[llvm-bugs] [Bug 37225] New: [x86] __builtin_writeeflags_u32/__builtin_readeflags_u32 should not be available in 64-bit mode

via llvm-bugs llvm-bugs at lists.llvm.org
Tue Apr 24 13:50:49 PDT 2018


            Bug ID: 37225
           Summary: [x86]
                    should not be available in 64-bit mode
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: craig.topper at gmail.com
                CC: llvm-bugs at lists.llvm.org

The backend cannot isel these correctly and probably shouldn't try. For the
writeeflags we won't have enough input data to write the whole 64-bit RFLAGS
register. This would fine in CPL 3 where the upper bits aren't writable. But in
CPL 0 the bits are writable so we need to ensure the user provided enough bits.

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