Auto merge of #32900 - alexcrichton:panic2abort, r=nikomatsakis

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).

Closes #32837

Author: bors

mk/crates.mk

@@ -53,7 +53,8 @@ TARGET_CRATES := libc std term \
                  getopts collections test rand \
                  core alloc \
                  rustc_unicode rustc_bitflags \
-		 alloc_system alloc_jemalloc
+		 alloc_system alloc_jemalloc \
+		 panic_abort panic_unwind unwind
 RUSTC_CRATES := rustc rustc_typeck rustc_mir rustc_borrowck rustc_resolve rustc_driver \
                 rustc_trans rustc_back rustc_llvm rustc_privacy rustc_lint \
                 rustc_data_structures rustc_platform_intrinsics \
@@ -72,10 +73,18 @@ DEPS_libc := core
 DEPS_rand := core
 DEPS_rustc_bitflags := core
 DEPS_rustc_unicode := core
+DEPS_panic_abort := libc alloc
+DEPS_panic_unwind := libc alloc unwind
+DEPS_unwind := libc
+
+# FIXME(stage0): change this to just `RUSTFLAGS_panic_abort := ...`
+RUSTFLAGS1_panic_abort := -C panic=abort
+RUSTFLAGS2_panic_abort := -C panic=abort
+RUSTFLAGS3_panic_abort := -C panic=abort
 
 DEPS_std := core libc rand alloc collections rustc_unicode \
 	native:backtrace \
-	alloc_system
+	alloc_system panic_abort panic_unwind unwind
 DEPS_arena := std
 DEPS_glob := std
 DEPS_flate := std native:miniz
@@ -148,6 +157,9 @@ ONLY_RLIB_rustc_unicode := 1
 ONLY_RLIB_rustc_bitflags := 1
 ONLY_RLIB_alloc_system := 1
 ONLY_RLIB_alloc_jemalloc := 1
+ONLY_RLIB_panic_unwind := 1
+ONLY_RLIB_panic_abort := 1
+ONLY_RLIB_unwind := 1
 
 TARGET_SPECIFIC_alloc_jemalloc := 1
 

mk/tests.mk

@@ -23,7 +23,8 @@ DEPS_collectionstest :=
 $(eval $(call RUST_CRATE,collectionstest))
 
 TEST_TARGET_CRATES = $(filter-out core rustc_unicode alloc_system libc \
-		     		  alloc_jemalloc,$(TARGET_CRATES)) \
+		     		  alloc_jemalloc panic_unwind \
+				  panic_abort,$(TARGET_CRATES)) \
 			collectionstest coretest
 TEST_DOC_CRATES = $(DOC_CRATES) arena flate fmt_macros getopts graphviz \
                 log rand rbml serialize syntax term test