verify usage [was: [libvirt] [PATCH 03/13] Rewrite virAtomic APIs using GLib's atomic ops code]

[Eric Blake]

On 07/19/2012 08:15 AM, Eric Blake wrote:
> 
> I'll have to see if I can come up with a solution in upstream gnulib
> that expands verify() in such a way that works with -Wnested-externs.
> 

I'm pushing this documentation aid, so that the next time this question
comes up, we have something to point to.

From 6c37e0a73c7c1b6fe6eac4d794e2e65791a2700d Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Fri, 20 Jul 2012 16:48:46 -0600
Subject: [PATCH] verify: document conflict with -Wnested-externs

Our implementation of verify() relies on nested extern declarations,
so it is incompatible with gcc < 4.6 coupled with -Wnested-externs
when used inside a function body.  But inside a function body, you
can always arrange to use verify_expr() instead, which is warning-free.

* lib/verify.h: Give hint about usage when gcc warnings are enabled.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog    |    3 +++
 lib/verify.h |    6 +++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/ChangeLog b/ChangeLog
index 2fa6fd5..69437c9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2012-07-20  Eric Blake  <address@hidden>

+       verify: document conflict with -Wnested-externs
+       * lib/verify.h: Give hint about usage when gcc warnings are enabled.
+
        maint.mk: forbid exit(-1)
        * top/maint.mk (sc_prohibit_magic_number_exit): Detect negatives.

diff --git a/lib/verify.h b/lib/verify.h
index cef14ad..0c320b1 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -125,7 +125,7 @@
        extern int (*dummy (void)) [sizeof (struct {...})];

    * GCC warns about duplicate declarations of the dummy function if
-     -Wredundant_decls is used.  GCC 4.3 and later have a builtin
+     -Wredundant-decls is used.  GCC 4.3 and later have a builtin
      __COUNTER__ macro that can let us generate unique identifiers for
      each dummy function, to suppress this warning.

@@ -133,6 +133,10 @@
      which do not support _Static_assert, also do not warn about the
      last declaration mentioned above.

+   * GCC warns if -Wnested-externs is enabled and verify() is used
+     within a function body; but inside a function, you can always
+     arrange to use verify_expr() instead.
+
    * In C++, any struct definition inside sizeof is invalid.
      Use a template type to work around the problem.  */

-- 
1.7.10.4



-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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