Add sanitizer build options for host (#2842)

This PR adds a couple of build variables so host builds can be compiled with the available address sanitisers.

I spent way too much time today trying to track down some odd behaviour with the graphics library virtual screen in MacOS. Since valgrind isn't available, I tried enabling some address sanitisers which I've not used before. Actually seems more effective than valgrind and is supported on both GCC and CLANG (and MacOS). Found the issue immediately.

There are a lot of possible sanitizer options so I've picked some which look most helpful. Also added stack checking. All of this obviously affects build size and runtime speed.

To try this out:

```
export ENABLE_SANITIZERS=1
make clean components-clean
make flash run
```

That's it. `make list-config | grep SANITIZER` will show applicable options.

NB. GCC requires the `libasan` and `libubsan` packages.

**Bug in MacOS getHostAppDir**

Bad len value causes memory corruption, very difficult to track down without valgrind/santizers.

**Fix graphics virtual display handling with 64-bit host**

Small fix found whilst hunting the above bug, affects all 64-bit builds not just MacOS.

Sming/Arch/Host/Components/hostlib/hostlib.c

@@ -44,7 +44,7 @@ size_t getHostAppDir(char* path, size_t bufSize)
 	char sep = '\\';
 #elif defined(__APPLE__)
 	uint32_t size = bufSize;
-	size_t len = _NSGetExecutablePath(path, &size) ? 0 : size;
+	size_t len = _NSGetExecutablePath(path, &size) ? 0 : strlen(path);
 	char sep = '/';
 #else
 	size_t len = readlink("/proc/self/exe", path, bufSize - 1);

Sming/Arch/Host/README.rst

@@ -52,24 +52,26 @@ To find out what options are in force, use ``make list-config``.
 Configuration
 -------------
 
+.. note::
+
+   The following settings are for debugging purposes and are not 'sticky'.
+   Where used, they should generally be defined globally using ``export``.
+
+
 .. envvar:: CLI_TARGET_OPTIONS
 
    Use this to add any custom options to the emulator command line. e.g.:
 
       make run CLI_TARGET_OPTIONS=--help
       make run CLI_TARGET_OPTIONS="--debug=0 --cpulimit=2"
 
-   Note: These settings are not 'sticky'
-
 
 .. envvar:: CLANG_BUILD
 
    0: Use GCC (default)
    1: Use standard ``clang``
    N: Use specific installed version, ``clang-N``
 
-   Note: This setting is not 'sticky'
-
 
 .. envvar:: BUILD64
 
@@ -79,6 +81,33 @@ Configuration
    On MacOS builds are 64-bit only. Default for other systems is 32-bit.
 
 
+.. envvar:: ENABLE_SANITIZERS
+
+   default: 0 (off)
+
+   Enable this option to build with lots of runtime checking.
+
+   This provides some of the capabilities of valgrind but by instrumenting
+   the code when it is compiled, rather than patching at runtime.
+
+   It also links in some additional runtime support libraries.
+
+   Run a full rebuild after changing this setting (or :envvar:`SANITIZERS`)::
+
+       make clean components-clean
+       make
+
+   .. note::
+
+      If using :envvar:`CLANG_BUILD` then all runtime libraries should already be available.
+      For GCC you will also need to install ``libasan`` and ``libubsan``.
+
+
+.. envvar:: SANITIZERS
+
+   Selects which sanitizers are used. See :envvar:`ENABLE_SANITIZERS`.
+
+
 Components
 ----------
 

Sming/Arch/Host/app.mk

@@ -9,6 +9,10 @@ ifneq ($(BUILD64),1)
 LDFLAGS += -m32
 endif
 
+ifeq ($(ENABLE_SANITIZERS),1)
+LDFLAGS += $(foreach s,$(SANITIZERS),-fsanitize=$s)
+endif
+
 # Executable
 TARGET_OUT_0			:= $(FW_BASE)/$(APP_NAME)$(TOOL_EXT)
 

Sming/Arch/Host/build.mk

@@ -54,6 +54,22 @@ CPPFLAGS += \
 	-D_FILE_OFFSET_BITS=64 \
 	-D_TIME_BITS=64
 
+# Sanitizers
+DEBUG_VARS += ENABLE_SANITIZERS SANITIZERS
+ENABLE_SANITIZERS ?= 0
+SANITIZERS ?= \
+	address \
+	pointer-compare \
+	pointer-subtract \
+	leak \
+	undefined
+ifeq ($(ENABLE_SANITIZERS),1)
+CPPFLAGS += \
+	-fstack-protector-all \
+	-fsanitize-address-use-after-scope \
+	$(foreach s,$(SANITIZERS),-fsanitize=$s)
+endif
+
 # => Tools
 MEMANALYZER = size
 

Sming/Wiring/FakePgmSpace.cpp

@@ -19,7 +19,11 @@
 void* memcpy_aligned(void* dst, const void* src, unsigned len)
 {
 	assert(IS_ALIGNED(dst) && IS_ALIGNED(src));
-	memcpy(dst, src, ALIGNUP4(len));
+#ifndef ARCH_HOST
+	// Address sanitisers get tripped if we do this in Host builds
+	len = ALIGNUP4(len);
+#endif
+	memcpy(dst, src, len);
 	return dst;
 }