[Bug gas/21999] New: ARM: relative conditional movw/movt pairs may use incorrect offset

[ard.biesheuvel at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=21999

            Bug ID: 21999
           Summary: ARM: relative conditional movw/movt pairs may use
                    incorrect offset
           Product: binutils
           Version: 2.30 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: ard.biesheuvel at linaro dot org
  Target Milestone: ---

The following code

        .syntax unified
        .thumb
        movw    r0, #:lower16:foo - (1f + 4)
        movt    r0, #:upper16:foo - (1f + 4)
1:      add     r0, r0, pc

        movweq  r0, #:lower16:foo - (1f + 4)
        movteq  r0, #:upper16:foo - (1f + 4)
1:      addeq   r0, r0, pc

        ittt    eq
        movweq  r0, #:lower16:foo - (1f + 4)
        movteq  r0, #:upper16:foo - (1f + 4)
1:      addeq   r0, r0, pc

assembled for ARMv7 in Thumb2 mode produces the following when using
-mimplicit-it=always

   0:   f64f 70f4       movw    r0, #65524      ; 0xfff4
   4:   f6cf 70f8       movt    r0, #65528      ; 0xfff8
   8:   4478            add     r0, pc
   a:   bf04            itt     eq
   c:   f64f 70f4       movweq  r0, #65524      ; 0xfff4
  10:   f6cf 70f8       movteq  r0, #65528      ; 0xfff8
  14:   bf08            it      eq
  16:   4478            addeq   r0, pc
  18:   bf02            ittt    eq
  1a:   f64f 70f4       movweq  r0, #65524      ; 0xfff4
  1e:   f6cf 70f8       movteq  r0, #65528      ; 0xfff8
  22:   4478            addeq   r0, pc

Note that the addend is incorrect for the second case: it does not take the
additional 'it' instruction in account.

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