8256012: Fix build of Monocle for Linux

[jgneff]

This pull request fixes the error when building embedded JavaFX for Linux.

The error occurs because MonocleGLFactory.c does not define the macro __USE_GNU before including the header file dlfcn.h. The two lines in the conditional group "#ifndef ANDROID" below have no effect because the header file has already been included at that point, and the header contains include guards to ignore subsequent attempts.

MonocleGLFactory.c

...
#include <EGL/egl.h>
#include "eglUtils.h"

#include "../PrismES2Defs.h"

#include "com_sun_prism_es2_MonocleGLContext.h"
#ifndef ANDROID
#define __USE_GNU
#include <dlfcn.h>
#endif
...

The -H option of gcc prints the name of each header file used. Its output shows that egl.h ends up including dlfcn.h indirectly, but without the required macro definition.

$ grep -e 'EGL/egl.h' -e 'eglUtils.h' -e 'dlfcn.h' headers.log
. opt/vc/include/EGL/egl.h
...... usr/include/dlfcn.h
....... usr/include/arm-linux-gnueabihf/bits/dlfcn.h
. monocle/eglUtils.h

For the proposed fix, I referred to the page of the Linux Programmer's Manual at "man dlsym" which states, "The _GNU_SOURCE feature test macro must be defined in order to obtain the definitions of RTLD_DEFAULT and RTLD_NEXT from <dlfcn.h>." I also used information in the following two Stack Overflow conversations:

• 'RTLD_NEXT' undeclared
• _GNU_SOURCE and __USE_GNU

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issue

• JDK-8256012: Fix build of Monocle for Linux

Reviewers

• Johan Vos (@johanvos - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jfx pull/350/head:pull/350
$ git checkout pull/350

[bridgekeeper]

👋 Welcome back jgneff! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[mlbridge]

Webrevs

• 02: Full - Incremental (2d044e7)
• 01: Full - Incremental (d3a8f0d)
• 00: Full (9ae6208)

[johanvos]

I don't see any harm in this PR, but I wonder which toolchains are still not having RTLD_NEXT without specifying GNU_SOURCE. Does it also work if you specify -D__USE_GNU to the compiler?

[jgneff]

I don't see any harm in this PR, but I wonder which toolchains are still not having RTLD_NEXT without specifying GNU_SOURCE.

Thanks, Johan. I've been following the instructions in the OpenJFX Wiki. I use the GCC cross-compiler installed by the repository's crosslibs-armv6hf.sh script. Then I build for ARM using the repository's armv6hf.gradle build file.

Does it also work if you specify -D__USE_GNU to the compiler?

No, that prints the same error. The comments in the header file /usr/include/features.h suggest that the macro __USE_GNU is for internal use, while _GNU_SOURCE is defined by the user. I tried the user macro, and it works!

So below is an alternative fix in the ARM build file:

diff --git a/buildSrc/armv6hf.gradle b/buildSrc/armv6hf.gradle
index 05e3e83551..bd56dcf86c 100644
--- a/buildSrc/armv6hf.gradle
+++ b/buildSrc/armv6hf.gradle
@@ -140,7 +140,7 @@ def iioCFlags = [extraCFlags,
          ].flatten()
 def iioLFlags = [extraLFlags].flatten()

-def es2EglfbCFlags = [extraCFlags, "-DIS_EGLFB", "-DLINUX"].flatten()
+def es2EglfbCFlags = [extraCFlags, "-DIS_EGLFB", "-DLINUX", "-D_GNU_SOURCE"].flatten()
 def es2EglfbLFlags = [extraLFlags].flatten()
 def es2MonocleCFlags = [extraCFlags, "-DIS_EGLFB", "-DLINUX"].flatten()
 def es2MonocleLFlags = [extraLFlags].flatten()

It seems the _GNU_SOURCE macro does a lot, so it's a question of limiting its use to one C file or enabling it for the entire prism_es2_monocle library. I'm fine with either solution.

[johanvos]

I think it is safer to use it as a flag for all monocle-es2 compilation then. It is also less intrusive as it doesn't require code changes, so it only affects specific builds.

[openjdk]

@jgneff This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8256012: Fix build of Monocle for Linux

Reviewed-by: jvos

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

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[johanvos]

@jgneff this looks good to be merged now. You can integrate it and then I will sponsor this.

[jgneff]

/integrate

[openjdk]

@jgneff
Your change (at version 2d044e7) is now ready to be sponsored by a Committer.

[johanvos]

/sponsor

[openjdk]

@johanvos @jgneff Pushed as commit 97d655f.

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