non-native ARM support via qemu

mkimage and hasher can make use of qemu to run
non-native binaries while working on the chroots;
thanks kas@, manowar@ and sbolshakov@ for implementing
this functionality as well as providing nice examples
through mkimage-profiles-arm and mkimage-profile-armrootfs.

This required the architecture check to be added since baking
a tarball with "arm" as its specified arch and x86_64 inside
isn't particularly good thing to let slip through; however
the implementation is quite fragile, bugreports and patches
are seriously welcome.

NB: APTCONF evaluation order between lazy make and nimble shell
turned out to be quite a delicate issue in this particular case.

doc/arm.txt

@@ -0,0 +1,18 @@
+Для сборки с применением трансляции посредством QEMU
+выполните от имени root следующие команды:
+
+apt-get install qemu-user-binfmt_misc
+modprobe binfmt_misc
+echo ":arm:M::\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00:\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff:/.host/qemu-arm:" > /proc/sys/fs/binfmt_misc/register
+echo 32768 > /proc/sys/vm/mmap_min_addr
+
+Если файл /proc/sys/fs/binfmt_misc/register не существует,
+потребуется установить и загрузить иное ядро (например, std-def).
+
+Также нужен sources.list с указанием arm-репозитория
+и ссылающийся на него apt.conf (см. apt.conf.sample);
+например:
+
+--- sources.list.sisyphus.arm
+rpm http://ftp.altlinux.org/pub/distributions/ALTLinux/Sisyphus arm classic
+---

image.in/Makefile

@@ -48,6 +48,7 @@ COPY_TREE = ./files
 # outdir shouldn't be wiped clean before use
 CLEANUP_OUTDIR ?=
 
+GLOBAL_TARGET := $(ARCH)
 GLOBAL_HSH_APT_CONFIG := $(wildcard $(APTCONF))
 
 # the lib/build-*.mk comes from features.in/build-*/lib
@@ -88,4 +89,6 @@ debug:
 	@echo "TOPDIR=$(TOPDIR)"
 	@echo "IMAGEDIR=$(IMAGEDIR)"
 	@echo "ARCH=$(ARCH)"
+	@echo "GLOBAL_TARGET=$(GLOBAL_TARGET)"
 	@echo "GLOBAL_HSH_APT_CONFIG=$(GLOBAL_HSH_APT_CONFIG)"
+	@echo "GLOBAL_HSH_USE_QEMU=$(GLOBAL_HSH_USE_QEMU)"

lib/build.mk

@@ -3,7 +3,7 @@ ANSI_OK   ?= 1;32
 ANSI_FAIL ?= 1;31
 
 MAX_ERRORS = 3
-GOTCHA := ^(((\*\* )?(E:|[Ee]rror|[Ww]arning).*)|(.* (conflicts|Depends:) .*)|(.* (Stop|failed)\.))$$
+GOTCHA := ^(((\*\* )?(E:|[Ee]rror|[Ww]arning).*)|(.* (conflicts|Depends:) .*)|(.* (Stop|failed|not found)\.))$$
 
 ifndef MKIMAGE_PROFILES
 $(error this makefile is designed to be included in toplevel one)
@@ -20,8 +20,13 @@ LOWSPACE = 1024
 # it's also nice to know how long and much it takes
 START += time -f "%E %PCPU %Mk"
 
-ifneq (,$(wildcard $(subst :,/$(ARCH) ,$(PATH):)))
-# /usr/bin/{i586,x86_64} are setarch(8) symlinks but arm is not
+# /usr/bin/{i586,x86_64} are setarch(8) symlinks but arm is not;
+# also check whether non-x86 build is running native
+ifeq (,$(wildcard $(subst :,/$(ARCH) ,$(PATH):)))
+ifeq (,$(findstring $(ARCH),$(shell uname -m)))
+export GLOBAL_HSH_USE_QEMU=$(ARCH)
+endif
+else
 START += $(ARCH)
 endif
 

lib/profile.mk

@@ -52,13 +52,25 @@ profile/init: distclean
 		fi $(LOG); \
 	fi; \
 	{ \
-		eval `apt-config shell $${APTCONF:+-c=$(wildcard $(APTCONF))} \
+		APTCONF="$(wildcard $(APTCONF))"; \
+		echo "** using $${APTCONF:-system apt configuration}:"; \
+		eval `apt-config shell $${APTCONF:+-c=$$APTCONF} \
 			SOURCELIST Dir::Etc::sourcelist/f \
 			SOURCEPARTS Dir::Etc::sourceparts/d`; \
 		find "$$SOURCEPARTS" -name '*.list' \
-		| xargs egrep -Rhv '^#|^[[:blank:]]*$$' "$$SOURCELIST" && \
+		| xargs egrep -Rhv '^#|^[[:blank:]]*$$' "$$SOURCELIST" \
+		| tee $(BUILDDIR)/sources.list; \
 		echo; \
 	} $(LOG); \
+	if ! grep -q "[	 ]$(ARCH)[ 	]" $(BUILDDIR)/sources.list; then \
+		echo -n "requested arch '$$ARCH' unavailable" >&2; \
+		if [ -z "$(APTCONF)" ]; then \
+			echo " (no APTCONF)"; \
+		else \
+			echo; \
+		fi >&2; \
+		exit 1; \
+	fi; \
 	if type -t git >&/dev/null; then \
 		if cd $(BUILDDIR); then \
 			git init -q && \