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Avoid non-C++-enabled babeltrace versions

Message ID m3twinuxbs.fsf@oc1027705133.ibm.com
State New
Headers show

Commit Message

Andreas Arnez April 27, 2016, 11:04 a.m. UTC
In some babeltrace versions before 1.2.0, the header file iterator.h is
not fully enabled for use from C++, since it contains an anonymous enum
in a struct declaration.  This is fixed in later babeltrace versions:

  https://lists.lttng.org/pipermail/lttng-dev/2013-September/021411.html

Now that GDB is compiled with C++, the GDB build fails on a system with
such a babeltrace version: the compiler complains about a missing
declaration of BT_SEEK_BEGIN in ctf.c.

This patch enhances the configure check to recognize such babeltrace
versions as unusable for GDB.

gdb/ChangeLog:

	* configure.ac: Enhance configure check for babeltrace to reject
	non-C++-enabled versions.
	* configure: Regenerate.
---
 gdb/configure    | 1 +
 gdb/configure.ac | 1 +
 2 files changed, 2 insertions(+)

Comments

Pedro Alves April 27, 2016, 12:02 p.m. UTC | #1
On 04/27/2016 12:04 PM, Andreas Arnez wrote:
> In some babeltrace versions before 1.2.0, the header file iterator.h is
> not fully enabled for use from C++, since it contains an anonymous enum
> in a struct declaration.  This is fixed in later babeltrace versions:
> 
>   https://lists.lttng.org/pipermail/lttng-dev/2013-September/021411.html
> 

The rationale for that commit is actually wrong.  There's nothing 
wrong with anonymous enums in structs in C++, and being anonymous is
actually irrelevant.   The problem is that a struct/class establishes a scope
in C++, but not in C.  So outside the struct, to refer to the enum values,
you'd have to write bt_iter_pos::BT_SEEK_TIME etc.

Anyway ...

> Now that GDB is compiled with C++, the GDB build fails on a system with
> such a babeltrace version: the compiler complains about a missing
> declaration of BT_SEEK_BEGIN in ctf.c.
> 
> This patch enhances the configure check to recognize such babeltrace
> versions as unusable for GDB.
> 
> gdb/ChangeLog:
> 
> 	* configure.ac: Enhance configure check for babeltrace to reject
> 	non-C++-enabled versions.
> 	* configure: Regenerate.

OK.

Thanks,
Pedro Alves
Andreas Arnez April 27, 2016, 2:24 p.m. UTC | #2
On Wed, Apr 27 2016, Pedro Alves wrote:

> On 04/27/2016 12:04 PM, Andreas Arnez wrote:
>> In some babeltrace versions before 1.2.0, the header file iterator.h is
>> not fully enabled for use from C++, since it contains an anonymous enum
>> in a struct declaration.  This is fixed in later babeltrace versions:
>> 
>>   https://lists.lttng.org/pipermail/lttng-dev/2013-September/021411.html
>> 
>
> The rationale for that commit is actually wrong.  There's nothing 
> wrong with anonymous enums in structs in C++, and being anonymous is
> actually irrelevant.   The problem is that a struct/class establishes a scope
> in C++, but not in C.  So outside the struct, to refer to the enum values,
> you'd have to write bt_iter_pos::BT_SEEK_TIME etc.

Right, the enum being anonymous does not cause a problem by itself.
Changed the commit message to avoid that impression.

>
> Anyway ...
>
>> Now that GDB is compiled with C++, the GDB build fails on a system with
>> such a babeltrace version: the compiler complains about a missing
>> declaration of BT_SEEK_BEGIN in ctf.c.
>> 
>> This patch enhances the configure check to recognize such babeltrace
>> versions as unusable for GDB.
>> 
>> gdb/ChangeLog:
>> 
>> 	* configure.ac: Enhance configure check for babeltrace to reject
>> 	non-C++-enabled versions.
>> 	* configure: Regenerate.
>
> OK.

Thanks, pushed after adjusting the commit message.

--
Andreas
diff mbox

Patch

diff --git a/gdb/configure b/gdb/configure
index 3cf95e7..228cb99 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -16390,6 +16390,7 @@  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;
 
+			pos.type = BT_SEEK_BEGIN;
 			bt_iter_set_pos (bt_ctf_get_iter (NULL), pos);
 			scope = bt_ctf_get_top_level_scope (event,
 			      				   BT_STREAM_EVENT_HEADER);
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 70452d3..3aa132a 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -2286,6 +2286,7 @@  else
 			struct bt_ctf_event *event = NULL;
 			const struct bt_definition *scope;
 
+			pos.type = BT_SEEK_BEGIN;
 			bt_iter_set_pos (bt_ctf_get_iter (NULL), pos);
 			scope = bt_ctf_get_top_level_scope (event,
 			      				   BT_STREAM_EVENT_HEADER);