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author | Bill Wendling <isanbard@gmail.com> | 2010-01-19 02:44:01 +0000 |
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committer | Bill Wendling <isanbard@gmail.com> | 2010-01-19 02:44:01 +0000 |
commit | e1e0f485f9721a0c4236326f32d0a48561a1af7a (patch) | |
tree | a5f258e56eb985580e41c7c7f28843c2e0830940 /lib/Target/PowerPC/PPCTargetMachine.cpp | |
parent | 6e3be14be4eadd9aefea654611c808eea9eb8aea (diff) | |
download | llvm-e1e0f485f9721a0c4236326f32d0a48561a1af7a.tar.gz llvm-e1e0f485f9721a0c4236326f32d0a48561a1af7a.tar.bz2 llvm-e1e0f485f9721a0c4236326f32d0a48561a1af7a.tar.xz |
Even more explanation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93841 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/PowerPC/PPCTargetMachine.cpp')
-rw-r--r-- | lib/Target/PowerPC/PPCTargetMachine.cpp | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/lib/Target/PowerPC/PPCTargetMachine.cpp b/lib/Target/PowerPC/PPCTargetMachine.cpp index c80a530c88..c7f788238a 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. |