mk: Add support for musl-based builds

This commit adds support to the makefiles, configuration script, and build
system to understand MUSL. This is broken up into a few parts:

* Any target of the form `*-musl` requires the `--musl-root` option to
  `./configure` which will indicate the root of the MUSL installation. It is
  also expected that there is a libunwind build inside of that installation
  built against that MUSL.

* Objects from MUSL are copied into the build tree for Rust to be statically
  linked into the appropriate Rust library.

* Objects for binary startup and shutdown are included in each Rust installation
  by default for MUSL. This requires MUSL to only be installed on the machine
  compiling rust. Only a linker will be necessary for compiling against MUSL on
  a target machine.

Eventually a MUSL and/or libunwind build may be integrated by default into the
build but for now they are just always assumed to exist externally.

configure

@@ -583,6 +583,7 @@ valopt jemalloc-root "" "set directory where libjemalloc_pic.a is located"
 valopt build "${DEFAULT_BUILD}" "GNUs ./configure syntax LLVM build triple"
 valopt android-cross-path "/opt/ndk_standalone" "Android NDK standalone path"
 valopt release-channel "dev" "the name of the release channel to build"
+valopt musl-root "/usr/local" "MUSL root installation directory"
 
 # Many of these are saved below during the "writing configuration" step
 # (others are conditionally saved).
@@ -1058,6 +1059,13 @@ do
             fi
             ;;
 
+
+        *-musl)
+            if [ ! -f $CFG_MUSL_ROOT/lib/libc.a ]
+            then
+                err "musl libc $CFG_MUSL_ROOT/lib/libc.a not found"
+            fi
+            ;;
         *)
             ;;
     esac

mk/cfg/x86_64-unknown-linux-musl.mk

@@ -0,0 +1,27 @@
+# x86_64-unknown-linux-musl configuration
+CC_x86_64-unknown-linux-musl=$(CFG_MUSL_ROOT)/bin/musl-gcc
+CXX_x86_64-unknown-linux-musl=notaprogram
+CPP_x86_64-unknown-linux-musl=$(CFG_MUSL_ROOT)/bin/musl-gcc -E
+AR_x86_64-unknown-linux-musl=$(AR)
+CFG_LIB_NAME_x86_64-unknown-linux-musl=lib$(1).so
+CFG_STATIC_LIB_NAME_x86_64-unknown-linux-musl=lib$(1).a
+CFG_LIB_GLOB_x86_64-unknown-linux-musl=lib$(1)-*.so
+CFG_JEMALLOC_CFLAGS_x86_64-unknown-linux-musl := -m64
+CFG_GCCISH_CFLAGS_x86_64-unknown-linux-musl := -Wall -Werror -g -fPIC -m64
+CFG_GCCISH_CXXFLAGS_x86_64-unknown-linux-musl :=
+CFG_GCCISH_LINK_FLAGS_x86_64-unknown-linux-musl :=
+CFG_GCCISH_DEF_FLAG_x86_64-unknown-linux-musl :=
+CFG_LLC_FLAGS_x86_64-unknown-linux-musl :=
+CFG_INSTALL_NAME_x86_64-unknown-linux-musl =
+CFG_EXE_SUFFIX_x86_64-unknown-linux-musl =
+CFG_WINDOWSY_x86_64-unknown-linux-musl :=
+CFG_UNIXY_x86_64-unknown-linux-musl := 1
+CFG_LDPATH_x86_64-unknown-linux-musl :=
+CFG_RUN_x86_64-unknown-linux-musl=$(2)
+CFG_RUN_TARG_x86_64-unknown-linux-musl=$(call CFG_RUN_x86_64-unknown-linux-musl,,$(2))
+CFG_GNU_TRIPLE_x86_64-unknown-linux-musl := x86_64-unknown-linux-musl
+
+NATIVE_DEPS_libc_T_x86_64-unknown-linux-musl += libc.a
+NATIVE_DEPS_std_T_x86_64-unknown-linux-musl += libunwind.a \
+	crt1.o crti.o crtn.o
+INSTALLED_OBJECTS_x86_64-unknown-linux-musl += crt1.o crti.o crtn.o

mk/crates.mk

@@ -123,6 +123,9 @@ ONLY_RLIB_rustc_bitflags := 1
 # Documented-by-default crates
 DOC_CRATES := std alloc collections core libc rustc_unicode
 
+# Installed objects/libraries by default
+INSTALLED_OBJECTS := libmorestack.a libcompiler-rt.a
+
 ################################################################################
 # You should not need to edit below this line
 ################################################################################

mk/main.mk

@@ -399,8 +399,10 @@ endif
 # Prerequisites for using the stageN compiler to build target artifacts
 TSREQ$(1)_T_$(2)_H_$(3) = \
 	$$(HSREQ$(1)_H_$(3)) \
-	$$(TLIB$(1)_T_$(2)_H_$(3))/libmorestack.a \
-	$$(TLIB$(1)_T_$(2)_H_$(3))/libcompiler-rt.a
+	$$(foreach obj,$$(INSTALLED_OBJECTS),\
+		$$(TLIB$(1)_T_$(2)_H_$(3))/$$(obj)) \
+	$$(foreach obj,$$(INSTALLED_OBJECTS_$(2)),\
+		$$(TLIB$(1)_T_$(2)_H_$(3))/$$(obj))
 
 # Prerequisites for a working stageN compiler and libraries, for a specific
 # target

mk/prepare.mk

@@ -140,8 +140,8 @@ prepare-target-$(2)-host-$(3)-$(1)-$(4): prepare-maybe-clean-$(4) \
           $$(if $$(findstring $(2),$$(CFG_HOST)), \
             $$(foreach crate,$$(HOST_CRATES), \
               $$(call PREPARE_LIB,$$(call CFG_LIB_GLOB_$(2),$$(crate)))),) \
-          $$(call PREPARE_LIB,libmorestack.a) \
-          $$(call PREPARE_LIB,libcompiler-rt.a),),),)
+	  $$(foreach object,$$(INSTALLED_OBJECTS) $$(INSTALLED_OBJECTS_$(2)),\
+	    $$(call PREPARE_LIB,$$(object))),),),)
 endef
 
 define INSTALL_GDB_DEBUGGER_SCRIPTS_COMMANDS

mk/rt.mk

@@ -74,7 +74,8 @@ $$(RT_OUTPUT_DIR_$(1))/%.o: $(S)src/rt/%.ll $$(MKFILE_DEPS) \
 	@mkdir -p $$(@D)
 	@$$(call E, compile: $$@)
 	$$(Q)$$(LLC_$$(CFG_BUILD)) $$(CFG_LLC_FLAGS_$(1)) \
-	    -filetype=obj -mtriple=$$(CFG_LLVM_TARGET_$(1)) -relocation-model=pic -o $$@ $$<
+	    -filetype=obj -mtriple=$$(CFG_LLVM_TARGET_$(1)) \
+	    -relocation-model=pic -o $$@ $$<
 
 $$(RT_OUTPUT_DIR_$(1))/%.o: $(S)src/rt/%.c $$(MKFILE_DEPS)
 	@mkdir -p $$(@D)
@@ -110,6 +111,11 @@ $$(RT_OUTPUT_DIR_$(1))/$$(NATIVE_$(2)_$(1)): $$(OBJS_$(2)_$(1))
 	@$$(call E, link: $$@)
 	$$(Q)$$(AR_$(1)) rcs $$@ $$^
 
+ifeq ($$(findstring windows,$(1)),windows)
+$$(RT_OUTPUT_DIR_$(1))/lib$(2).a: $$(RT_OUTPUT_DIR_$(1))/$$(NATIVE_$(2)_$(1))
+	$$(Q)cp $$< $$^
+endif
+
 endef
 
 $(foreach target,$(CFG_TARGET), \
@@ -312,6 +318,19 @@ endif # endif for windowsy
 endif # endif for ios
 endif # endif for darwin
 
+################################################################################
+# libc/libunwind for musl
+#
+# When we're building a musl-like target we're going to link libc/libunwind
+# statically into the standard library and liblibc, so we need to make sure
+# they're in a location that we can find
+################################################################################
+
+ifeq ($$(findstring musl,$(1)),musl)
+$$(RT_OUTPUT_DIR_$(1))/%: $$(CFG_MUSL_ROOT)/lib/%
+	cp $$^ $$@
+endif
+
 endef
 
 # Instantiate template for all stages/targets

mk/target.mk

@@ -35,7 +35,9 @@ CRATE_FULLDEPS_$(1)_T_$(2)_H_$(3)_$(4) := \
 		$$(foreach dep,$$(RUST_DEPS_$(4)), \
 		  $$(TLIB$(1)_T_$(2)_H_$(3))/stamp.$$(dep)) \
 		$$(foreach dep,$$(NATIVE_DEPS_$(4)), \
-		  $$(RT_OUTPUT_DIR_$(2))/$$(call CFG_STATIC_LIB_NAME_$(2),$$(dep)))
+		  $$(RT_OUTPUT_DIR_$(2))/$$(call CFG_STATIC_LIB_NAME_$(2),$$(dep))) \
+		$$(foreach dep,$$(NATIVE_DEPS_$(4)_T_$(2)), \
+		  $$(RT_OUTPUT_DIR_$(2))/$$(dep))
 endef
 
 $(foreach host,$(CFG_HOST), \
@@ -143,14 +145,7 @@ $$(TBIN$(1)_T_$(2)_H_$(3))/:
 $$(TLIB$(1)_T_$(2)_H_$(3))/:
 	mkdir -p $$@
 
-$$(TLIB$(1)_T_$(2)_H_$(3))/libcompiler-rt.a: \
-	    $$(RT_OUTPUT_DIR_$(2))/$$(call CFG_STATIC_LIB_NAME_$(2),compiler-rt) \
-	    | $$(TLIB$(1)_T_$(2)_H_$(3))/ $$(SNAPSHOT_RUSTC_POST_CLEANUP)
-	@$$(call E, cp: $$@)
-	$$(Q)cp $$< $$@
-
-$$(TLIB$(1)_T_$(2)_H_$(3))/libmorestack.a: \
-	    $$(RT_OUTPUT_DIR_$(2))/$$(call CFG_STATIC_LIB_NAME_$(2),morestack) \
+$$(TLIB$(1)_T_$(2)_H_$(3))/%: $$(RT_OUTPUT_DIR_$(2))/% \
 	    | $$(TLIB$(1)_T_$(2)_H_$(3))/ $$(SNAPSHOT_RUSTC_POST_CLEANUP)
 	@$$(call E, cp: $$@)
 	$$(Q)cp $$< $$@