Merge pull request #4076 from kinvolk/rata/smaller-runc-dmz

libct/dmz: Support compiling on all arches

Author: kolyshkin

libcontainer/dmz/Makefile

@@ -1,7 +1,19 @@
-# Get CC values for cross-compilation.
+# Get GO, GOARCH and CC values for cross-compilation.
 include ../../cc_platform.mk
 
-# We use the flags suggested in nolibc/nolibc.h, it makes the binary very small.
+# List of GOARCH that nolibc supports, from:
+# 	https://go.dev/doc/install/source#environment (with GOOS=linux)
+#
+# See nolibc supported arches in ./nolibc/arch-*.h
+NOLIBC_GOARCHES := 386 amd64 arm arm64 loong64 ppc64le riscv64 s390x
+
+ifneq (,$(filter $(GOARCH), $(NOLIBC_GOARCHES)))
+	# We use the flags suggested in nolibc/nolibc.h, it makes the binary very small.
+	CFLAGS += -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib -lgcc
+else
+	CFLAGS += -DRUNC_USE_STDLIB
+endif
+
 runc-dmz: _dmz.c
-	$(CC) $(CFLAGS) -fno-asynchronous-unwind-tables -fno-ident -s -Os -nostdlib -lgcc -static -o $@ $^
+	$(CC) $(CFLAGS) -static -o $@ $^
 	$(STRIP) -gs $@

libcontainer/dmz/README.md

@@ -13,4 +13,6 @@ The current version in that folder is from Linux 6.6-rc3 tag (556fb7131e03b02836
 
 It also support all the architectures we support in runc.
 
+If the GOARCH we use for compiling doesn't support nolibc, it fallbacks to using the C stdlib.
+
 [nolibc-upstream]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/include/nolibc?h=v6.6-rc3

libcontainer/dmz/_dmz.c

@@ -1,5 +1,9 @@
-#include "xstat.h"
-#include "nolibc/nolibc.h"
+#ifdef RUNC_USE_STDLIB
+#  include <unistd.h>
+#else
+#  include "xstat.h"
+#  include "nolibc/nolibc.h"
+#endif
 
 extern char **environ;