usb: gadget: FunctionFS: Remove VLAIS usage from gadget code

The use of variable length arrays in structs (VLAIS) in the Linux Kernel code
precludes the use of compilers which don't implement VLAIS (for instance the
Clang compiler). This alternate patch calculates offsets into the kmalloc-ed
memory buffer using macros. The previous patch required multiple kmalloc and
kfree calls. This version uses "group" vs "struct" since it really is not a
struct and is essentially a group of VLA in a common allocated block. This
version also fixes the issues pointed out by Andrzej Pietrasiewicz and
Michal Nazarewicz.
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
Signed-off-by: Behan Webster <behanw@converseincode.com>

[elimination of miexed declaration and code, checkpatch cleanup]
[fixes after Michal's review]
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/f_fs.c

@@ -30,6 +30,31 @@
 
 #define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest dice roll ;) */
 
+/* Variable Length Array Macros **********************************************/
+#define vla_group(groupname) size_t groupname##__next = 0
+#define vla_group_size(groupname) groupname##__next
+
+#define vla_item(groupname, type, name, n) \
+	size_t groupname##_##name##__offset = ({			       \
+		size_t align_mask = __alignof__(type) - 1;		       \
+		size_t offset = (groupname##__next + align_mask) & ~align_mask;\
+		size_t size = (n) * sizeof(type);			       \
+		groupname##__next = offset + size;			       \
+		offset;							       \
+	})
+
+#define vla_item_with_sz(groupname, type, name, n) \
+	size_t groupname##_##name##__sz = (n) * sizeof(type);		       \
+	size_t groupname##_##name##__offset = ({			       \
+		size_t align_mask = __alignof__(type) - 1;		       \
+		size_t offset = (groupname##__next + align_mask) & ~align_mask;\
+		size_t size = groupname##_##name##__sz;			       \
+		groupname##__next = offset + size;			       \
+		offset;							       \
+	})
+
+#define vla_ptr(ptr, groupname, name) \
+	((void *) ((char *)ptr + groupname##_##name##__offset))
 
 /* Debugging ****************************************************************/
 
@@ -1902,30 +1927,34 @@ static int __ffs_data_got_strings(struct ffs_data *ffs,
 
 	/* Allocate everything in one chunk so there's less maintenance. */
 	{
-		struct {
-			struct usb_gadget_strings *stringtabs[lang_count + 1];
-			struct usb_gadget_strings stringtab[lang_count];
-			struct usb_string strings[lang_count*(needed_count+1)];
-		} *d;
 		unsigned i = 0;
+		vla_group(d);
+		vla_item(d, struct usb_gadget_strings *, stringtabs,
+			lang_count + 1);
+		vla_item(d, struct usb_gadget_strings, stringtab, lang_count);
+		vla_item(d, struct usb_string, strings,
+			lang_count*(needed_count+1));
 
-		d = kmalloc(sizeof *d, GFP_KERNEL);
-		if (unlikely(!d)) {
+		char *vlabuf = kmalloc(vla_group_size(d), GFP_KERNEL);
+
+		if (unlikely(!vlabuf)) {
 			kfree(_data);
 			return -ENOMEM;
 		}
 
-		stringtabs = d->stringtabs;
-		t = d->stringtab;
+		/* Initialize the VLA pointers */
+		stringtabs = vla_ptr(vlabuf, d, stringtabs);
+		t = vla_ptr(vlabuf, d, stringtab);
 		i = lang_count;
 		do {
 			*stringtabs++ = t++;
 		} while (--i);
 		*stringtabs = NULL;
 
-		stringtabs = d->stringtabs;
-		t = d->stringtab;
-		s = d->strings;
+		/* stringtabs = vlabuf = d_stringtabs for later kfree */
+		stringtabs = vla_ptr(vlabuf, d, stringtabs);
+		t = vla_ptr(vlabuf, d, stringtab);
+		s = vla_ptr(vlabuf, d, strings);
 		strings = s;
 	}
 
@@ -2201,16 +2230,16 @@ static int ffs_func_bind(struct usb_configuration *c,
 	int ret;
 
 	/* Make it a single chunk, less management later on */
-	struct {
-		struct ffs_ep eps[ffs->eps_count];
-		struct usb_descriptor_header
-			*fs_descs[full ? ffs->fs_descs_count + 1 : 0];
-		struct usb_descriptor_header
-			*hs_descs[high ? ffs->hs_descs_count + 1 : 0];
-		short inums[ffs->interfaces_count];
-		char raw_descs[high ? ffs->raw_descs_length
-				    : ffs->raw_fs_descs_length];
-	} *data;
+	vla_group(d);
+	vla_item_with_sz(d, struct ffs_ep, eps, ffs->eps_count);
+	vla_item_with_sz(d, struct usb_descriptor_header *, fs_descs,
+		full ? ffs->fs_descs_count + 1 : 0);
+	vla_item_with_sz(d, struct usb_descriptor_header *, hs_descs,
+		high ? ffs->hs_descs_count + 1 : 0);
+	vla_item_with_sz(d, short, inums, ffs->interfaces_count);
+	vla_item_with_sz(d, char, raw_descs,
+		high ? ffs->raw_descs_length : ffs->raw_fs_descs_length);
+	char *vlabuf;
 
 	ENTER();
 
@@ -2218,21 +2247,28 @@ static int ffs_func_bind(struct usb_configuration *c,
 	if (unlikely(!(full | high)))
 		return -ENOTSUPP;
 
-	/* Allocate */
-	data = kmalloc(sizeof *data, GFP_KERNEL);
-	if (unlikely(!data))
+	/* Allocate a single chunk, less management later on */
+	vlabuf = kmalloc(vla_group_size(d), GFP_KERNEL);
+	if (unlikely(!vlabuf))
 		return -ENOMEM;
 
 	/* Zero */
-	memset(data->eps, 0, sizeof data->eps);
-	memcpy(data->raw_descs, ffs->raw_descs + 16, sizeof data->raw_descs);
-	memset(data->inums, 0xff, sizeof data->inums);
-	for (ret = ffs->eps_count; ret; --ret)
-		data->eps[ret].num = -1;
+	memset(vla_ptr(vlabuf, d, eps), 0, d_eps__sz);
+	memcpy(vla_ptr(vlabuf, d, raw_descs), ffs->raw_descs + 16,
+	       d_raw_descs__sz);
+	memset(vla_ptr(vlabuf, d, inums), 0xff, d_inums__sz);
+	for (ret = ffs->eps_count; ret; --ret) {
+		struct ffs_ep *ptr;
+
+		ptr = vla_ptr(vlabuf, d, eps);
+		ptr[ret].num = -1;
+	}
 
-	/* Save pointers */
-	func->eps             = data->eps;
-	func->interfaces_nums = data->inums;
+	/* Save pointers
+	 * d_eps == vlabuf, func->eps used to kfree vlabuf later
+	*/
+	func->eps             = vla_ptr(vlabuf, d, eps);
+	func->interfaces_nums = vla_ptr(vlabuf, d, inums);
 
 	/*
 	 * Go through all the endpoint descriptors and allocate
@@ -2240,10 +2276,10 @@ static int ffs_func_bind(struct usb_configuration *c,
 	 * numbers without worrying that it may be described later on.
 	 */
 	if (likely(full)) {
-		func->function.fs_descriptors = data->fs_descs;
+		func->function.fs_descriptors = vla_ptr(vlabuf, d, fs_descs);
 		ret = ffs_do_descs(ffs->fs_descs_count,
-				   data->raw_descs,
-				   sizeof data->raw_descs,
+				   vla_ptr(vlabuf, d, raw_descs),
+				   d_raw_descs__sz,
 				   __ffs_func_bind_do_descs, func);
 		if (unlikely(ret < 0))
 			goto error;
@@ -2252,10 +2288,10 @@ static int ffs_func_bind(struct usb_configuration *c,
 	}
 
 	if (likely(high)) {
-		func->function.hs_descriptors = data->hs_descs;
+		func->function.hs_descriptors = vla_ptr(vlabuf, d, hs_descs);
 		ret = ffs_do_descs(ffs->hs_descs_count,
-				   data->raw_descs + ret,
-				   (sizeof data->raw_descs) - ret,
+				   vla_ptr(vlabuf, d, raw_descs) + ret,
+				   d_raw_descs__sz - ret,
 				   __ffs_func_bind_do_descs, func);
 		if (unlikely(ret < 0))
 			goto error;
@@ -2268,7 +2304,7 @@ static int ffs_func_bind(struct usb_configuration *c,
 	 */
 	ret = ffs_do_descs(ffs->fs_descs_count +
 			   (high ? ffs->hs_descs_count : 0),
-			   data->raw_descs, sizeof data->raw_descs,
+			   vla_ptr(vlabuf, d, raw_descs), d_raw_descs__sz,
 			   __ffs_func_bind_do_nums, func);
 	if (unlikely(ret < 0))
 		goto error;