[PATCH] Remove dwarf2_per_objfile_free and use after free of dwarf2_per_objfile

[Simon Marchi]

On 2018-01-13 13:10, Simon Marchi wrote:
> I got some crashes while doing some work with dwarf2_per_objfile.  It
> turns out that dwarf2_per_objfile_free is using the dwarf2_per_objfile
> objects after their destructor has ran.
> 
> The easiest way to reproduce this is to run the inferior twice (do
> "start" twice).  Currently, it goes unnoticed, but when I tried to
> change all_comp_units and all_type_units to std::vectors, things 
> started
> crashing.
> 
> The dwarf2_per_objfile objects get destroyed here:
> 
>  #0  dwarf2_per_objfile::~dwarf2_per_objfile (this=0x35afe70,
> __in_chrg=<optimized out>) at
> /home/emaisin/src/binutils-gdb/gdb/dwarf2read.c:2422
>  #1  0x0000000000833282 in dwarf2_free_objfile (objfile=0x356cff0) at
> /home/emaisin/src/binutils-gdb/gdb/dwarf2read.c:25363
>  #2  0x0000000000699255 in elf_symfile_finish (objfile=0x356cff0) at
> /home/emaisin/src/binutils-gdb/gdb/elfread.c:1309
>  #3  0x0000000000911ed3 in objfile::~objfile (this=0x356cff0,
> __in_chrg=<optimized out>) at
> /home/emaisin/src/binutils-gdb/gdb/objfiles.c:674
> 
> and just after that the dwarf2read per-objfile registry cleanup 
> function
> gets called:
> 
>  #0  dwarf2_per_objfile_free (objfile=0x356cff0, d=0x35afe70) at
> /home/emaisin/src/binutils-gdb/gdb/dwarf2read.c:25667
>  ... registry boilerplate ...
>  #4  0x00000000009103ea in objfile_free_data (container=0x356cff0) at
> /home/emaisin/src/binutils-gdb/gdb/objfiles.c:61
>  #5  0x0000000000911ee2 in objfile::~objfile (this=0x356cff0,
> __in_chrg=<optimized out>) at
> /home/emaisin/src/binutils-gdb/gdb/objfiles.c:678
> 
> In dwarf2_per_objfile_free, we access fields of the dwarf2_per_objfile
> object, which is invalid since its destructor has been executed.
> 
> This patch moves the content of dwarf2_per_objfile_free to the
> destructor of dwarf2_per_objfile.  The call to
> register_objfile_data_with_cleanup in _initialize_dwarf2_read can be
> changed to the simpler register_objfile_data.
> 
> gdb/ChangeLog:
> 
> 	* dwarf2read.c (free_dwo_files): Add forward-declaration.
> 	(dwarf2_per_objfile::~dwarf2_per_objfile): Move content from
> 	dwarf2_per_objfile_free here.
> 	(dwarf2_per_objfile_free): Remove.
> 	(_initialize_dwarf2_read): Don't register
> 	dwarf2_per_objfile_free as a registry cleanup.
> ---
>  gdb/dwarf2read.c | 57 
> ++++++++++++++++++++++++--------------------------------
>  1 file changed, 24 insertions(+), 33 deletions(-)
> 
> diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
> index dca2fe9..8a43b8d 100644
> --- a/gdb/dwarf2read.c
> +++ b/gdb/dwarf2read.c
> @@ -2416,6 +2416,8 @@ dwarf2_per_objfile::dwarf2_per_objfile (struct
> objfile *objfile_,
>      locate_sections (obfd, sec, *names);
>  }
> 
> +static void free_dwo_files (htab_t dwo_files, struct objfile 
> *objfile);
> +
>  dwarf2_per_objfile::~dwarf2_per_objfile ()
>  {
>    /* Cached DIE trees use xmalloc and the comp_unit_obstack.  */
> @@ -2427,6 +2429,27 @@ dwarf2_per_objfile::~dwarf2_per_objfile ()
>    if (line_header_hash)
>      htab_delete (line_header_hash);
> 
> +  for (int ix = 0; ix < n_comp_units; ++ix)
> +   VEC_free (dwarf2_per_cu_ptr, all_comp_units[ix]->imported_symtabs);
> +
> +  for (int ix = 0; ix < n_type_units; ++ix)
> +    VEC_free (dwarf2_per_cu_ptr,
> +	      all_type_units[ix]->per_cu.imported_symtabs);
> +  xfree (all_type_units);
> +
> +  VEC_free (dwarf2_section_info_def, types);
> +
> +  if (dwo_files)
> +    free_dwo_files (dwo_files, objfile);
> +  if (dwp_file)
> +    gdb_bfd_unref (dwp_file->dbfd);
> +
> +  if (dwz_file && dwz_file->dwz_bfd)
> +    gdb_bfd_unref (dwz_file->dwz_bfd);
> +
> +  if (index_table != NULL)
> +    index_table->~mapped_index ();
> +
>    /* Everything else should be on the objfile obstack.  */
>  }
> 
> @@ -25659,37 +25682,6 @@ show_dwarf_cmd (const char *args, int 
> from_tty)
>    cmd_show_list (show_dwarf_cmdlist, from_tty, "");
>  }
> 
> -/* Free data associated with OBJFILE, if necessary.  */
> -
> -static void
> -dwarf2_per_objfile_free (struct objfile *objfile, void *d)
> -{
> -  struct dwarf2_per_objfile *data = (struct dwarf2_per_objfile *) d;
> -  int ix;
> -
> -  for (ix = 0; ix < data->n_comp_units; ++ix)
> -   VEC_free (dwarf2_per_cu_ptr, 
> data->all_comp_units[ix]->imported_symtabs);
> -
> -  for (ix = 0; ix < data->n_type_units; ++ix)
> -    VEC_free (dwarf2_per_cu_ptr,
> -	      data->all_type_units[ix]->per_cu.imported_symtabs);
> -  xfree (data->all_type_units);
> -
> -  VEC_free (dwarf2_section_info_def, data->types);
> -
> -  if (data->dwo_files)
> -    free_dwo_files (data->dwo_files, objfile);
> -  if (data->dwp_file)
> -    gdb_bfd_unref (data->dwp_file->dbfd);
> -
> -  if (data->dwz_file && data->dwz_file->dwz_bfd)
> -    gdb_bfd_unref (data->dwz_file->dwz_bfd);
> -
> -  if (data->index_table != NULL)
> -    data->index_table->~mapped_index ();
> -}
> -
> -
>  /* The "save gdb-index" command.  */
> 
>  /* Write SIZE bytes from the buffer pointed to by DATA to FILE, with
> @@ -27321,8 +27313,7 @@ _initialize_dwarf2_read (void)
>  {
>    struct cmd_list_element *c;
> 
> -  dwarf2_objfile_data_key
> -    = register_objfile_data_with_cleanup (NULL, 
> dwarf2_per_objfile_free);
> +  dwarf2_objfile_data_key = register_objfile_data ();
> 
>    add_prefix_cmd ("dwarf", class_maintenance, set_dwarf_cmd, _("\
>  Set DWARF specific variables.\n\

I pushed this patch.

Simon