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Re: [Qemu-devel] Redundant redeclaration of 'gmtime_r' with mingw64

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] Redundant redeclaration of 'gmtime_r' with mingw64
Date: Tue, 22 Sep 2015 16:11:34 +0300

On Fri, Jun 05, 2015 at 03:38:21PM +0100, Stefan Hajnoczi wrote:
> Hi Stefan,
> I get the following compiler warning in Fedora 22
> (mingw32-headers-4.0.2-1.fc22):
> In file included from qemu/include/qemu-common.h:47:0,
>                  from qemu/include/qemu/timer.h:5,
>                  from qemu/include/sysemu/sysemu.h:8,
>                  from os-win32.c:34:
> qemu/include/sysemu/os-win32.h:77:12: warning: redundant redeclaration
> of 'gmtime_r' [-Wredundant-decls]
>  struct tm *gmtime_r(const time_t *timep, struct tm *result);
>             ^
> In file included from os-win32.c:30:0:
> /usr/i686-w64-mingw32/sys-root/mingw/include/time.h:272:107: note:
> previous definition of 'gmtime_r' was here
> QEMU has its own (non-reentrant) gmtime_r() and localtime_r()
> functions on Windows.  os-win32.h redefines the functions so the
> compiler is right to complain.
> I thought about adding qemu_gmtime_r() and qemu_localtime_r()
> functions to avoid the name clash.
> Do you have any new thoughts on this commit which introduced the
> os-win32.h definitions?
> commit d3e8f95753114a827f9cd8e819b1d5cc8333f76b
> Author: Stefan Weil <address@hidden>
> Date:   Sat Sep 22 22:26:19 2012 +0200
>     w32: Add implementation of gmtime_r, localtime_r
>     Those functions are missing in MinGW.
>     Some versions of MinGW-w64 include defines for gmtime_r and localtime_r.
>     Older versions of these macros are buggy (they return a pointer to a
>     static variable), therefore we don't want them. Newer versions are
>     similar to the code used here, but without the memset.
>     The implementation which is used here is not strictly reentrant,
>     but sufficiently good for QEMU on w32 or w64.
>     Signed-off-by: Stefan Weil <address@hidden>
>     address@hidden: added comment about locking]
>     Signed-off-by: Blue Swirl <address@hidden>

I tried this: it compiles, but then fails to link.

Signed-off-by: Michael S. Tsirkin <address@hidden>

diff --git a/include/sysemu/os-win32.h b/include/sysemu/os-win32.h
index 706d85a..74230e7 100644
--- a/include/sysemu/os-win32.h
+++ b/include/sysemu/os-win32.h
@@ -72,11 +72,17 @@
 #define sigsetjmp(env, savemask) setjmp(env)
 #define siglongjmp(env, val) longjmp(env, val)
+#ifdef gmtime_r
 /* Missing POSIX functions. Don't use MinGW-w64 macros. */
 #undef gmtime_r
 struct tm *gmtime_r(const time_t *timep, struct tm *result);
+#ifdef localtime_r
 #undef localtime_r
 struct tm *localtime_r(const time_t *timep, struct tm *result);
 static inline void os_setup_signal_handling(void) {}
diff --git a/util/oslib-win32.c b/util/oslib-win32.c
index 730a670..abd710a 100644
--- a/util/oslib-win32.c
+++ b/util/oslib-win32.c
@@ -95,6 +95,7 @@ void qemu_anon_ram_free(void *ptr, size_t size)
 /* FIXME: add proper locking */
 struct tm *gmtime_r(const time_t *timep, struct tm *result)
@@ -106,7 +107,9 @@ struct tm *gmtime_r(const time_t *timep, struct tm *result)
     return p;
 /* FIXME: add proper locking */
 struct tm *localtime_r(const time_t *timep, struct tm *result)
@@ -118,6 +121,7 @@ struct tm *localtime_r(const time_t *timep, struct tm 
     return p;
 void qemu_set_block(int fd)

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