From: Paul Eggert <eggert@cs.ucla.edu>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 18410@debbugs.gnu.org
Subject: bug#18410: Use SAFE_ALLOCA etc. to avoid unbounded stack allocation.
Date: Sun, 07 Sep 2014 13:33:10 -0700 [thread overview]
Message-ID: <540CC106.8040705@cs.ucla.edu> (raw)
In-Reply-To: <83bnqrcq7u.fsf@gnu.org>
Eli Zaretskii wrote:
> MAX_ALLOCA is a relatively small number compared to the stack space
> available on modern systems, so I see no reason to fail and exit in
> these cases, it sounds too drastic.
Usually MAX_ALLOCA-related code falls back on malloc, and does not exit
merely because a request was larger. callproc.c's child_setup function
is special, though, as it executes in a vforked child that cannot safely
call malloc because that would screw up the parent's malloc arena. In
this special case the child exits (Emacs itself doesn't), so it's not
that drastic. It'd be nicer if Emacs would allocate the memory before
vforking the child, as that would avoid the limitation, but I daresay
it's not urgent to fix this. It should be commented better, though, and
I gave that a shot in trunk bzr 117837.
Quite possibly we should increase MAX_ALLOCA on many modern systems. As
I recall we last discussed that in July, and Stefan was worried about
max-lisp-eval-depth * MAX_ALLOCA * N overflowing the C stack, where N is
the maximum nesting depth of SAFE_ALLOCA-using C functions between Lisp
functions. Perhaps some of that discussion is moot now, with the stack
overflow checking that Dmitry added last month?
next prev parent reply other threads:[~2014-09-07 20:33 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-05 6:08 bug#18410: Use SAFE_ALLOCA etc. to avoid unbounded stack allocation Paul Eggert
2014-09-05 8:45 ` Dmitry Antipov
2014-09-05 15:01 ` Paul Eggert
2014-09-05 15:44 ` Stefan Monnier
2014-09-05 16:04 ` Andreas Schwab
2014-09-05 17:22 ` Stefan Monnier
2014-09-05 8:59 ` Dmitry Antipov
2014-09-05 15:03 ` Paul Eggert
2014-09-07 7:20 ` Paul Eggert
2014-09-07 17:09 ` Eli Zaretskii
2014-09-07 20:33 ` Paul Eggert [this message]
2014-09-08 2:22 ` Stefan Monnier
2014-09-08 2:35 ` Eli Zaretskii
2014-09-08 2:43 ` Stefan Monnier
2014-09-08 2:38 ` Paul Eggert
2014-09-08 3:17 ` Demetrios Obenour
2014-09-08 3:19 ` Daniel Colascione
2014-09-08 3:20 ` Demetrios Obenour
2014-09-08 7:26 ` Dmitry Antipov
2014-09-08 2:36 ` Eli Zaretskii
2014-09-08 12:48 ` Stefan Monnier
2014-09-09 13:17 ` Eli Zaretskii
2014-09-09 13:49 ` Stefan Monnier
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