Re: [PATCH] fbsd-nat: Pacify gcc with no functional changes

[Enze Li <enze.li@hotmail.com>]

On Sat, Sep 09 2023 at 09:49:40 AM -0700, John Baldwin wrote:

> On 9/9/23 6:50 AM, Enze Li wrote:
>> I see these errors on FreeBSD/aarch64 when using gcc 12 without passing
>> --disable-werror.
>> =====================================================================
>>    CXX    fbsd-nat.o
>> fbsd-nat.c: In member function 'void fbsd_nat_target::resume_one_process(ptid_t, int, gdb_signal)':
>> fbsd-nat.c:1208:11: error: unused variable 'request' [-Werror=unused-variable]
>>   1208 |       int request;
>>        |           ^~~~~~~
>> fbsd-nat.c: In member function 'virtual ptid_t
>> fbsd_nat_target::wait(ptid_t, target_waitstatus*,
>> target_wait_flags)':
>> fbsd-nat.c:1726:22: error: declaration of 'inf' shadows a previous
>> local [-Werror=shadow=compatible-local]
>>   1726 |       for (inferior *inf : all_non_exited_inferiors (this))
>>        |                      ^~~
>> fbsd-nat.c:1697:17: note: shadowed declaration is here
>>   1697 |       inferior *inf = find_inferior_ptid (this, wptid);
>>        |                 ^~~
>> fbsd-nat.c: In member function 'virtual void
>> fbsd_nat_target::detach(inferior*, int)':
>> fbsd-nat.c:2044:18: error: variable 'wptid' set but not used
>> [-Werror=unused-but-set-variable]
>>   2044 |           ptid_t wptid = wait_1 (ptid, &ws, 0);
>>        |                  ^~~~~
>> cc1plus: all warnings being treated as errors
>> =====================================================================
>> This patch includes the following non-functional changes,
>> 1. Remove unused variable "request".
>> 2. Rename inf to inf_p to avoid shadowed declaration warnings.
>> 3. Set wptid to null_ptid when USE_SIGTRAP_SIGINFO is not defined.

Hi John,

Thanks for your review.

>
> I'm surprised you see this third warning.  USE_SIGTRAP_SIGINFO should
> be on for all modern versions of FreeBSD.  In particular, fbsd-nat.h
> enables it on 11.3 and later.  What version of FreeBSD are you
> building on?

I just realized that the third description is incorrect and should be:

  "3. Set wptid to null_ptid when USE_SIGTRAP_SIGINFO is defined."

BTW, I'm using FreeBSD/aarch64 13.2-RELEASE.

>
> From fbsd-nat.h:
>
> /* FreeBSD kernels 11.3 and later report valid si_code values for
>    SIGTRAP on all architectures.  Older FreeBSD kernels that supported
>    TRAP_BRKPT did not report valid values for MIPS and sparc64.  Even
>    older kernels without TRAP_BRKPT support did not report valid
>    values on any architecture.  */
> #if (__FreeBSD_kernel_version >= 1102502) || (__FreeBSD_version >= 1102502)
> # define USE_SIGTRAP_SIGINFO
>
>
>> Tested on FreeBSD/aarch64 by rebuilding.
>> ---
>>   gdb/fbsd-nat.c | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>> diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
>> index 0ee3bccb5ef..af416557504 100644
>> --- a/gdb/fbsd-nat.c
>> +++ b/gdb/fbsd-nat.c
>> @@ -1205,8 +1205,6 @@ fbsd_nat_target::resume_one_process (ptid_t ptid, int step,
>>       for (thread_info *tp : inf->non_exited_threads ())
>>       {
>> -      int request;
>> -
>>         /* If ptid is a specific LWP, suspend all other LWPs in the
>>   	 process, otherwise resume all LWPs in the process..  */
>>         if (!ptid.lwp_p() || tp->ptid.lwp () == ptid.lwp ())
>
> Thanks.  This a leftover from my recent patches, not sure why clang
> didn't notice.
>
>> @@ -1694,9 +1692,9 @@ fbsd_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
>>   	  || ourstatus->kind () == TARGET_WAITKIND_NO_RESUMED)
>>   	break;
>>   -      inferior *inf = find_inferior_ptid (this, wptid);
>> -      gdb_assert (inf != nullptr);
>> -      fbsd_inferior *fbsd_inf = get_fbsd_inferior (inf);
>> +      inferior *inf_p = find_inferior_ptid (this, wptid);
>> +      gdb_assert (inf_p != nullptr);
>> +      fbsd_inferior *fbsd_inf = get_fbsd_inferior (inf_p);
>>         gdb_assert (fbsd_inf != nullptr);
>>         gdb_assert (fbsd_inf->resumed_lwps != null_ptid);
>>         gdb_assert (fbsd_inf->running_lwps > 0);
>
> I might call this variable `winf` to match the `wptid` vs `ptid` pattern.
>

Fixed.

>> @@ -2094,6 +2092,9 @@ fbsd_nat_target::detach (inferior *inf, int from_tty)
>>   			  }
>>   		      }
>>   		  }
>> +#else
>> +		  /* pacify gcc  */
>> +		  wptid = null_ptid;
>
> Probably the better way to pacify this is to use a (void) cast to mark it
> as used, e.g. `(void)null_ptid;`
>

Okey, fixed.  I'll send v2 to the list soon.

Best Regards,
Enze

>>   #endif
>>   		  sig = 0;
>>   		  break;
>> base-commit: 38a984fa440c7686c741b7804eae06a528849aa7