[Bug tdep/27525] New: powerpc: displaced stepping broken for breakpoint at lnia instruction

[Bug tdep/27525] New: powerpc: displaced stepping broken for breakpoint at lnia instruction

[gabriel at inconstante dot net.br]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

            Bug ID: 27525
           Summary: powerpc: displaced stepping broken for breakpoint at
                    lnia instruction
           Product: gdb
           Version: unknown
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: gabriel at inconstante dot net.br
                CC: pedromfc at linux dot ibm.com, rcardoso at linux dot vnet.ibm.com
  Target Milestone: ---

Consider the following function:

.global fn
.type fn,@function
fn:
    lnia   3
    blr

If I place a breakpoing at 'fn', then try to 'stepi', the result in 'r3' is not
set to the address of the next instruction, as can be seen in the following
output snippet:

Breakpoint 1, 0x0000000010000680 in fn ()
>>> set displaced-stepping on
>>> x /i $pc
=> 0x10000680 <fn>:     lnia    r3
>>> stepi
0x0000000010000684 in fn ()
>>> info registers r3
r3             0x100004ac          268436652

However, pedromfc told me that disabling displaced stepping would probably fix
the problem, and it did, indeed:

Breakpoint 1, 0x0000000010000680 in fn ()
>>> set displaced-stepping off
>>> x /i $pc
=> 0x10000680 <fn>:     lnia    r3
>>> stepi
0x0000000010000684 in fn ()
>>> info registers r3
r3             0x10000684          268437124

Cheers,
Gabriel

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[pedromfc at linux dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

Pedro Franco de Carvalho <pedromfc at linux dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ulrich.weigand at de dot ibm.com

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[will_schmidt at vnet dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

Will Schmidt <will_schmidt at vnet dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |will_schmidt at vnet dot ibm.com

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Will Schmidt <willschm@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=e3d528d7e6a6b863d30aaecf74adf8c78286f84c

commit e3d528d7e6a6b863d30aaecf74adf8c78286f84c
Author: Will Schmidt <will_schmidt@vnet.ibm.com>
Date:   Mon Apr 12 13:35:54 2021 -0500

    [PATCH, rs6000, v3][PR gdb/27525] displaced stepping across addpcis/lnia.

      This addresses PR gdb/27525.     The lnia and other variations
    of the addpcis instruction write the value of the NIA into a target
register.
    If we are single-stepping across a breakpoint, the instruction is executed
    from a displaced location, and thusly the written value of the PC/NIA
    will be incorrect.   The changes here will measure the displacement
    offset, and adjust the target register value to compensate.

    YYYY-MM-DD  Will Schmidt  <will_schmidt@vnet.ibm.com>

    gdb/ChangeLog:

            * rs6000-tdep.c (ppc_displaced_step_fixup): Update to handle
            the addpcis/lnia instruction.

    gdb/testsuite/ChangeLog:

            * gdb.arch/powerpc-addpcis.exp: Testcase harness to
            exercise single-stepping over subpcis,lnia,addpcis instructions
            with displacement.
            * gdb.arch/powerpc-addpcis.s: Testcase with stream
            of addpcis/lnia/subpcis instructions.
            * gdb.arch/powerpc-lnia.exp: Testcase harness to exercise
            single-stepping over lnia instructions with displacement.
            * gdb.arch/powerpc-lnia.s: Testcase with stream of
            lnia instructions.

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[will_schmidt at vnet dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

--- Comment #2 from Will Schmidt <will_schmidt at vnet dot ibm.com> ---
This should be corrected by the patch I committed earlier today.

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[will_schmidt at vnet dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

Will Schmidt <will_schmidt at vnet dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at sourceware dot org   |will_schmidt at vnet dot ibm.com
             Status|NEW                         |ASSIGNED

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[Bug tdep/27525] powerpc: displaced stepping broken for breakpoint at lnia instruction

[will_schmidt at vnet dot ibm.com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27525

Will Schmidt <will_schmidt at vnet dot ibm.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Will Schmidt <will_schmidt at vnet dot ibm.com> ---
Resolved with the commit:
"
commit e3d528d7e6a6b863d30aaecf74adf8c78286f84c
Author: Will Schmidt <will_schmidt@vnet.ibm.com>
Date:   Mon Apr 12 13:35:54 2021 -0500

    [PATCH, rs6000, v3][PR gdb/27525] displaced stepping across addpcis/lnia.
"

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