https://bugs.llvm.org/show_bug.cgi?id=45064
Bug ID: 45064
Summary: [WinEH] LLVM emits unreachable (incorrect?) RSP
adjustments after noreturn calls, like
CxxThrowException
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: r...@google.com
CC: craig.top...@gmail.com, h...@chromium.org,
llvm-bugs@lists.llvm.org, llvm-...@redking.me.uk,
spatel+l...@rotateright.com
I noticed this while investigating https://bugs.llvm.org/show_bug.cgi?id=45021
We've had this bug many times:
https://bugs.llvm.org/show_bug.cgi?id=43155
https://bugs.llvm.org/show_bug.cgi?id=27117
But we still have it. :)
Consider, with EH enabled:
struct MakeCleanup {
~MakeCleanup();
};
bool cond();
void foo() {
MakeCleanup o;
if (cond())
throw;
if (cond())
throw;
}
We get this:
...
callq _CxxThrowException
subq $32, %rsp
.Ltmp7:
jmp .LBB0_8
.LBB0_5: # %if.then3
.Ltmp4:
xorl %ecx, %ecx
xorl %edx, %edx
callq _CxxThrowException
subq $32, %rsp
.Ltmp5:
.LBB0_8: # %unreachable
This is worrying to me, because it could interfere with the Win64 stack
unwinder.
On Win64, most stack frames are reserved, and I think the code we added in the
first place is causing more trouble than it's worth:
if (CLI.DoesNotReturn && !getTargetMachine().Options.TrapUnreachable) {
// No need to reset the stack after the call if the call doesn't return. To
// make the MI verify, we'll pretend the callee does it for us.
NumBytesForCalleeToPop = NumBytes;
}
X86ISelLowering.cpp:4333 (file is too big to link on github)
When EH is involved, it becomes difficult for the code I added to PEI to
determine that this adjustment is after a noreturn function call:
https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86FrameLowering.cpp#L3074
I think we might want to invent a cleaner way of indicating that the adjustment
is "dead" and can be skipped while still pacifying the verifier. I notice that
a third argument to ADJCALLSTACKDOWN* was added to pacify the verifier, so we
could do the same again for ADJCALLSTACKUP*.
--
You are receiving this mail because:
You are on the CC list for the bug._______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
