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

[John Baldwin <jhb@FreeBSD.org>]

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.

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?

 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.

> @@ -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;`

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

-- 
John Baldwin