Handle implicit stack overflow without affecting stack walks
This changes the way in which implicit stack overflows are handled
to satisfy concerns about changes to the stack walk code.
Instead of creating a gap in the stack and checking for it in
the stack walker, use the ManagedStack infrastructure to concoct
an invisible gap that will never be seen by a stack walk.
Also, this uses madvise to tell the kernel that the main stack's
protected region will probably never be accessed, and instead
of using memset to map the pages in, use memcpy to read from
them. This will save 32K on the main stack.
Also adds a 'signals' verbosity level as per a review request.
Bug: 14066862
Change-Id: I5257305feeaea241d11e6aa6f021d2a81da20b81
diff --git a/runtime/arch/arm/quick_entrypoints_arm.S b/runtime/arch/arm/quick_entrypoints_arm.S
index bc80644..dcf4561 100644
--- a/runtime/arch/arm/quick_entrypoints_arm.S
+++ b/runtime/arch/arm/quick_entrypoints_arm.S
@@ -235,6 +235,31 @@
*/
ONE_ARG_RUNTIME_EXCEPTION art_quick_throw_no_such_method, artThrowNoSuchMethodFromCode
+ /*
+ * Invoke stack overflow exception from signal handler.
+ * On entry:
+ * r9: thread
+ * sp: address of last known frame
+ * r12: address of next valid SP below protected region in stack
+ *
+ * This is deceptively simple but hides some complexity. It is called in the case of
+ * a stack overflow condition during implicit checks. The signal handler has been
+ * called by the kernel due to a load from the protected stack region. The handler
+ * works out the address of the previous frame and passes this in SP. However there
+ * is a piece of memory somewhere below the current SP that is not accessible (the
+ * memory that caused the signal). The signal handler works out the next
+ * accessible value of SP and passes this in r12. This code then sets up the SP
+ * to be this new value and calls the code to create and throw the stack overflow
+ * exception.
+ */
+ENTRY art_quick_throw_stack_overflow_from_signal
+ SETUP_SAVE_ALL_CALLEE_SAVE_FRAME // save all registers as basis for long jump context
+ mov r0, r9 @ pass Thread::Current
+ mov r1, sp @ pass SP
+ mov sp, r12 @ move SP down to below protected region.
+ b artThrowStackOverflowFromCode @ artThrowStackOverflowFromCode(Thread*, SP)
+END art_quick_throw_stack_overflow_from_signal
+
/*
* All generated callsites for interface invokes and invocation slow paths will load arguments
* as usual - except instead of loading arg0/r0 with the target Method*, arg0/r0 will contain