Re: adjust landing pads when changing main label
On Tue, Jul 13, 2021 at 5:10 AM Alexandre Oliva 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 ();
> else
> - gsi_remove (, true);
> + {
> + gcc_checking_assert (EH_LANDING_PAD_NR (label) == 0);
> + gsi_remove (, true);
> + }
> }
> }
>
>
> --
> Alexandre Oliva, happy hackerhttps://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
adjust landing pads when changing main label
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?
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 ();
else
- gsi_remove (, true);
+ {
+ gcc_checking_assert (EH_LANDING_PAD_NR (label) == 0);
+ gsi_remove (, true);
+ }
}
}
--
Alexandre Oliva, happy hackerhttps://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
