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Can you post the error log?

The first error is : 

E/AndroidRuntime(24105): java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "signal" referenced by "libSDL2.so"...

-> If, I comment HAVE_SIGNAL, HAVE_SIGACTION

I have : 

E/AndroidRuntime(25255): java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "atof" referenced by "libSDL2.so"...

-> If, I comment HAVE_ATOF:

E/AndroidRuntime(25671): java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "sigemptyset" referenced by "libSDL2.so"...

... Then : 

E/AndroidRuntime(29050): java.lang.UnsatisfiedLinkError: dlopen failed: cannot locate symbol "srand" referenced by "libSDL2.so"...


Adding libc, libm does not solve the problem.
*Downgrading* to API-level 20 does solve the problem

I tried reproducing with the latest NDK for Linux, using androidbuild.sh and testgles2.c, the issue does not show up with the default project settings.

Let me know if you find out what's going on.

In case, it helps, here's some precision :

- api level 21
- ndk-r10c
- Linux 64-bit (x86)
- arch = arm-v7a

I will try later with testgles2

I can get the same problem with testgles2. I start with
../build-scripts/androidbuild.sh com.blabla.blabla testgles2.c 

I go to the build dir.
This build an .apk with the "dlopen" issue.

 ndk-build clean
 android update project  --target android-21 --path `pwd`
 ndk-build -j
 ant debug install


This build a correct .apk

 ndk-build clean
 android update project  --target android-20 --path `pwd`
 ndk-build -j
 ant debug install

Update.

This issue still exists with the NDK-r10d. 
When using API 21 and running on an old device (android < 5.0 ?) some function are missing.

functions are (at least) : signal, sigemptyset, atof, stpcpy (strcat and strcpy), srand, rand.


Very few modifications on SDL to get this working :

on SDL
======

Undefine android configuration :

HAVE_SIGNAL
HAVE_SIGACTION
HAVE_ATOF

In "SDL_systrhead.c", comment out the few block of lines with "sigemptyset".

Android.mk:
remove the compilation of "test" directory because it contains a few rand/srand calls

SDL_image / png
===============

There are 4 calls to "atof(param)" in "pngget.c" that can get replaced by "strtod(param,NULL)".



Also, there are more discussions about this in internet : 
https://groups.google.com/forum/#!topic/android-ndk/RjO9WmG9pfE
http://stackoverflow.com/questions/25475055/android-ndk-load-library-cannot-locate-srand

Can you provide a tested patch for this issue?

Thanks!

Created attachment 2182 [details]
patch

Patch for SDL_image

Created attachment 2183 [details]
patch

Patch for SDL

Created attachment 2184 [details]
patch for SDL / tests

Also a patch for SDL test.

replacing srand() by srand48()
replacing rand() by lrand48()

maybe otherfunction are to be replaced.

This is partially fixed with these commits:
https://hg.libsdl.org/SDL/rev/f2d87d87509f
https://hg.libsdl.org/SDL_image/rev/6292ebae060a

The rand/srand issue needs more work, and we probably need to add a config.h define for this.

Ok Thanks!

Anyway a quick workaround for "rand/srand" is to remove the compilation of "src/test/*.c" from "SDL/Android.mk".

After a long time, I found out more clearly what was going wrong.

The native libraries should be built with a "APP_PLATFORM" as low as possible.
Ideally, APP_PLATFORM should be equals to the minSdkVersion of the AndroidManifest.xml
So that the application never runs on a lower APP_PLATFORM than it has been built for.

An additional good patch would be to write explicitly in "jni/Application.mk": APP_PLATFORM=android-10

(If no APP_PLATFORM is set, the "targetSdkVersion" of the AndroidManifest.xml is applied as an APP_PLATFORM to the native libraries. And currently, this is bad, because targetSdkVersion is 12, whereas minSdkLevel is 10.
And in fact, there is a warning from ndk: "Android NDK: WARNING: APP_PLATFORM android-12 is larger than android:minSdkVersion 10 in ./AndroidManifest.xml".)


to precise what happened in the initial reported test-case:
Let say the "c" code contains a call to "srand()".

with APP_PLATFORM=android-21, libSDL2.so contains a undef reference to "srand()".
with APP_PLATFORM=android-10, libSDL2.so contains a undef reference to "srand48()".

but srand() is missing on devices with APP_PLATFORM=android-10 (it was in fact replaced by srand48()). 
So, if you build for android-21 (where srand() is available), you will really have a call to "srand()" and it will fail on android-10.
That was the issue. The path tried to fix this by in fact always calling srand48().


SDL patches that were applied are beneficial anyway, there are implicitly allowing they backward compatibility of using android-21 on a android-10 platform.
It can be helpful in case you want to target a higher APP_PLATFORM than minSdkVersion to have potentially access to more functions.
Eg you want to have access to GLES3 functions (or other) of "android-21". But, if dlopen() fails (on android-10), you do a fall-back to GLES2.

In fact, I would revert this commit:
https://hg.libsdl.org/SDL/rev/f2d87d87509f

because it has disabled some signals that commons to all platforms.

(And so, it's better to explicitly add "APP_PLATFORM=android-10" to jni/Application.mk)

Fixed, thanks!
https://hg.libsdl.org/SDL/rev/dde37ddd81bc