From: Matt Armstrong <matt@rfc20.org>
To: Pip Cet <pipcet@gmail.com>
Cc: 46988@debbugs.gnu.org
Subject: bug#46988: 28.0.50; Documenting and verifying assumptions about C code not calling quit or GCing
Date: Thu, 11 Mar 2021 15:17:10 -0800 [thread overview]
Message-ID: <874khh7021.fsf@rfc20.org> (raw)
In-Reply-To: <CAOqdjBeA9D4dTsc+crLPoz7b6EBEZ9dWbi5Thq0Zy861fkvRBg@mail.gmail.com>
Pip Cet <pipcet@gmail.com> writes:
> On Wed, Mar 10, 2021 at 6:28 PM Matt Armstrong <matt@rfc20.org> wrote:
>> Why a linked list/stack implementation? How about a global count var
>> that is incremented, decremented, and asserted zero?
>
> Emacs' specpdl implementation is independent of, and probably
> predates, the widespread availability of C exceptions. In fact, as it
> is written today, C exceptions will not work in Emacs C code (neither
> will C++ exceptions), because Emacs uses setjmp / longjmp instead, and
> unwinds the stack by itself. Since I was too lazy to fix it to use
> compatible unwinding routines on supported platforms, I simply created
> a linked list on the stack, unwinding it in unwind_to_catch.
>
>> You wrote that this impl depends on the stack direction, but I can't
>> figure out why. If it is indeed the case, add a comment explaining
>> this?
>
> The unwind_to_catch code checks how far up the stack it has to go by
> comparing the stack pointer to the address of a local variable. You're
> absolutely right about the comment.
Ah, makes perfect sense. Thanks for this and your other responses.
next prev parent reply other threads:[~2021-03-11 23:17 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-07 13:47 bug#46988: 28.0.50; Documenting and verifying assumptions about C code not calling quit or GCing Pip Cet
2021-03-07 14:06 ` Pip Cet
2021-03-08 19:42 ` Lars Ingebrigtsen
2021-03-08 19:57 ` Pip Cet
2021-03-09 14:05 ` Lars Ingebrigtsen
2021-03-10 18:28 ` Matt Armstrong
2021-03-10 19:09 ` Pip Cet
2021-03-11 23:17 ` Matt Armstrong [this message]
2022-06-20 1:41 ` Lars Ingebrigtsen
2022-06-20 11:47 ` Eli Zaretskii
2022-06-23 15:56 ` Pip Cet
2022-06-23 16:08 ` Eli Zaretskii
2022-06-23 16:20 ` Mattias Engdegård
2022-06-23 16:35 ` Eli Zaretskii
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