Re: [PATCH]: Fix PR19061, gdb hangs/spins-on-cpu when debugging any program on Alpha

[Simon Marchi <simon dot marchi at ericsson dot com>]

On 2017-12-15 07:11 AM, Uros Bizjak wrote:
> Hello!
> 
> Attached patch fixes PR19061, where gdb hangs/spins-on-cpu when
> debugging any program on Alpha. The patch is effectively a forward
> port of Richard's patch from the Comment #5 of the PR [1].
> 
> 
> 2017-12-15  Uros Bizjak  <ubizjak@gmail.com>
>         Richard Henderson  <rth@redhat.com>
> 
>     PR gdb/19061
>     * alpha-tdep.c (alpha_software_single_step): Call
>     alpha_deal_with_atomic_sequence here.
>     (set_gdbarch_software_single_step): Set to alpha_software_single_step.
>     * nat/linux-ptrace.h [__alpha__]: Define GDB_ARCH_IS_TRAP_BRKPT
>     and GDB_ARCH_IS_TRAP_HWBKPT.
> 
> Patch was tested on alphaev68-linux-gnu, also tested with gcc's
> testsuite, where it fixed all hangs in guality.exp and
> simulate-thread.exp testcases.
> 
> Please note that I have no commit access, so if approved, please
> commit the patch to the source repository for me. I also have
> functionally equivalent patch for gdb-8 branch which I plan to submit
> later.
> 
> [1] https://sourceware.org/bugzilla/show_bug.cgi?id=19061#c5
> 
> Uros.
> 

Hi Uros and Richard,

I would need your input.  Using this cross-compiler:

alphaev67-unknown-linux-gnu-gcc (crosstool-NG crosstool-ng-1.22.0-677-ga3dd55b9) 6.3.0
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I get this error:

  CXX    linux-nat.o
/home/simark/src/binutils-gdb/gdb/linux-nat.c: In function 'void save_stop_reason(lwp_info*)':
/home/simark/src/binutils-gdb/gdb/linux-nat.c:2718:9: error: duplicated 'if' condition [-Werror=duplicated-cond]
    else if (GDB_ARCH_IS_TRAP_HWBKPT (siginfo.si_code))
         ^~
In file included from /home/simark/src/binutils-gdb/gdb/linux-nat.c:31:0:
/home/simark/src/binutils-gdb/gdb/nat/linux-ptrace.h:173:41: note: previously used here
 # define GDB_ARCH_IS_TRAP_BRKPT(X) ((X) == TRAP_BRKPT)
                                    ~~~~~^~~~~~~~~~~~~~
/home/simark/src/binutils-gdb/gdb/linux-nat.c:2709:13: note: in expansion of macro 'GDB_ARCH_IS_TRAP_BRKPT'
    else if (GDB_ARCH_IS_TRAP_BRKPT (siginfo.si_code))
             ^~~~~~~~~~~~~~~~~~~~~~

Does Alpha even have hardware breakpoints?  If not, I would suggest
defining GDB_ARCH_IS_TRAP_HWBKPT to 0 for __alpha__.  It would get
rid of the error, and be more exact (no si_code can mean "hardware
breakpoint" on alpha).

Simon