rustc: Implement custom panic runtimes

This commit is an implementation of [RFC 1513] which allows applications to
alter the behavior of panics at compile time. A new compiler flag, `-C panic`,
is added and accepts the values `unwind` or `panic`, with the default being
`unwind`. This model affects how code is generated for the local crate, skipping
generation of landing pads with `-C panic=abort`.

[RFC 1513]: https://github.com/rust-lang/rfcs/blob/master/text/1513-less-unwinding.md

Panic implementations are then provided by crates tagged with
`#![panic_runtime]` and lazily required by crates with
`#![needs_panic_runtime]`. The panic strategy (`-C panic` value) of the panic
runtime must match the final product, and if the panic strategy is not `abort`
then the entire DAG must have the same panic strategy.

With the `-C panic=abort` strategy, users can expect a stable method to disable
generation of landing pads, improving optimization in niche scenarios,
decreasing compile time, and decreasing output binary size. With the `-C
panic=unwind` strategy users can expect the existing ability to isolate failure
in Rust code from the outside world.

Organizationally, this commit dismantles the `sys_common::unwind` module in
favor of some bits moving part of it to `libpanic_unwind` and the rest into the
`panicking` module in libstd. The custom panic runtime support is pretty similar
to the custom allocator support with the only major difference being how the
panic runtime is injected (takes the `-C panic` flag into account).

1 files changed, 29 insertions, 23 deletions

diff --git a/src/rustc/std_shim/Cargo.lock b/src/rustc/std_shim/Cargo.lock
index 530c04da8a0..bad46966ffa 100644
--- a/src/rustc/std_shim/Cargo.lock
+++ b/src/rustc/std_shim/Cargo.lock
@@ -6,15 +6,6 @@ dependencies = [
 ]
 
 [[package]]
-name = "advapi32-sys"
-version = "0.1.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-dependencies = [
- "winapi 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "winapi-build 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
-]
-
-[[package]]
 name = "alloc"
 version = "0.0.0"
 dependencies = [
@@ -27,7 +18,7 @@ version = "0.0.0"
 dependencies = [
  "build_helper 0.1.0",
  "core 0.0.0",
- "gcc 0.3.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "gcc 0.3.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.0.0",
 ]
 
@@ -58,18 +49,32 @@ version = "0.0.0"
 
 [[package]]
 name = "gcc"
-version = "0.3.17"
+version = "0.3.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
+name = "libc"
+version = "0.0.0"
 dependencies = [
- "advapi32-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "winapi 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "core 0.0.0",
 ]
 
 [[package]]
-name = "libc"
+name = "panic_abort"
 version = "0.0.0"
 dependencies = [
  "core 0.0.0",
+ "libc 0.0.0",
+]
+
+[[package]]
+name = "panic_unwind"
+version = "0.0.0"
+dependencies = [
+ "alloc 0.0.0",
+ "core 0.0.0",
+ "libc 0.0.0",
+ "unwind 0.0.0",
 ]
 
 [[package]]
@@ -96,19 +101,20 @@ dependencies = [
  "build_helper 0.1.0",
  "collections 0.0.0",
  "core 0.0.0",
- "gcc 0.3.17 (registry+https://github.com/rust-lang/crates.io-index)",
+ "gcc 0.3.26 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.0.0",
+ "panic_abort 0.0.0",
+ "panic_unwind 0.0.0",
  "rand 0.0.0",
  "rustc_unicode 0.0.0",
+ "unwind 0.0.0",
 ]
 
 [[package]]
-name = "winapi"
-version = "0.2.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-
-[[package]]
-name = "winapi-build"
-version = "0.1.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
+name = "unwind"
+version = "0.0.0"
+dependencies = [
+ "core 0.0.0",
+ "libc 0.0.0",
+]