Bug 26276 - Need a mechanism to determine stack extent
Reviewed by Oliver Hunt.
JavaScriptCore:
This patch adds a class 'StackBounds', to hold information about the machine stack.
The implementation of this class broadly adheres to the current implmentation of
stack limit checking, and as such does not solve the problem of determining stack
extent, but gives us a common place to do so.
Currently two mechanism are provided to determine the stack origin (the point the
stack is growing away from). currentThreadStackBase() in Collector provides a
more accurate determination of the stack origin, so use this to calculate
StackBounds::m_origin; WTFThreadData::approximatedStackStart is less accurate, and
as such can be removed. Cache the StackBounds on WTFThreadData such that they
need only be determined once per thread, and for non-API contexts cache this
information in JSGlobalData, to save a thread-specific access.
For the time being retain the estimate of stack size used by JSC's parser
(128 * sizeof(void*) * 1024), with a view to replacing this with something more
accurate in the near future.
(JSC::JSParser::canRecurse):
(JSC::JSParser::JSParser):
Change to use StackBounds.
(JSC::Heap::registerThread):
(JSC::Heap::markCurrentThreadConservativelyInternal):
Change to use StackBounds, cached on JSGlobalData.
- runtime/JSGlobalData.cpp:
(JSC::JSGlobalData::JSGlobalData):
(JSC::JSGlobalData::stack):
Add a cached copy of StackBounds.
- wtf/StackBounds.cpp: Copied from JavaScriptCore/runtime/Collector.cpp.
(WTF::estimateStackBound):
(WTF::StackBounds::initialize):
(WTF::getStackMax):
Copy code from Collector.cpp to determine stack origin.
- wtf/StackBounds.h: Added.
(WTF::StackBounds::StackBounds):
No argument constructor; returns a null StackBounds.
(WTF::StackBounds::currentThreadStackBounds):
Returns a StackBounds object representing the stack limits
of the current thread.
(WTF::StackBounds::origin):
Returns to stack origin (the point the stack is growing away
from; the highest extent of the stack on machines where the
stack grows downwards.
(WTF::StackBounds::recursionLimit):
Returns a limit value that is 'a comfortable distance from
the end of the stack'. Our concept of this is currently 1 page
away from the end, however the default value may be tuned in
the future, and clients may override passing a larger delta;
should only be called on StackBounds object representing the
stack of the thread this method is called on (checked by
checkConsistency).
(WTF::StackBounds::recursionCheck):
Checks whether we are currently 'a comfortable distance from
the end of the stack'. Our concept of this is currently 1 page
away from the end, however the default value may be tuned in
the future, and clients may override passing a larger delta
to apply when checking, if they wish to do so. This method
should only be called on StackBounds object representing the
stack of the thread this method is called on (checked by
checkConsistency).
(WTF::StackBounds::current):
Approximate current stack position. On machines where the stack
is growing downwards this is the lowest address that might need
conservative collection.
(WTF::StackBounds::isGrowingDownward):
True for all platforms other than WINCE, which has to check.
(WTF::StackBounds::checkConsistency):
This is called in methods that shoulds only be operating on a
valid set of bounds; as such we expect m_origin != m_bounds
(i.e. stack size != zero) - we're really testing that this
object is not null (the constructor initializes both fields
to zero). Also checks that current() is within the stack's
bounds.
(WTF::WTFThreadData::WTFThreadData):
(WTF::WTFThreadData::stack):
Add the StackBounds member variable.
JavaScriptGlue:
Add forwarding header for StackBounds.h.
- ForwardingHeaders/wtf/StackBounds.h: Added.
WebCore:
Add forwarding header for StackBounds.h.
- ForwardingHeaders/wtf/StackBounds.h: Added.
