[RFA PATCH] Recognize ggc_free'd memory in pretty-printers.

[Richard Biener]

On Fri, Jun 7, 2019 at 11:11 PM Jason Merrill <jason@redhat.com> wrote:
>
> A tree node that has been poisoned by ggc_free is easily recognizable by the
> TREE_CODE 0xa5a5; let's look for that rather than access some random memory off
> the end of the array.
>
> OK for trunk?

OK.

Richard.

>         * gdbhooks.py (TreePrinter.to_string): Recognize ggc_free'd memory.
>         * tree.c (get_tree_code_name): Likewise.
>         * print-tree.c (print_node): Only briefly print a node with an
>         invalid code.
> ---
>  gcc/print-tree.c | 16 +++++++++-------
>  gcc/tree.c       |  6 +++++-
>  gcc/gdbhooks.py  |  3 +++
>  gcc/ChangeLog    |  7 +++++++
>  4 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/gcc/print-tree.c b/gcc/print-tree.c
> index 81b66a1891b..f69a2c26679 100644
> --- a/gcc/print-tree.c
> +++ b/gcc/print-tree.c
> @@ -233,6 +233,15 @@ print_node (FILE *file, const char *prefix, tree node, int indent,
>      return;
>
>    code = TREE_CODE (node);
> +
> +  /* It is unsafe to look at any other fields of a node with ERROR_MARK or
> +     invalid code.  */
> +  if (code == ERROR_MARK || code >= MAX_TREE_CODES)
> +    {
> +      print_node_brief (file, prefix, node, indent);
> +      return;
> +    }
> +
>    tclass = TREE_CODE_CLASS (code);
>
>    /* Don't get too deep in nesting.  If the user wants to see deeper,
> @@ -251,13 +260,6 @@ print_node (FILE *file, const char *prefix, tree node, int indent,
>        return;
>      }
>
> -  /* It is unsafe to look at any other fields of an ERROR_MARK node.  */
> -  if (code == ERROR_MARK)
> -    {
> -      print_node_brief (file, prefix, node, indent);
> -      return;
> -    }
> -
>    /* Allow this function to be called if the table is not there.  */
>    if (table)
>      {
> diff --git a/gcc/tree.c b/gcc/tree.c
> index 43ce44fcee4..4ba0135dfbb 100644
> --- a/gcc/tree.c
> +++ b/gcc/tree.c
> @@ -13444,7 +13444,11 @@ get_tree_code_name (enum tree_code code)
>    const char *invalid = "<invalid tree code>";
>
>    if (code >= MAX_TREE_CODES)
> -    return invalid;
> +    {
> +      if (code == 0xa5a5)
> +       return "ggc_freed";
> +      return invalid;
> +    }
>
>    return tree_code_name[code];
>  }
> diff --git a/gcc/gdbhooks.py b/gcc/gdbhooks.py
> index 39f5c4772f9..e08208e1533 100644
> --- a/gcc/gdbhooks.py
> +++ b/gcc/gdbhooks.py
> @@ -222,6 +222,9 @@ class TreePrinter:
>          # extern const enum tree_code_class tree_code_type[];
>          # #define TREE_CODE_CLASS(CODE)        tree_code_type[(int) (CODE)]
>
> +        if val_TREE_CODE == 0xa5a5:
> +            return '<ggc_freed 0x%x>' % intptr(self.gdbval)
> +
>          val_tree_code_type = gdb.parse_and_eval('tree_code_type')
>          val_tclass = val_tree_code_type[val_TREE_CODE]
>
> diff --git a/gcc/ChangeLog b/gcc/ChangeLog
> index fa7a5adefb2..8a083599c99 100644
> --- a/gcc/ChangeLog
> +++ b/gcc/ChangeLog
> @@ -1,3 +1,10 @@
> +2019-06-07  Jason Merrill  <jason@redhat.com>
> +
> +       * gdbhooks.py (TreePrinter.to_string): Recognize ggc_free'd memory.
> +       * tree.c (get_tree_code_name): Likewise.
> +       * print-tree.c (print_node): Only briefly print a node with an
> +       invalid code.
> +
>  2019-06-07  Jakub Jelinek  <jakub@redhat.com>
>
>         * Makefile.in (genprogerr): Add condmd.
>
> base-commit: 5f93e2e757ba1dfd0514b3661b6d737ea5492fa9
> --
> 2.20.1
>