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, 123 deletions

diff --git a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
index 8d880917166..5f7ad6918cd 100644
--- a/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
+++ b/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs
@@ -15,6 +15,7 @@ use mem;
 use sync::StaticMutex;
 
 use super::super::printing::print;
+use unwind as uw;
 
 #[inline(never)] // if we know this is a function call, we can skip it when
                  // tracing
@@ -102,126 +103,3 @@ pub fn write(w: &mut Write) -> io::Result<()> {
         uw::_URC_NO_REASON
     }
 }
-
-/// Unwind library interface used for backtraces
-///
-/// Note that dead code is allowed as here are just bindings
-/// iOS doesn't use all of them it but adding more
-/// platform-specific configs pollutes the code too much
-#[allow(non_camel_case_types)]
-#[allow(non_snake_case)]
-mod uw {
-    pub use self::_Unwind_Reason_Code::*;
-
-    use libc;
-
-    #[repr(C)]
-    pub enum _Unwind_Reason_Code {
-        _URC_NO_REASON = 0,
-        _URC_FOREIGN_EXCEPTION_CAUGHT = 1,
-        _URC_FATAL_PHASE2_ERROR = 2,
-        _URC_FATAL_PHASE1_ERROR = 3,
-        _URC_NORMAL_STOP = 4,
-        _URC_END_OF_STACK = 5,
-        _URC_HANDLER_FOUND = 6,
-        _URC_INSTALL_CONTEXT = 7,
-        _URC_CONTINUE_UNWIND = 8,
-        _URC_FAILURE = 9, // used only by ARM EABI
-    }
-
-    pub enum _Unwind_Context {}
-
-    pub type _Unwind_Trace_Fn =
-            extern fn(ctx: *mut _Unwind_Context,
-                      arg: *mut libc::c_void) -> _Unwind_Reason_Code;
-
-    extern {
-        // No native _Unwind_Backtrace on iOS
-        #[cfg(not(all(target_os = "ios", target_arch = "arm")))]
-        pub fn _Unwind_Backtrace(trace: _Unwind_Trace_Fn,
-                                 trace_argument: *mut libc::c_void)
-                    -> _Unwind_Reason_Code;
-
-        // available since GCC 4.2.0, should be fine for our purpose
-        #[cfg(all(not(all(target_os = "android", target_arch = "arm")),
-                  not(all(target_os = "linux", target_arch = "arm"))))]
-        pub fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
-                                 ip_before_insn: *mut libc::c_int)
-                    -> libc::uintptr_t;
-
-        #[cfg(all(not(target_os = "android"),
-                  not(all(target_os = "linux", target_arch = "arm"))))]
-        pub fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
-            -> *mut libc::c_void;
-    }
-
-    // On android, the function _Unwind_GetIP is a macro, and this is the
-    // expansion of the macro. This is all copy/pasted directly from the
-    // header file with the definition of _Unwind_GetIP.
-    #[cfg(any(all(target_os = "android", target_arch = "arm"),
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_GetIP(ctx: *mut _Unwind_Context) -> libc::uintptr_t {
-        #[repr(C)]
-        enum _Unwind_VRS_Result {
-            _UVRSR_OK = 0,
-            _UVRSR_NOT_IMPLEMENTED = 1,
-            _UVRSR_FAILED = 2,
-        }
-        #[repr(C)]
-        enum _Unwind_VRS_RegClass {
-            _UVRSC_CORE = 0,
-            _UVRSC_VFP = 1,
-            _UVRSC_FPA = 2,
-            _UVRSC_WMMXD = 3,
-            _UVRSC_WMMXC = 4,
-        }
-        #[repr(C)]
-        enum _Unwind_VRS_DataRepresentation {
-            _UVRSD_UINT32 = 0,
-            _UVRSD_VFPX = 1,
-            _UVRSD_FPAX = 2,
-            _UVRSD_UINT64 = 3,
-            _UVRSD_FLOAT = 4,
-            _UVRSD_DOUBLE = 5,
-        }
-
-        type _Unwind_Word = libc::c_uint;
-        extern {
-            fn _Unwind_VRS_Get(ctx: *mut _Unwind_Context,
-                               klass: _Unwind_VRS_RegClass,
-                               word: _Unwind_Word,
-                               repr: _Unwind_VRS_DataRepresentation,
-                               data: *mut libc::c_void)
-                -> _Unwind_VRS_Result;
-        }
-
-        let mut val: _Unwind_Word = 0;
-        let ptr = &mut val as *mut _Unwind_Word;
-        let _ = _Unwind_VRS_Get(ctx, _Unwind_VRS_RegClass::_UVRSC_CORE, 15,
-                                _Unwind_VRS_DataRepresentation::_UVRSD_UINT32,
-                                ptr as *mut libc::c_void);
-        (val & !1) as libc::uintptr_t
-    }
-
-    // This function doesn't exist on Android or ARM/Linux, so make it same
-    // to _Unwind_GetIP
-    #[cfg(any(all(target_os = "android", target_arch = "arm"),
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_GetIPInfo(ctx: *mut _Unwind_Context,
-                                    ip_before_insn: *mut libc::c_int)
-        -> libc::uintptr_t
-    {
-        *ip_before_insn = 0;
-        _Unwind_GetIP(ctx)
-    }
-
-    // This function also doesn't exist on Android or ARM/Linux, so make it
-    // a no-op
-    #[cfg(any(target_os = "android",
-              all(target_os = "linux", target_arch = "arm")))]
-    pub unsafe fn _Unwind_FindEnclosingFunction(pc: *mut libc::c_void)
-        -> *mut libc::c_void
-    {
-        pc
-    }
-}