Tcl Source Code

TclpCheckStackSpace() (in unix/tclUnixInit.c) should be
implemented for unix - it is already implemented for
both Mac and Win.

It's role is to prevent C-stack overflow, producing an
error instead of who knows what.

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IIUC, 746378 started on this approach and improved it a lot
- in particular, making it work also for threaded builds. 
If that is correct, this patch is superceded by 746378.

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dup of 746378 - we should compare the differences between 
these two approaches.

File Added - 18530: stackSpace3.patch.gz

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New "production-ready" stackSpace3.patch, for review.

It is still missing the adaptation to threaded builds; as
before, it does not guard against stack-heap collisions.

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Note that this patch implements a "light"
TclpCheckStackSpace: it monitors the remaining stack space
with respect to the maximum allowed by the OS, but *not*
against stack-heap collisions. The win implementation (and
presumably the mac too) monitor both.

Joe English has proposed a solution for linux/gcc in
non-threaded builds that monitors the stack-heap distance
"as long as you haven't called mmap()/shmget/whatever (not
sure how that affects the memory map)". It is done by
setting the condition to monitor to

((&here > tclMinCStackPos) && (&here  > sbrk(0) +
tclMinCStackSize))

File Added - 18465: stackSpace2.patch.gz

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OKnow ...

File Deleted - 18464: 

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Aargh! Removing patch2 2 (typos); back in a few minutes!

File Added - 18464: stackSpace2.patch.gz

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Improved stackSpace2.patch:
  * corrections as suggested by Donal
  * more checks and default behaviour in tclUnixInit.c

File Added - 18461: configure.patch

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Looks mostly good to me, both with GCC and with SunPro CC on
Solaris/SPARC, except for the configure script which ought
to print out more of what it is doing with your stackspace
check as well as cacheing the values concerned.  Luckily,
this is easy to add - see the extra patch which I supply
which should be applied *after* yours.

The other minor quibble I've noticed (from using SunPro CC)
is that you shouldn't do
   #undef TclpCheckStackSpace()
but rather just
   #undef TclpCheckStackSpace

(SunPro CC is great, because it moans about completely
different things to GCC. :^)

File Added - 18399: stackSpace.patch.gz

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I attach a patch (gzipped) that implements
TclpCheckStackSpace.

Please test it on different unixen - it runs ok with gcc
(egcs-2.91.66, glibc 2.1.3) on linux/intel.

Some comments:

1. in order to use, the new function TclpInitCheckStackSpace
(tclUnixInit.c) should be called with a stack address as
early as possible. In the patch, this is done from Tcl_Main
so that the writers of special shells do not have to worry
about it.

2. as it is here, the functionality is not available for
embedders - the new function is not declared in the stubs
tables. If the functionality is deemed necessary, it may be
worth considering making it public (or called from some new
Tcl_InitializeSystem). That would require TIPping.

3. if TclpInitCheckStackSpace is never called, the behaviour
is the same as without the patch: it is always assumed that
there is enough stack space to continue.

Comments welcome!