std: Move pc-windows-gnu to SEH-based unwinding

This commit moves the `*-pc-windows-gnu` targets (e.g. the MinGW targets) to
use SEH-based unwinding instead of libunwind-based unwinding. There are a number
of ramifications on these targets as a result:

* Binary distributions of the standard library are no longer tied to a
  particular compiler toolchain. The MinGW toolchains typically ship with either
  SEH, Dwarf, or SjLj based unwinding and are binary-incompatible, but with SEH
  unwinding we'll be able to link with any of the toolchains.
* The GNU implementation is now much closer to the MSVC implementation, reducing
  the amount of duplicated code we'll have to maintain (yay!).
* Due to the loss of the libunwind stack unwinder the libbacktrace library is no
  longer used on Windows. The same unwinding code for MSVC is now used for GNU
  as well, and unfortunately this has empirically led to worse stack traces in
  the past. In theory, though, this should be fixed for both MSVC and GNU at the
  same time!
* Due to the lack of a need for frame unwind info registration, the `rsend.o`
  and `rsbegin.o` startup object files are no longer built. Additionally the
  `crt2.o` and `dllcrt2.o` files are no longer distributed. It's assumed that
  the linker in use will inject these as usual. The `-nostdlib` flag is no
  longer passed to the linker to indicate this.

This change also opened up the possibility to reorganize a few modules, so the
following changes were also made:

* The `custom_unwind_resume` option and all support code was removed from trans
  as this is no longer necessary.
* The `sys_common::unwind` module was refactored to have the platform-specific
  portions live in `sys::unwind`.
* A similar refactoring was applied to backtrace writing (just shuffling some
  files around).
* Documentation was updated in shuffled modules to reflect the current state of
  affairs.

Author: alexcrichton

mk/cfg/i686-pc-windows-gnu.mk

@@ -22,6 +22,5 @@ CFG_LDPATH_i686-pc-windows-gnu :=
 CFG_RUN_i686-pc-windows-gnu=$(2)
 CFG_RUN_TARG_i686-pc-windows-gnu=$(call CFG_RUN_i686-pc-windows-gnu,,$(2))
 CFG_GNU_TRIPLE_i686-pc-windows-gnu := i686-w64-mingw32
-CFG_THIRD_PARTY_OBJECTS_i686-pc-windows-gnu := crt2.o dllcrt2.o
-CFG_INSTALLED_OBJECTS_i686-pc-windows-gnu := crt2.o dllcrt2.o rsbegin.o rsend.o
-CFG_RUSTRT_HAS_STARTUP_OBJS_i686-pc-windows-gnu := 1
+CFG_THIRD_PARTY_OBJECTS_i686-pc-windows-gnu :=
+CFG_INSTALLED_OBJECTS_i686-pc-windows-gnu :=

mk/cfg/x86_64-pc-windows-gnu.mk

@@ -22,6 +22,5 @@ CFG_LDPATH_x86_64-pc-windows-gnu :=
 CFG_RUN_x86_64-pc-windows-gnu=$(2)
 CFG_RUN_TARG_x86_64-pc-windows-gnu=$(call CFG_RUN_x86_64-pc-windows-gnu,,$(2))
 CFG_GNU_TRIPLE_x86_64-pc-windows-gnu := x86_64-w64-mingw32
-CFG_THIRD_PARTY_OBJECTS_x86_64-pc-windows-gnu := crt2.o dllcrt2.o
-CFG_INSTALLED_OBJECTS_x86_64-pc-windows-gnu := crt2.o dllcrt2.o rsbegin.o rsend.o
-CFG_RUSTRT_HAS_STARTUP_OBJS_x86_64-pc-windows-gnu := 1
+CFG_THIRD_PARTY_OBJECTS_x86_64-pc-windows-gnu :=
+CFG_INSTALLED_OBJECTS_x86_64-pc-windows-gnu :=

mk/dist.mk

@@ -58,7 +58,6 @@ PKG_FILES := \
       libcoretest                              \
       libbacktrace                             \
       rt                                       \
-      rtstartup                                \
       rustllvm                                 \
       snapshots.txt                            \
       rust-installer                           \

mk/rt.mk

@@ -291,10 +291,8 @@ BACKTRACE_NAME_$(1) := $$(call CFG_STATIC_LIB_NAME_$(1),backtrace)
 BACKTRACE_LIB_$(1) := $$(RT_OUTPUT_DIR_$(1))/$$(BACKTRACE_NAME_$(1))
 BACKTRACE_BUILD_DIR_$(1) := $$(RT_OUTPUT_DIR_$(1))/libbacktrace
 
-# We don't use this on platforms that aren't linux-based (with the exception of
-# msys2/mingw builds on windows, which use it to read the dwarf debug
-# information) so just make the file available, the compilation of libstd won't
-# actually build it.
+# We don't use this on platforms that aren't linux-based so just make the file
+# available, the compilation of libstd won't actually build it.
 ifeq ($$(findstring darwin,$$(OSTYPE_$(1))),darwin)
 # See comment above
 $$(BACKTRACE_LIB_$(1)):
@@ -307,7 +305,7 @@ $$(BACKTRACE_LIB_$(1)):
 	touch $$@
 else
 
-ifeq ($$(findstring msvc,$(1)),msvc)
+ifeq ($$(findstring windows,$(1)),windows)
 # See comment above
 $$(BACKTRACE_LIB_$(1)):
 	touch $$@
@@ -382,10 +380,6 @@ endif # endif for darwin
 ifeq ($$(findstring musl,$(1)),musl)
 $$(RT_OUTPUT_DIR_$(1))/%: $$(CFG_MUSL_ROOT)/lib/%
 	cp $$^ $$@
-else
-# Ask gcc where it is
-$$(RT_OUTPUT_DIR_$(1))/%:
-	cp $$(shell $$(CC_$(1)) -print-file-name=$$(@F)) $$@
 endif
 
 endef

mk/target.mk

@@ -126,34 +126,6 @@ $$(TBIN$(1)_T_$(2)_H_$(3))/$(4)$$(X_$(2)): \
 
 endef
 
-# Macro for building runtime startup/shutdown object files;
-# these are Rust's equivalent of crti.o, crtn.o
-#
-# $(1) - stage
-# $(2) - target triple
-# $(3) - host triple
-# $(4) - object basename
-define TARGET_RUSTRT_STARTUP_OBJ
-
-$$(TLIB$(1)_T_$(2)_H_$(3))/$(4).o: \
-		$(S)src/rtstartup/$(4).rs \
-		$$(TLIB$(1)_T_$(2)_H_$(3))/stamp.core \
-		$$(HSREQ$(1)_T_$(2)_H_$(3)) \
-		| $$(TBIN$(1)_T_$(2)_H_$(3))/
-	@$$(call E, rustc: $$@)
-	$$(STAGE$(1)_T_$(2)_H_$(3)) --emit=obj -o $$@ $$<
-
-ifeq ($$(CFG_RUSTRT_HAS_STARTUP_OBJS_$(2)), 1)
-# Add dependencies on Rust startup objects to all crates that depend on core.
-# This ensures that they are built after core (since they depend on it),
-# but before everything else (since they are needed for linking dylib crates).
-$$(foreach crate, $$(TARGET_CRATES), \
-	$$(if $$(findstring core,$$(DEPS_$$(crate))), \
-		$$(TLIB$(1)_T_$(2)_H_$(3))/stamp.$$(crate))) : $$(TLIB$(1)_T_$(2)_H_$(3))/$(4).o
-endif
-
-endef
-
 # Every recipe in RUST_TARGET_STAGE_N outputs to $$(TLIB$(1)_T_$(2)_H_$(3),
 # a directory that can be cleaned out during the middle of a run of
 # the get-snapshot.py script.  Therefore, every recipe needs to have
@@ -166,7 +138,10 @@ SNAPSHOT_RUSTC_POST_CLEANUP=$(HBIN0_H_$(CFG_BUILD))/rustc$(X_$(CFG_BUILD))
 
 define TARGET_HOST_RULES
 
-$$(TLIB$(1)_T_$(2)_H_$(3))/:
+$$(TLIB$(1)_T_$(2)_H_$(3))/: | $$(SNAPSHOT_RUSTC_POST_CLEANUP)
+	mkdir -p $$@
+
+$$(TBIN$(1)_T_$(2)_H_$(3))/: | $$(SNAPSHOT_RUSTC_POST_CLEANUP)
 	mkdir -p $$@
 
 $$(TLIB$(1)_T_$(2)_H_$(3))/%: $$(RT_OUTPUT_DIR_$(2))/% \
@@ -197,8 +172,33 @@ $(foreach host,$(CFG_HOST), \
    $(foreach tool,$(TOOLS), \
     $(eval $(call TARGET_TOOL,$(stage),$(target),$(host),$(tool)))))))
 
+# FIXME(stage0) - remove everything here after a snapshot
+#
+# The stage0 compiler requires the rsend.o, rsbegin.o, crt2.o, and dllcrt2.o
+# startup objects on the pc-windows-gnu targets, but that's no longer the case.
+# Hack in support to the makefiles to ensure that these objects all exist.
+#
+# Note that the rs*.o files can just be blank object files.
+define STARTUP_OBJS_COMPAT
+ifeq ($$(findstring pc-windows-gnu,$(2)),pc-windows-gnu)
+DUMMY_DEPS_$(2)_H_$(3) := \
+	$$(TLIB$(1)_T_$(2)_H_$(3))/stamp.core \
+	$$(HSREQ$(1)_T_$(2)_H_$(3))/stamp.core
+$$(TLIB$(1)_T_$(2)_H_$(3))/rsend.o $$(TLIB$(1)_T_$(2)_H_$(3))/rsbegin.o: \
+		$$(DUMMY_DEPS_$(2)_H_$(3) \
+		| $$(TLIB$(1)_T_$(2)_H_$(3))/ $$(SNAPSHOT_RUSTC_POST_CLEANUP)
+	$$(CC_$(2)) $$(CFG_GCCISH_CFLAGS_$(2)) -c -x c - -o $$@ < /dev/null
+$$(TLIB$(1)_T_$(2)_H_$(3))/dllcrt2.o $$(TLIB$(1)_T_$(2)_H_$(3))/crt2.o: \
+		$$(DUMMY_DEPS_$(2)_H_$(3) \
+		| $$(TLIB$(1)_T_$(2)_H_$(3))/ $$(SNAPSHOT_RUSTC_POST_CLEANUP)
+	cp $$(shell $$(CC_$(2)) -print-file-name=$$(@F)) $$@
+$$(TLIB$(1)_T_$(2)_H_$(3))/stamp.std: \
+	$$(TLIB$(1)_T_$(2)_H_$(3))/rsend.o \
+	$$(TLIB$(1)_T_$(2)_H_$(3))/rsbegin.o \
+	$$(TLIB$(1)_T_$(2)_H_$(3))/dllcrt2.o \
+	$$(TLIB$(1)_T_$(2)_H_$(3))/crt2.o
+endif
+endef
 $(foreach host,$(CFG_HOST), \
  $(foreach target,$(CFG_TARGET), \
-  $(foreach stage,$(STAGES), \
-   $(foreach obj,rsbegin rsend, \
-    $(eval $(call TARGET_RUSTRT_STARTUP_OBJ,$(stage),$(target),$(host),$(obj)))))))
+  $(eval $(call STARTUP_OBJS_COMPAT,0,$(target),$(host)))))

src/doc/book/custom-allocators.md

@@ -138,9 +138,6 @@ pub extern fn __rust_usable_size(size: usize, _align: usize) -> usize {
 # fn main() {}
 # #[lang = "panic_fmt"] fn panic_fmt() {}
 # #[lang = "eh_personality"] fn eh_personality() {}
-# #[lang = "eh_unwind_resume"] extern fn eh_unwind_resume() {}
-# #[no_mangle] pub extern fn rust_eh_register_frames () {}
-# #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
 ```
 
 After we compile this crate, it can be used as follows:

src/doc/book/lang-items.md

@@ -59,9 +59,6 @@ fn main(argc: isize, argv: *const *const u8) -> isize {
 
 #[lang = "eh_personality"] extern fn eh_personality() {}
 #[lang = "panic_fmt"] fn panic_fmt() -> ! { loop {} }
-# #[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
-# #[no_mangle] pub extern fn rust_eh_register_frames () {}
-# #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
 ```
 
 Note the use of `abort`: the `exchange_malloc` lang item is assumed to

src/doc/book/no-stdlib.md

@@ -39,9 +39,6 @@ fn start(_argc: isize, _argv: *const *const u8) -> isize {
 // provided by libstd.
 #[lang = "eh_personality"] extern fn eh_personality() {}
 #[lang = "panic_fmt"] fn panic_fmt() -> ! { loop {} }
-# #[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
-# #[no_mangle] pub extern fn rust_eh_register_frames () {}
-# #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
 # // fn main() {} tricked you, rustdoc!
 ```
 
@@ -66,9 +63,6 @@ pub extern fn main(argc: i32, argv: *const *const u8) -> i32 {
 
 #[lang = "eh_personality"] extern fn eh_personality() {}
 #[lang = "panic_fmt"] fn panic_fmt() -> ! { loop {} }
-# #[lang = "eh_unwind_resume"] extern fn rust_eh_unwind_resume() {}
-# #[no_mangle] pub extern fn rust_eh_register_frames () {}
-# #[no_mangle] pub extern fn rust_eh_unregister_frames () {}
 # // fn main() {} tricked you, rustdoc!
 ```
 

src/librustc/middle/lang_items.rs

@@ -340,7 +340,6 @@ lets_do_this! {
 
     EhPersonalityLangItem,           "eh_personality",          eh_personality;
     EhPersonalityCatchLangItem,      "eh_personality_catch",    eh_personality_catch;
-    EhUnwindResumeLangItem,          "eh_unwind_resume",        eh_unwind_resume;
     MSVCTryFilterLangItem,           "msvc_try_filter",         msvc_try_filter;
 
     OwnedBoxLangItem,                "owned_box",               owned_box;

src/librustc/middle/weak_lang_items.rs

@@ -43,10 +43,6 @@ pub fn check_crate(krate: &hir::Crate,
     if items.eh_personality().is_none() {
         items.missing.push(lang_items::EhPersonalityLangItem);
     }
-    if sess.target.target.options.custom_unwind_resume &
-       items.eh_unwind_resume().is_none() {
-        items.missing.push(lang_items::EhUnwindResumeLangItem);
-    }
 
     {
         let mut cx = Context { sess: sess, items: items };
@@ -123,5 +119,4 @@ impl<'a, 'v> Visitor<'v> for Context<'a> {
 weak_lang_items! {
     panic_fmt,          PanicFmtLangItem,           rust_begin_unwind;
     eh_personality,     EhPersonalityLangItem,      rust_eh_personality;
-    eh_unwind_resume,   EhUnwindResumeLangItem,     rust_eh_unwind_resume;
 }