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Whilst this isn't really in production. I was porting AOSP to an Android TV I owned. However, I wanted to use the latest version of Android, but I had some clos

Whilst this isn't really in production. I was porting AOSP to an Android TV I owned. However, I wanted to use the latest version of Android, but I had some closed-source graphics composition binary blobs to interface with; they were for an older Android API. Naturally, this meant writing a wrapper from the new API back to the old API. For some reason, every so often (sporadically) I'd get a segfault inside the closed-source binary blob. To get things "working", in my wrapper, I captured the stack before calling the occasionally segfaulting function, and setup a segfault handler that would simply restore the stack to its state prior to the crash. Unfortunately, after restoring the stack, a subsequent call to the closed-source function would hang. I did some preliminary reverse engineering of the binary blobs and found that it was segfaulting whilst having retained a mutex. So I did, ah... the obvious thing(?) and just grabbed the raw memory address of the mutex, and released it myself when a segfault was encountered. Surprisingly this all "worked". In the end I had a TV that thought it was a 65" phone, lock screen and all. Umm, yay! Here's the code: https://gist.github.com/Benjamin-Dobell/bb13f6169aaa486254537c5e973e53ec https://gist.github.com/Benjamin-Dobell/bb13f6169aaa48625453...

gandreani 9y ago
Wow. Thanks for sharing your story. The way you casually explained this to me really threw me off. I remember trying to do some AOSP hacking on some older phones and always gave up. For different reasons Locked Bootloaders Huge sources to download Confusing device configuration (all those xml files were and still are magic to me) The farthest I ever got was to compile a kernel and flash it unto a phone. I was so happy for so little. The only difference was the change to the build version / name. I remember back in the pre Ice cream era graphics drivers were the most often quoted reason for older devices getting "stuck" on older versions of Android. It never occurred to me that you can write a graphics wrapper.

gandreani 9y ago

Wow. Thanks for sharing your story. The way you casually explained this to me really threw me off. I remember trying to do some AOSP hacking on some older phones and always gave up. For different reasons Locked Bootloaders Huge sources to download Confusing device configuration (all those xml files were and still are magic to me) The farthest I ever got was to compile a kernel and flash it unto a phone. I was so happy for so little. The only difference was the change to the build version / name. I remember back in the pre Ice cream era graphics drivers were the most often quoted reason for older devices getting "stuck" on older versions of Android. It never occurred to me that you can write a graphics wrapper.