From e1e0f485f9721a0c4236326f32d0a48561a1af7a Mon Sep 17 00:00:00 2001 From: Bill Wendling Date: Tue, 19 Jan 2010 02:44:01 +0000 Subject: [PATCH] Even more explanation. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93841 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/PowerPC/PPCTargetMachine.cpp | 12 ++++++++++++ lib/Target/X86/X86TargetMachine.cpp | 12 ++++++++++++ 2 files changed, 24 insertions(+) diff --git a/lib/Target/PowerPC/PPCTargetMachine.cpp b/lib/Target/PowerPC/PPCTargetMachine.cpp index c80a530c885..c7f788238a3 100644 --- a/lib/Target/PowerPC/PPCTargetMachine.cpp +++ b/lib/Target/PowerPC/PPCTargetMachine.cpp @@ -201,6 +201,18 @@ bool PPCTargetMachine::addSimpleCodeEmitter(PassManagerBase &PM, /// to bugs or other conditions. We will default to a 4-byte encoding unless the /// system tells us otherwise. /// +/// The issue is when the CIE says their is an LSDA. That mandates that every +/// FDE have an LSDA slot. But if the function does not need an LSDA. There +/// needs to be some way to signify there is none. The LSDA is encoded as +/// pc-rel. But you don't look for some magic value after adding the pc. You +/// have to look for a zero before adding the pc. The problem is that the size +/// of the zero to look for depends on the encoding. The unwinder bug in SL is +/// that it always checks for a pointer-size zero. So on x86_64 it looks for 8 +/// bytes of zero. If you have an LSDA, it works fine since the 8-bytes are +/// non-zero so it goes ahead and then reads the value based on the encoding. +/// But if you use sdata4 and there is no LSDA, then the test for zero gives a +/// false negative and the unwinder thinks there is an LSDA. +/// /// FIXME: This call-back isn't good! We should be using the correct encoding /// regardless of the system. However, there are some systems which have bugs /// that prevent this from occuring. diff --git a/lib/Target/X86/X86TargetMachine.cpp b/lib/Target/X86/X86TargetMachine.cpp index 684e1fc573d..445318e64fb 100644 --- a/lib/Target/X86/X86TargetMachine.cpp +++ b/lib/Target/X86/X86TargetMachine.cpp @@ -257,6 +257,18 @@ void X86TargetMachine::setCodeModelForJIT() { /// to bugs or other conditions. We will default to a 4-byte encoding unless the /// system tells us otherwise. /// +/// The issue is when the CIE says their is an LSDA. That mandates that every +/// FDE have an LSDA slot. But if the function does not need an LSDA. There +/// needs to be some way to signify there is none. The LSDA is encoded as +/// pc-rel. But you don't look for some magic value after adding the pc. You +/// have to look for a zero before adding the pc. The problem is that the size +/// of the zero to look for depends on the encoding. The unwinder bug in SL is +/// that it always checks for a pointer-size zero. So on x86_64 it looks for 8 +/// bytes of zero. If you have an LSDA, it works fine since the 8-bytes are +/// non-zero so it goes ahead and then reads the value based on the encoding. +/// But if you use sdata4 and there is no LSDA, then the test for zero gives a +/// false negative and the unwinder thinks there is an LSDA. +/// /// FIXME: This call-back isn't good! We should be using the correct encoding /// regardless of the system. However, there are some systems which have bugs /// that prevent this from occuring.