On Tue, Jul 13, 2021 at 5:10 AM Alexandre Oliva <ol...@adacore.com> wrote:
>
>
> If an artificial label created for a landing pad ends up being
> dropped in favor of a user-supplied label, the user-supplied label
> inherits the landing pad index, but the post_landing_pad field is not
> adjusted to point to the new label.
>
> This patch fixes the problem, and adds verification that we don't
> remove a label that's still used as a landing pad.
>
> The circumstance in which this problem can be hit was unusual: removal
> of a block with an unreachable label moves the label to some other
> unrelated block, in case its address is taken. In the case at hand
> (pr42739.C, complicated by wrappers and cleanups), the chosen block
> happened to be an EH landing pad. (A followup patch will change that.)
>
> Regstrapped on x86_64-linux-gnu. Ok to install?
OK.
>
> for gcc/ChangeLog
>
> * tree-cfg.c (cleanup_dead_labels_eh): Update
> post_landing_pad label upon change of landing pad block's
> primary label.
> (cleanup_dead_labels): Check that a removed label is not that
> of a landing pad.
> ---
> gcc/tree-cfg.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> index c73e1cbdda6b9..1f0f4a2c6eb2c 100644
> --- a/gcc/tree-cfg.c
> +++ b/gcc/tree-cfg.c
> @@ -1481,6 +1481,7 @@ cleanup_dead_labels_eh (label_record *label_for_bb)
> if (lab != lp->post_landing_pad)
> {
> EH_LANDING_PAD_NR (lp->post_landing_pad) = 0;
> + lp->post_landing_pad = lab;
> EH_LANDING_PAD_NR (lab) = lp->index;
> }
> }
> @@ -1707,7 +1708,10 @@ cleanup_dead_labels (void)
> || FORCED_LABEL (label))
> gsi_next (&i);
> else
> - gsi_remove (&i, true);
> + {
> + gcc_checking_assert (EH_LANDING_PAD_NR (label) == 0);
> + gsi_remove (&i, true);
> + }
> }
> }
>
>
> --
> Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
> Free Software Activist GNU Toolchain Engineer
> Disinformation flourishes because many people care deeply about injustice
> but very few check the facts. Ask me about <https://stallmansupport.org>
