbols from %s: %s."), objfile_name (objfile),
 		   bfd_errmsg (bfd_get_error ()));
 
-	  /* Save the offsets, we will nuke them with the rest of the
-	     objfile_obstack.  */
-	  num_offsets = objfile->num_sections;
-	  offsets = ((struct section_offsets *)
-		     alloca (SIZEOF_N_SECTION_OFFSETS (num_offsets)));
-	  memcpy (offsets, objfile->section_offsets,
-		  SIZEOF_N_SECTION_OFFSETS (num_offsets));
-
 	  objfile->reset_psymtabs ();
 
 	  /* NB: after this call to obstack_free, objfiles_changed
@@ -2595,15 +2573,6 @@ reread_symbols (void)
 
 	  build_objfile_section_table (objfile);
 
-	  /* We use the same section offsets as from last time.  I'm not
-	     sure whether that is always correct for shared libraries.  */
-	  objfile->section_offsets = (struct section_offsets *)
-	    obstack_alloc (&objfile->objfile_obstack,
-			   SIZEOF_N_SECTION_OFFSETS (num_offsets));
-	  memcpy (objfile->section_offsets, offsets,
-		  SIZEOF_N_SECTION_OFFSETS (num_offsets));
-	  objfile->num_sections = num_offsets;
-
 	  /* What the hell is sym_new_init for, anyway?  The concept of
 	     distinguishing between the main file and additional files
 	     in this way seems rather dubious.  */