ARC: Ignore ptrace SETREGSET request for synthetic register "stop_pc"

ARCompact TRAP_S insn used for breakpoints, commits before exception is
taken (updating architectural PC). So ptregs->ret contains next-PC and
not the breakpoint PC itself. This is different from other restartable
exceptions such as TLB Miss where ptregs->ret has exact faulting PC.
gdb needs to know exact-PC hence ARC ptrace GETREGSET provides for
@stop_pc which returns ptregs->ret vs. EFA depending on the
situation.

However, writing stop_pc (SETREGSET request), which updates ptregs->ret
doesn't makes sense stop_pc doesn't always correspond to that reg as
described above.

This was not an issue so far since user_regs->ret / user_regs->stop_pc
had same value and both writing to ptregs->ret was OK, needless, but NOT
broken, hence not observed.

With gdb "jump", they diverge, and user_regs->ret updating ptregs is
overwritten immediately with stop_pc, which this patch fixes.

Reported-by: Anton Kolesov <akolesov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

diff --git a/arch/arc/kernel/ptrace.c b/arch/arc/kernel/ptrace.c
index 3332385..5d76706 100644 (file)
--- a/arch/arc/kernel/ptrace.c
+++ b/arch/arc/kernel/ptrace.c
@@ -102,7 +102,7 @@ static int genregs_set(struct task_struct *target,
        REG_IGNORE_ONE(pad2);
        REG_IN_CHUNK(callee, efa, cregs);       /* callee_regs[r25..r13] */
        REG_IGNORE_ONE(efa);                    /* efa update invalid */
-       REG_IN_ONE(stop_pc, &ptregs->ret);      /* stop_pc: PC update */
+       REG_IGNORE_ONE(stop_pc);                        /* PC updated via @ret */
 
        return ret;
 }