Re: [patch] Fix --with-babeltrace with gcc-4.9.1

[Doug Evans <dje@google.com>]

On Mon, Aug 4, 2014 at 1:29 PM, Jan Kratochvil
<jan.kratochvil@redhat.com> wrote:
> Hi,
>
> when I tried to use --with-babeltrace on Fedora Rawhide x86_64
> using gcc-4.9.1-3.fc22.x86_64 I got:
>
> checking for libbabeltrace... no
> configure: error: babeltrace is missing or unusable
> Makefile:7973: recipe for target 'configure-gdb' failed
>
> configure:15890: checking for libbabeltrace
> configure:15918: gcc -o conftest -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic   -Werror   -static-libstdc++ -static-libgcc -Wl,-z,relro    conftest.c -lselinux -lncurses -lz -lm  -ldl   /usr/lib64/libbabeltrace.so /usr/lib64/libbabeltrace-ctf.so >&5
> conftest.c: In function 'main':
> conftest.c:198:21: error: unused variable 'pos' [-Werror=unused-variable]
>  struct bt_iter_pos *pos = bt_iter_get_pos (bt_ctf_get_iter (NULL));
>                      ^
> cc1: all warnings being treated as errors
> configure:15918: $? = 1
> configure: failed program was:
>
> The patch below fixes it for me.
>
> In configure.ac there is above this check:
>   # Append -Werror to CFLAGS so that configure can catch the warning
>   # "assignment from incompatible pointer type", which is related to
>   # the babeltrace change from 1.0.3 to 1.1.0.  Babeltrace 1.1.0 works
>   # in GDB, while babeltrace 1.0.3 is broken.
>   # AC_LIB_HAVE_LINKFLAGS may modify CPPFLAGS in it, so it should be
>   # safe to save and restore CFLAGS here.
>   saved_CFLAGS=$CFLAGS
>   CFLAGS="$CFLAGS -Werror"
>
> Maybe it would be easier to use there:
>   CFLAGS="$CFLAGS -Werror -Wno-unused-variable"
>
> But maybe -Werror is cross-compiler compatible while -Wno-unused-variable is
> not, I have no idea.
>
>
> Jan
>
> gdb/
> 2014-08-04  Jan Kratochvil  <jan.kratochvil@redhat.com>
>
>         * configure.ac (--with-babeltrace): Use 'pos'.
>         * configure: Regenerate.
>
> diff --git a/gdb/configure.ac b/gdb/configure.ac
> index 70d0964..07d2f00 100644
> --- a/gdb/configure.ac
> +++ b/gdb/configure.ac
> @@ -2437,6 +2437,7 @@ else
>                         struct bt_ctf_event *event = NULL;
>                         const struct bt_definition *scope;
>
> +                       (void) pos; /* Prevent -Werror=unused-variable.  */
>                         scope = bt_ctf_get_top_level_scope (event,
>                                                            BT_STREAM_EVENT_HEADER);
>                         bt_ctf_get_uint64 (bt_ctf_get_field (event, scope, "id"));
> diff --git a/gdb/configure b/gdb/configure
> index 809326a..b983d16 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -15344,6 +15344,7 @@ struct bt_iter_pos *pos = bt_iter_get_pos (bt_ctf_get_iter (NULL));
>                         struct bt_ctf_event *event = NULL;
>                         const struct bt_definition *scope;
>
> +                       (void) pos; /* Prevent -Werror=unused-variable.  */
>                         scope = bt_ctf_get_top_level_scope (event,
>                                                            BT_STREAM_EVENT_HEADER);
>                         bt_ctf_get_uint64 (bt_ctf_get_field (event, scope, "id"));
>

I don't know enough about babeltrace to say whether we can just remove
pos altogether.
I'm happy with the patch as is though.