Bug #7756: clang 4.2 sees through UNINITIALIZED_VAR macro, gives warning

• Status: Closed
• Assignee: mame (Yusuke Endoh)
• Target version: 2.6
• ruby -v: -

[drbrain (Eric Hodel)]

=begin

In clang 3.2, the UNINITIALIZED_VAR macro does not prevent the compiler from producing a warning.

Apple clang 3.2:

$ clang -v
Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.2.1
Thread model: posix

When compiling thread.c:

compiling ../trunk/thread.c
../trunk/thread.c:3261:34: warning: variable 'orig_read' is uninitialized when
used within its own initialization [-Wuninitialized]
rb_fdset_t UNINITIALIZED_VAR(orig_read);
^~~~~~~~~
../trunk/vm_core.h:119:34: note: expanded from macro 'UNINITIALIZED_VAR'
#define UNINITIALIZED_VAR(x) x = x
^
../trunk/thread.c:3262:34: warning: variable 'orig_write' is uninitialized when
used within its own initialization [-Wuninitialized]
rb_fdset_t UNINITIALIZED_VAR(orig_write);
^~~~~~~~~~
../trunk/vm_core.h:119:34: note: expanded from macro 'UNINITIALIZED_VAR'
#define UNINITIALIZED_VAR(x) x = x
^
../trunk/thread.c:3263:34: warning: variable 'orig_except' is uninitialized when
used within its own initialization [-Wuninitialized]
rb_fdset_t UNINITIALIZED_VAR(orig_except);
^~~~~~~~~~~
../trunk/vm_core.h:119:34: note: expanded from macro 'UNINITIALIZED_VAR'
#define UNINITIALIZED_VAR(x) x = x
^
3 warnings generated.

=end

[kosaki (Motohiro KOSAKI)]

Hm, maybe we need another workaround.
Does attribute (unused) works on your compiler?

likes

#ifdef GNUC
#define UNINITIALIZED_VAR(x) x attribute (unused) = x
#else
....

[drbrain (Eric Hodel)]

=begin
This patch works:

Index: vm_core.h

--- vm_core.h (revision 38980)
+++ vm_core.h (working copy)
@@ -116,7 +116,7 @@
#endif /* GNUC >= 3 */

#if GNUC >= 3
-#define UNINITIALIZED_VAR(x) x = x
+#define UNINITIALIZED_VAR(x) x attribute((unused))
#else
#define UNINITIALIZED_VAR(x) x
#endif
=end

[ko1 (Koichi Sasada)]

• Assignee set to mame (Yusuke Endoh)

mame-san, how about it?

[mame (Yusuke Endoh)]

• Target version changed from 2.0.0 to 2.6

It emits just a warning, not an error, right?
Looks not significant.

--
Yusuke Endoh [e-mail]

[drbrain (Eric Hodel)]

It is only a warning

[nobu (Nobuyoshi Nakada)]

=begin
Unfortunately, it doesn't shut up gcc-4.7.

thread.c: In function 'do_select':
thread.c:3155:26: warning: 'orig_except.fdset' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3352:16: note: 'orig_except.fdset' was declared here
thread.c:3229:19: warning: 'orig_except.maxfd' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3352:16: note: 'orig_except.maxfd' was declared here
thread.c:3155:26: warning: 'orig_write.fdset' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3351:16: note: 'orig_write.fdset' was declared here
thread.c:3229:19: warning: 'orig_write.maxfd' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3351:16: note: 'orig_write.maxfd' was declared here
thread.c:3155:26: warning: 'orig_read.fdset' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3350:16: note: 'orig_read.fdset' was declared here
thread.c:3229:19: warning: 'orig_read.maxfd' may be used uninitialized in this function [-Wmaybe-uninitialized]
thread.c:3350:16: note: 'orig_read.maxfd' was declared here
=end

[naruse (Yui NARUSE)]

GCC 4.6 and clang (2.8?) supports pragma diagnostic, but its syntax is different from current UNINITIALIZED_VAR().

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
blah blah
#pragma GCC diagnostic pop

http://gcc.gnu.org/gcc-4.6/changes.html
http://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html
http://clang.llvm.org/docs/UsersManual.html#controlling-diagnostics-via-pragmas

[naruse (Yui NARUSE)]

A macro can be following, but it still changes syntax from current UNINITIALIZED_VAR.

#if GCC_VERSION_SINCE(4,6,0) || defined(clang)

define SUPPRESS_DIAGNOSTIC(arg,rest) \

    _Pragma("GCC diagnostic push") \
    _Pragma(STRINGIZE(GCC diagnostic ignored arg)) \
    rest \
    _Pragma("GCC diagnostic pop")

#else

define SUPPRESS_DIAGNOSTIC(arg,rest) rest

#endif

[nobu (Nobuyoshi Nakada)]

• Subject changed from clang 3.2 sees through UNINITIALIZED_VAR macro, gives warning to clang 4.2 sees through UNINITIALIZED_VAR macro, gives warning

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r39855.
Eric, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

vm_core.h: suppress warnings

• vm_core.h (UNINITIALIZED_VAR): suppress warnings by clang 4.2.
  [ruby-core:51742] [Bug #7756]