[Lldb-commits] [PATCH] D88583: [lldb] [test/Register] Add read/write tests for x87 regs

Pavel Labath via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Thu Oct 1 05:32:20 PDT 2020

labath added a comment.

In D88583#2305815 <https://reviews.llvm.org/D88583#2305815>, @mgorny wrote:

> Fixed segfault when built with GCC and fixed my poor attempt to run FXSAVE with REX.W prefix. Now it correctly gets 64-bit FIP and FDP, though it's unclear whether the apparent truncation is a bug in LLDB writing it or some other kind of limitation.

I think that could be an architectural cpu limitation. IIUC, even though the addresses are nominally 64-bit, not all addresses within that space are actually usable -- only the topmost and bottommost XX GB (TB) of the address space are. It could be that the cpu does not actually store all of the bits of these registers, but rather just sign-extends the most significant usable bit.



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