SGX target: simplify usercall internals

[jethrogb]

This moves logic from assembly to Rust and removes the special case for exit/panic handling, merging it with regular usercall handling.

Also, this fixes a bug in the exit usercall introduced in a75ae00. The bug would make regular exits look like panics with high probability. It would also with some probability leak information through uncleared registers.

cc @VardhanThigle

r? @alexcrichton

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:102dd250:start=1549472906374749143,finish=1549473004216121198,duration=97841372055
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---

[00:07:28] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:26: line longer than 100 chars
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:173: line longer than 100 chars
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:189: line longer than 100 chars
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:205: line longer than 100 chars
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:220: line longer than 100 chars
[00:07:28] tidy error: /checkout/src/libstd/sys/sgx/abi/usercalls/raw.rs:234: line longer than 100 chars
[00:07:29] some tidy checks failed
[00:07:29] 
[00:07:29] 
[00:07:29] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:07:29] 
[00:07:29] 
[00:07:29] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:07:29] Build completed unsuccessfully in 0:00:46
[00:07:29] Build completed unsuccessfully in 0:00:46
[00:07:29] make: *** [tidy] Error 1
[00:07:29] Makefile:68: recipe for target 'tidy' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:00473384
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Wed Feb  6 17:17:52 UTC 2019
---
travis_time:end:0e88b464:start=1549473473520725912,finish=1549473473525365568,duration=4639656
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:03d2cafd
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:0566f070
travis_time:start:0566f070
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:3b874afc
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[alexcrichton]

@bors: r+

[bors]

📌 Commit 0d2ab0b has been approved by alexcrichton

[Centril]

Adding space for rollup, @bors p=1

[bors]

⌛ Testing commit 0d2ab0b with merge f3fb1b1cdf9f57cebe750ba597732beabc7b64c6...

[bors]

💔 Test failed - checks-travis

[rust-highfive]

The job arm-android of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[01:42:06] test string::test_str_clear ... ok
[01:42:06] test string::test_str_truncate_invalid_len ... ok
[01:42:06] test string::test_str_truncate ... ok
[01:42:06] test string::test_str_truncate_split_codepoint ... ok
[01:42:06] died due to signal 11
[01:42:06] 
[01:42:06] 
[01:42:06] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "arm-linux-androideabi" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "alloc" "--"
[01:42:06] expected success, got: exit code: 3
---
travis_time:end:09637c74:start=1550034732702458711,finish=1550034732712632745,duration=10174034
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:277fc860
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:027cd0d8
travis_time:start:027cd0d8
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:0f5c2305
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[jethrogb]

Looks like #55861

[kennytm]

@bors retry

[bors]

⌛ Testing commit 0d2ab0b with merge ccd23b9...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: alexcrichton
Pushing ccd23b9 to master...