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Simplify fork code setting up child stack info 

* fork.cc (frok::parent): Simplify code propagating stack setup to
        child process.  Tweak comments.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2015-07-07 17:05:20 +02:00
parent c9b3716279
commit 606013bcf1
2 changed files with 26 additions and 30 deletions
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5
winsup/cygwin/ChangeLog
View File

@ -1,3 +1,8 @@
2015-07-07 Corinna Vinschen <corinna@vinschen.de>
* fork.cc (frok::parent): Simplify code propagating stack setup to
child process. Tweak comments.
2015-07-06 Yaakov Selkowitz <yselkowi@redhat.com>
* path.cc: Rework basename redefinition handling. Explain why.

51
winsup/cygwin/fork.cc
View File

@ -307,39 +307,30 @@ frok::parent (volatile char * volatile stack_here)
ch.forker_finished = forker_finished;
PTEB teb = NtCurrentTeb ();
ch.stackaddr = teb->DeallocationStack;
ch.stackbottom = _tlsbase;
/* If DeallocationStack is NULL, we're running on an application-provided
stack. If so, the entire stack is committed anyway and StackLimit points
to the allocation address of the stack. Otherwise we're running on a
system-allocated stack and using StackLimit is dangerous, in case the
application encountered a stack overflow and recovered from it via
a signal handler running on an alternate stack. Since stack_here is
the address of the stack pointer we start the child with anyway, we
can set ch.stacktop to this value rounded down to page size. The
child will not need the rest of the stack anyway. */
ch.stackaddr = NtCurrentTeb ()->DeallocationStack;
if (!ch.stackaddr)
ch.stacktop = _tlstop;
else
ch.stacktop = (void *) ((uintptr_t) stack_here & ~wincap.page_size ());
ch.guardsize = 0;
if (&_my_tls != _main_tls)
{
/* We have not been started from the main thread. Fetch the
information required to set up the thread stack identically
in the child. */
if (!ch.stackaddr)
{
/* Pthread with application-provided stack. Don't set up a
PAGE_GUARD page. guardsize == -1 is used in alloc_stack_hard_way
to recognize this type of stack. */
ch.stackaddr = _my_tls.tid->attr.stackaddr;
ch.guardsize = (size_t) -1;
}
else if (_my_tls.tid)
/* If it's a pthread, fetch guardsize from thread attributes. */
ch.guardsize = _my_tls.tid->attr.guardsize;
/* If DeallocationStack is NULL, we're running on an application-provided
stack. If so, the entire stack is committed anyway and StackLimit
points to the allocation address of the stack. Mark in guardsize that
we must not set up guard pages. */
ch.stackaddr = ch.stacktop = _tlstop;
ch.guardsize = (size_t) -1;
}
else
{
/* Otherwise we're running on a system-allocated stack. Since stack_here
is the address of the stack pointer we start the child with anyway, we
can set ch.stacktop to this value rounded down to page size. The
child will not need the rest of the stack anyway. Guardsize depends
on whether we're running on a pthread or not. If pthread, we fetch
the guardpage size from the pthread attribs, otherwise we use the
system default. */
ch.stacktop = (void *) ((uintptr_t) stack_here & ~wincap.page_size ());
ch.guardsize = (&_my_tls != _main_tls && _my_tls.tid)
? _my_tls.tid->attr.guardsize
: wincap.def_guard_page_size ();
}
debug_printf ("stack - bottom %p, top %p, addr %p, guardsize %ly",
ch.stackbottom, ch.stacktop, ch.stackaddr, ch.guardsize);