[lldb-dev] [Bug 32986] New: Incorrect ROR_C implementation.

via lldb-dev lldb-dev at lists.llvm.org
Wed May 10 03:23:02 PDT 2017


            Bug ID: 32986
           Summary: Incorrect ROR_C implementation.
           Product: lldb
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: lldb-dev at lists.llvm.org
          Reporter: andrea at inversepath.com
                CC: llvm-bugs at lists.llvm.org


It appears that the ROR_C function, within the common utilities for the
ARM/Thumb Instruction Set Architecture, is incorrectly implemented.

>From lldb/source/Plugins/Process/Utility/ARMUtils.h:

static inline uint32_t ROR_C(const uint32_t value, const uint32_t amount,
                             uint32_t &carry_out, bool *success) {
  carry_out = Bit32(value, 31);

However according to the ARMv6-M Architecture Reference Manual (page A2-34)
ROR_C is implemented as follows in relation to the carry_out:

 m = shift MOD N;
 result = LSR(x,m) OR LSL(x,N-m);
 carry_out = result<N-1>;

Therefore I believe that the ROR_C function in ARMUtils.h should use the
result, rather than the value, when setting carry_out:

  carry_out = Bit32(result, 31);

A comparable fix was effective in passing tests in another project I


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