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Message-ID: <20250102124222.GA3109289@schwarzgerat.orthanc>
Date: Thu, 2 Jan 2025 07:42:22 -0500
From: nick black <dankamongmen@...il.com>
To: musl@...ts.openwall.com
Subject: [patch] don't use SA_ONSTACK for SIGCANCEL
this is not necessarily a bug in musl, but it's certainly close
imho. thanks for the great work on musl over the years!
my alternate stack is not a verdant field to be stomped upon by
wayward signals of the musl golden horde. i expect it to be
used for the signals i have registered with SA_ONSTACK.
there is an argument to be made that "The range of addresses
starting at ss_sp up to but not including ss_sp+ ss_size is
available to the implementation for use as the stack." makes the
alternate signal stack free game. i would be stunned, however,
if some named signal was handled on the alternate stack without
me having called SA_ONSTACK in conjunction with it (and this
would not happen with musl -- only SIGCANCEL acts thus).
this caused problems as noticed in
https://github.com/dankamongmen/notcurses/issues/2828
now, free()ing a stack i still have registered for my thread is
unorthodox, perhaps even questionable. definitely questionable.
if there's no benefit from the SA_ONSTACK here, though, i feel
it serves the Law of Least Astonishment to kill it.
commit 8c4a1758bfd432b677db0bae8e4a1a3482dec31d
Author: nick black <dankamongmen@...il.com>
Date: Thu Jan 2 07:32:10 2025 -0500
[pthread_cancel] don't handle SIGCANCEL on altstack
Don't use the receiving thread's alternate signal
stack for SIGCANCEL; they gave us no permission
to do so.
Signed-off-by: nick black <dankamongmen@...il.com>
diff --git src/thread/pthread_cancel.c src/thread/pthread_cancel.c
index 139a6fc8..8ea0b545 100644
--- src/thread/pthread_cancel.c
+++ src/thread/pthread_cancel.c
@@ -82,7 +82,7 @@ void __testcancel()
static void init_cancellation()
{
struct sigaction sa = {
- .sa_flags = SA_SIGINFO | SA_RESTART | SA_ONSTACK,
+ .sa_flags = SA_SIGINFO | SA_RESTART,
.sa_sigaction = cancel_handler
};
memset(&sa.sa_mask, -1, _NSIG/8);
--
nick black -=- https://nick-black.com
to make an apple pie from scratch,
you need first invent a universe.
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