:In general, a given number of guard pages is insufficient for some (perhaps
:non-existent) applications. The basic idea is to catch typical stack
:overflow. Trying to always catch stack overflow is not practical. Since
:this is a heuristic error detection technique, I'm not sure how much
:work/complexity it's worth to paramaterize the number of guard pages for
:each mapping.
:
:Jason
I think it's important. Pthreads has calls to allow
the user to set the stack size. At the moment our uthreads library
malloc()'s the stack in this case. Eventually we want to be able
to rewrite the code to use mmap() for all the stack types and then
keep track of how big they were in the freelist for reuse.
I think the following patch to our threads library, when combined
with the guard-3.diff, optimizes our threads library for default
thread stacks. I did a very simple test and it appears to work.
One vm_map_entry is created every 8 64K pthread stacks with
vm.map_entry_blk_opt set to 524288.
The native port of the linux threads library can probably be patched
fairly easily.
The real linux threads library (/usr/compat/linux/lib/libpthread)
mmap()s guard pages separately, which is impossible to optimize. We
would need a special freebsd version of the library to get the
VM map optimizations.
It may be possible to eventually get rid of vm.map_entry_blk_opt
entirely but that requires more work then I have time for right now
(we basically have to support negative vm_object offsets in order
to be able to grow an anonymous memory object downward to do it right).
-Matt
Matthew Dillon
<[EMAIL PROTECTED]>
Index: uthread/uthread_create.c
===================================================================
RCS file: /home/ncvs/src/lib/libc_r/uthread/uthread_create.c,v
retrieving revision 1.24
diff -u -r1.24 uthread_create.c
--- uthread/uthread_create.c 2000/01/19 07:04:46 1.24
+++ uthread/uthread_create.c 2000/02/19 03:04:01
@@ -137,12 +137,23 @@
PANIC("Cannot unlock gc mutex");
/* Stack: */
+#if defined(__FreeBSD__)
+ if (mmap((char *)stack - PTHREAD_STACK_GUARD,
+ PTHREAD_STACK_DEFAULT + PTHREAD_STACK_GUARD,
+ PROT_READ | PROT_WRITE,
+ MAP_STACK | MAP_GUARDED,
+ -1, PTHREAD_STACK_GUARD) == MAP_FAILED) {
+ ret = EAGAIN;
+ free(new_thread);
+ }
+#else
if (mmap(stack, PTHREAD_STACK_DEFAULT,
PROT_READ | PROT_WRITE, MAP_STACK,
-1, 0) == MAP_FAILED) {
ret = EAGAIN;
free(new_thread);
}
+#endif
}
}
/*
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