use PIE (full ASLR) by default on Android too

[thestinger]

Android no longer permits non-PIE executables.

Closes #17437

[alexcrichton]

We can't just instantly drop backtrace support on android, this needs to at least be investigate somewhat to see why backtraces are broken on android.

[thestinger]

@alexcrichton: Rust currently has no support for current Android versions at all because they only run executables built with PIE. Lacking support for the platform is worse than lacking symbol names in backtraces.

[thestinger]

The Android bot needs to be updated in order for this to have a chance of working. It isn't going to be possible to upgrade it without using PIE, because Android no longer allows non-PIE. Anyway, there's nothing I can do about that so I'll leave this here to rot.

[alexcrichton]

Let's please slow down a bit here.

• Have you verified by hand that backtrace-related tests do indeed work on an updated version of an android toolchain? (this is a concrete step forward)
• Do you have evidence to support your claim that it is impossible for backtraces to work with PIE?
• Precisely what versions of the toolchain and such do you think need to be updated?
• Do you know if this will break backwards compatibility?

[thestinger]

Do you have evidence to support your claim that it is impossible for backtraces to work with PIE?

When did I say this? They work fine with PIE on Linux.

Precisely what versions of the toolchain and such do you think need to be updated?

The NDK and Android version are out-of-date. Android has full support for PIE now and it became mandatory when there were no remaining problems. I know it's out-of-date because it's still working.

Do you know if this will break backwards compatibility?

It doesn't break compatibility.

[alexcrichton]

So the problem at hand is that enabling PIE breaks backtraces on android, do you know why that happens? It sounds like you're not willing to investigate, why I asked the questions.

[thestinger]

It works fine with -C link-args=-pie on my Android, but that uses CyanogenMod. It breaks PIE on the Android bot but I have no idea if it would still break if it was up-to-date.

[DanAlbert]

Building without PIE will still work fine for older versions of Android. The patch removing support for non-PIE isn't in any released version of Android yet.

There have recently been a lot of unwinder fixes in AOSP as well. Is it possible that the unwinder tests would be fixed by those?

[alexcrichton]

@thestinger, have you manually verified that this test passes on an updated android compiler/client? I've tested manually against what I believe is r9d and both the test and the bundled gdb itself fail to get symbols or backtrace correctly.

[emberian]

I think I accidentally did this in my branch, and I can confirm that the tests pass with r10c.

[alexcrichton]

Closing due to inactivity (and @bors's queue is quite full!). I also tested this on the r10c toolchain, like @cmr said, on the bots and it failed with the same error. I know @cmr and I chatted about this on IRC, but I forgot the outcome, @cmr do you remember?