build: add a sanitizer debug option

Building & running with ASAN is super helpful, so add a dedicated config
knob for it.  This way people don't have to guess at the right compiler
settings in order to get a good build.  We can just tell people to enable
this one option.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Config.in

@@ -688,6 +688,16 @@ config DEBUG_PESSIMIZE
 	  in a much bigger executable that more closely matches the source
 	  code.
 
+config DEBUG_SANITIZE
+	bool "Enable runtime sanitizers (ASAN/LSAN/USAN/etc...)"
+	default n
+	help
+	  Say Y here if you want to enable runtime sanitizers. These help
+	  catch bad memory accesses (e.g. buffer overflows), but will make
+	  the executable larger and slow down runtime a bit.
+
+	  If you aren't developing/testing busybox, say N here.
+
 config UNIT_TEST
 	bool "Build unit tests"
 	default n

Makefile.flags

@@ -75,6 +75,11 @@ else
 CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
 endif
 endif
+ifeq ($(CONFIG_DEBUG_SANITIZE),y)
+CFLAGS += $(call cc-option,-fsanitize=address,)
+CFLAGS += $(call cc-option,-fsanitize=leak,)
+CFLAGS += $(call cc-option,-fsanitize=undefined,)
+endif
 
 # If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
 ARCH_FPIC ?= -fpic