check target abi support

[TimNN]

This PR checks for each extern function / block whether the ABI / calling convention used is supported by the current target.

This was achieved by adding an abi_blacklist field to the target specifications, listing the calling conventions unsupported for that target.

[rust-highfive]

r? @pnkfelix

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[TimNN]

cc @alexcrichton - I think you are one of the "experts" of the target related stuff.

[alexcrichton]

Thanks for the PR! Is there an associated issue with this as well? I'd naively expect that all ABIs are supported everywhere (e.g. they're just register definitions), but I'm likely missing something...

[TimNN]

There are multiple (related) issues: #36142, #36348, #24958

Summary: LLVM can assert (or apparently even segfault) when encountering unsupported calling conventions.

[alexcrichton]

Ok, sounds good to me! The strategy here looks good to me as well in that case.

We want to be sure to not regress anything as well (unfortunately crater won't be much help here), but perhaps this example could be used to figure out which calling conventions are allowed on which platforms?

[TimNN]

Alright so I did a bit of testing:

Test sources and script are here: https://gist.github.com/0582b8a1f9a1f35cbf06a8a144b82bf2

The results on OS X with nightly-2016-09-15 are also here: https://docs.google.com/spreadsheets/d/1LImcJbNuLOEjfzxsCOI1dYzwkpp7guLAQTb48jq1YLY/edit

Summary:

• arm only supports cdecl and aapcs
• vectorcall llvm asserts on i586 windows targets (in getFPReg)
• win64 and sysv64 llvm assert on i368-apple-ios and i686-apple-darwin (in getLLVMRegNum)
• asmjs and nacl fail with "no vaialable targets are compatible with this triple" (probably expected)
• mips64 targets ICE with data layout mismatch (with LLVM default)
• powerpc64-unknown-linux-gnu ICEs (even for the reference "C" abi) with 'assertion failed:(left == right)(left:Indirect, right:Direct)', ../src/librustc_trans/abi.rs:100

Conclusions:

• Allow only cdecl and aapcs on ARM
• The mips64 stuff should probably be fixed by just updating our datalayout?
• The powerpc64-unknown-linux-gnu should probably be fixed as well
• No idea about asmjs or nacl
• No idea about the other "llvm assert"s, these are probably upstream bugs?

[alexcrichton]

Awesome, thanks for the investigation! That all looks great to me. We basically just don't want to break anyone, so whether it's an assert or a legit error it should be fine to ignore. Want to use that as a whitelist for figuring out which platforms can use which ABI?

[bors]

☔ The latest upstream changes (presumably #36818) made this pull request unmergeable. Please resolve the merge conflicts.

[TimNN]

So I (finally!) updated this PR with the following changes:

• Instead of a whitelist we now have a blacklist
• The blacklist entries are currently the arm ones:
  • For the other failures I don't know if they are potential bugs in rustc / llvm or really unsupported calling conventions.
• The spreadsheet at https://docs.google.com/spreadsheets/d/1LImcJbNuLOEjfzxsCOI1dYzwkpp7guLAQTb48jq1YLY/edit has been updated with the latest nightly on macOS and Linux

[alexcrichton]

@bors: r+

Awesome, thanks @TimNN!

[bors]

📌 Commit 9eb0fd9 has been approved by alexcrichton

[bors]

⌛ Testing commit 9eb0fd9 with merge f542ad1...

[bors]

💔 Test failed - auto-linux-64-x-android-t

[TimNN]

I updated the tests, hope I've got them all.

But just to check, // ignore-arm ignores armv7 stuff as well, does it (in compiletest)?

[alexcrichton]

@bors: r+

[bors]

📌 Commit 1422ac9 has been approved by alexcrichton

[bors]

⌛ Testing commit 1422ac9 with merge 586a988...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-cargotest, auto-linux-64-cross-freebsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-rustbuild
Approved by: alexcrichton
Pushing 586a988 to master...