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/compiler/dex/quick/arm/call_arm.cc b/compiler/dex/quick/arm/call_arm.cc
index 163c0fe..d3477c9 100644
--- a/compiler/dex/quick/arm/call_arm.cc
+++ b/compiler/dex/quick/arm/call_arm.cc
@@ -360,6 +360,22 @@
if (Runtime::Current()->ExplicitStackOverflowChecks()) {
/* Load stack limit */
Load32Disp(rs_rARM_SELF, Thread::StackEndOffset<4>().Int32Value(), rs_r12);
+ } else {
+ // Implicit stack overflow check.
+ // Generate a load from [sp, #-overflowsize]. If this is in the stack
+ // redzone we will get a segmentation fault.
+ //
+ // Caveat coder: if someone changes the kStackOverflowReservedBytes value
+ // we need to make sure that it's loadable in an immediate field of
+ // a sub instruction. Otherwise we will get a temp allocation and the
+ // code size will increase.
+ //
+ // This is done before the callee save instructions to avoid any possibility
+ // of these overflowing. This uses r12 and that's never saved in a callee
+ // save.
+ OpRegRegImm(kOpSub, rs_r12, rs_rARM_SP, Thread::kStackOverflowReservedBytes);
+ Load32Disp(rs_r12, 0, rs_r12);
+ MarkPossibleStackOverflowException();
}
}
/* Spill core callee saves */
@@ -418,17 +434,8 @@
AddSlowPath(new(arena_)StackOverflowSlowPath(this, branch, false, frame_size_));
}
} else {
- // Implicit stack overflow check.
- // Generate a load from [sp, #-overflowsize]. If this is in the stack
- // redzone we will get a segmentation fault.
- //
- // Caveat coder: if someone changes the kStackOverflowReservedBytes value
- // we need to make sure that it's loadable in an immediate field of
- // a sub instruction. Otherwise we will get a temp allocation and the
- // code size will increase.
- OpRegRegImm(kOpSub, rs_r12, rs_rARM_SP, Thread::kStackOverflowReservedBytes);
- Load32Disp(rs_r12, 0, rs_r12);
- MarkPossibleStackOverflowException();
+ // Implicit stack overflow check has already been done. Just make room on the
+ // stack for the frame now.
OpRegImm(kOpSub, rs_rARM_SP, frame_size_without_spills);
}
} else {