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, 1 insertions, 20 deletions

diff --git a/src/libstd/build.rs b/src/libstd/build.rs
index c32bca82bd5..e879d440643 100644
--- a/src/libstd/build.rs
+++ b/src/libstd/build.rs
@@ -28,9 +28,7 @@ fn main() {
     }
 
     if target.contains("linux") {
-        if target.contains("musl") && (target.contains("x86_64") || target.contains("i686")) {
-            println!("cargo:rustc-link-lib=static=unwind");
-        } else if target.contains("android") {
+        if target.contains("android") {
             println!("cargo:rustc-link-lib=dl");
             println!("cargo:rustc-link-lib=log");
             println!("cargo:rustc-link-lib=gcc");
@@ -38,27 +36,13 @@ fn main() {
             println!("cargo:rustc-link-lib=dl");
             println!("cargo:rustc-link-lib=rt");
             println!("cargo:rustc-link-lib=pthread");
-            println!("cargo:rustc-link-lib=gcc_s");
         }
     } else if target.contains("freebsd") {
         println!("cargo:rustc-link-lib=execinfo");
         println!("cargo:rustc-link-lib=pthread");
-        println!("cargo:rustc-link-lib=gcc_s");
     } else if target.contains("dragonfly") || target.contains("bitrig") ||
               target.contains("netbsd") || target.contains("openbsd") {
         println!("cargo:rustc-link-lib=pthread");
-
-        if target.contains("rumprun") {
-            println!("cargo:rustc-link-lib=unwind");
-        } else if target.contains("netbsd") {
-            println!("cargo:rustc-link-lib=gcc_s");
-        } else if target.contains("openbsd") {
-            println!("cargo:rustc-link-lib=gcc");
-        } else if target.contains("bitrig") {
-            println!("cargo:rustc-link-lib=c++abi");
-        } else if target.contains("dragonfly") {
-            println!("cargo:rustc-link-lib=gcc_pic");
-        }
     } else if target.contains("apple-darwin") {
         println!("cargo:rustc-link-lib=System");
     } else if target.contains("apple-ios") {
@@ -67,9 +51,6 @@ fn main() {
         println!("cargo:rustc-link-lib=framework=Security");
         println!("cargo:rustc-link-lib=framework=Foundation");
     } else if target.contains("windows") {
-        if target.contains("windows-gnu") {
-            println!("cargo:rustc-link-lib=gcc_eh");
-        }
         println!("cargo:rustc-link-lib=advapi32");
         println!("cargo:rustc-link-lib=ws2_32");
         println!("cargo:rustc-link-lib=userenv");