OpenJDK fails to build with GCC when the #include<time.h> inside zip.cpp comes from a non-sysroot path

[Patrick Zhang]

Hi Florian

Thanks for your comments

>> I doubt it has anything to do with a sysroot vs non-sysroot configuration.

The tests are done on two systems respectively, CentOS 7.4 (glibc 2.17) and Fedora 28 (glibc 2.27). 
GCC 9 can be used as well to reproduce the issue as well like this:
1. /opt/gcc900/bin/g++ -c timetest.cpp
2. /opt/gcc900/bin/g++ -I<another-root>/usr/include -c timetest.cpp
3. /opt/gcc900/bin/g++ --sysroot=<another-root> -c timetest.cpp
4. /opt/gcc900/bin/g++ --sysroot=<another-root> -I/usr/include -c  timetest.cpp 
In above experiments, #1, #3 are good, because the time.h they found are under their sysroot path and treated as system header file (linemarker 3), while #2, #4 are bad since time.h comes from a non-sysroot path.

>> the comment in the OpenJDK is wrong and the declaration is included even on non-Solaris systems.

yes, the macro _REENTRANT is not specific for solaris system, instead it is for generic linux and gcc environment
See jdk/make/autoconf/flags-cflags.m4
if test "x$OPENJDK_TARGET_OS" = xlinux; then
  CFLAGS_OS_DEF_JVM="-DLINUX"
  CFLAGS_OS_DEF_JDK="-D_GNU_SOURCE -D_REENTRANT -D_LARGEFILE64_SOURCE"

if test "x$TOOLCHAIN_TYPE" = xgcc; then
  ALWAYS_DEFINES_JVM="-D_GNU_SOURCE -D_REENTRANT"

>> so replicating the declaration from <time.h> is a losing battle.

Agree, as the declaration may be a redundant one in most occasions, what about changing it like below? I tested in my env it works well.

diff -r 70a423caee44 src/share/native/com/sun/java/util/jar/pack/zip.cpp
--- a/src/share/native/com/sun/java/util/jar/pack/zip.cpp	Tue Oct 09 08:33:33 2018 +0100
+++ b/src/share/native/com/sun/java/util/jar/pack/zip.cpp	Wed Nov 28 22:13:12 2018 -0500
@@ -415,9 +415,7 @@
     ((uLong)h << 11) | ((uLong)m << 5) | ((uLong)s >> 1);
 }
 
-#ifdef _REENTRANT // solaris
-extern "C" struct tm *gmtime_r(const time_t *, struct tm *);
-#else
+#if !defined(_REENTRANT) // linux
 #define gmtime_r(t, s) gmtime(t)
 #endif
 /*


>> Which system needs the gmtime_r macro definition?  Windows?

I think so, gmtime(..) is the common definition.

Thanks
Patrick

From: Florian Weimer <fweimer at redhat.com>
Sent: Wednesday, November 28, 2018 11:26 PM
To: Patrick Zhang
Cc: jdk-dev at openjdk.java.net
Subject: Re: OpenJDK fails to build with GCC when the #include<time.h> inside zip.cpp comes from a non-sysroot path
  

* Patrick Zhang:

> When I build on the latest jdk/jdk code base with GCC 8.2 (configured
> sysroot as a customized path instead of default root directory of the
> linux system),

I doubt it has anything to do with a sysroot vs non-sysroot
configuration.

> it failed with error:
> "jdk.pack/share/native/common-unpack/zip.cpp:420:23: error:
> declaration of 'tm* gmtime_r(const time_t*, tm*)' has a different
> exception specifier".

The declaration of gmtime_r should be removed.  Apparently, the comment
in the OpenJDK is wrong and the declaration is included even on
non-Solaris systems.

With glibc, you can declare your own gmtime_r function this way, but not
if you include the <time.h> header.  GCC 9 will also warn if we add
additional attributes (e.g. for nonnull warnings), so replicating the
declaration from <time.h> is a losing battle.

Which system needs the gmtime_r macro definition?  Windows?

Thanks,
Florian