Merge branch 'jk/clang-sanitizer-fixes' into maint

C pedantry ;-) fix.

* jk/clang-sanitizer-fixes:
  obstack: avoid computing offsets from NULL pointer
  xdiff: avoid computing non-zero offset from NULL pointer
  avoid computing zero offsets from NULL pointer
  merge-recursive: use subtraction to flip stage
  merge-recursive: silence -Wxor-used-as-pow warning

compat/obstack.h

@@ -135,8 +135,10 @@ extern "C" {
    alignment relative to 0.  */
 
 #define __PTR_ALIGN(B, P, A)						    \
-  __BPTR_ALIGN (sizeof (PTR_INT_TYPE) < sizeof (void *) ? (B) : (char *) 0, \
-		P, A)
+  (sizeof (PTR_INT_TYPE) < sizeof(void *) ?                                 \
+   __BPTR_ALIGN((B), (P), (A)) :                                            \
+   (void *)__BPTR_ALIGN((PTR_INT_TYPE)(void *)0, (PTR_INT_TYPE)(P), (A))            \
+  )
 
 #include <string.h>
 

merge-recursive.c

@@ -1712,6 +1712,14 @@ static char *find_path_for_conflict(struct merge_options *opt,
 	return new_path;
 }
 
+/*
+ * Toggle the stage number between "ours" and "theirs" (2 and 3).
+ */
+static inline int flip_stage(int stage)
+{
+	return (2 + 3) - stage;
+}
+
 static int handle_rename_rename_1to2(struct merge_options *opt,
 				     struct rename_conflict_info *ci)
 {
@@ -1756,14 +1764,14 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 		 * such cases, we should keep the added file around,
 		 * resolving the conflict at that path in its favor.
 		 */
-		add = &ci->ren1->dst_entry->stages[2 ^ 1];
+		add = &ci->ren1->dst_entry->stages[flip_stage(2)];
 		if (is_valid(add)) {
 			if (update_file(opt, 0, add, a->path))
 				return -1;
 		}
 		else
 			remove_file_from_index(opt->repo->index, a->path);
-		add = &ci->ren2->dst_entry->stages[3 ^ 1];
+		add = &ci->ren2->dst_entry->stages[flip_stage(3)];
 		if (is_valid(add)) {
 			if (update_file(opt, 0, add, b->path))
 				return -1;
@@ -1776,7 +1784,7 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 		 * rename/add collision.  If not, we can write the file out
 		 * to the specified location.
 		 */
-		add = &ci->ren1->dst_entry->stages[2 ^ 1];
+		add = &ci->ren1->dst_entry->stages[flip_stage(2)];
 		if (is_valid(add)) {
 			add->path = mfi.blob.path = a->path;
 			if (handle_file_collision(opt, a->path,
@@ -1797,7 +1805,7 @@ static int handle_rename_rename_1to2(struct merge_options *opt,
 				return -1;
 		}
 
-		add = &ci->ren2->dst_entry->stages[3 ^ 1];
+		add = &ci->ren2->dst_entry->stages[flip_stage(3)];
 		if (is_valid(add)) {
 			add->path = mfi.blob.path = b->path;
 			if (handle_file_collision(opt, b->path,
@@ -1846,7 +1854,7 @@ static int handle_rename_rename_2to1(struct merge_options *opt,
 	path_side_1_desc = xstrfmt("version of %s from %s", path, a->path);
 	path_side_2_desc = xstrfmt("version of %s from %s", path, b->path);
 	ostage1 = ci->ren1->branch == opt->branch1 ? 3 : 2;
-	ostage2 = ostage1 ^ 1;
+	ostage2 = flip_stage(ostage1);
 	ci->ren1->src_entry->stages[ostage1].path = a->path;
 	ci->ren2->src_entry->stages[ostage2].path = b->path;
 	if (merge_mode_and_contents(opt, a, c1,

sequencer.c

@@ -588,7 +588,7 @@ static int do_recursive_merge(struct repository *r,
 	struct merge_options o;
 	struct tree *next_tree, *base_tree, *head_tree;
 	int clean;
-	char **xopt;
+	int i;
 	struct lock_file index_lock = LOCK_INIT;
 
 	if (repo_hold_locked_index(r, &index_lock, LOCK_REPORT_ON_ERROR) < 0)
@@ -608,8 +608,8 @@ static int do_recursive_merge(struct repository *r,
 	next_tree = next ? get_commit_tree(next) : empty_tree(r);
 	base_tree = base ? get_commit_tree(base) : empty_tree(r);
 
-	for (xopt = opts->xopts; xopt != opts->xopts + opts->xopts_nr; xopt++)
-		parse_merge_opt(&o, *xopt);
+	for (i = 0; i < opts->xopts_nr; i++)
+		parse_merge_opt(&o, opts->xopts[i]);
 
 	clean = merge_trees(&o,
 			    head_tree,

unpack-trees.c

@@ -1350,7 +1350,7 @@ static int clear_ce_flags_1(struct index_state *istate,
 			    enum pattern_match_result default_match,
 			    int progress_nr)
 {
-	struct cache_entry **cache_end = cache + nr;
+	struct cache_entry **cache_end = nr ? cache + nr : cache;
 
 	/*
 	 * Process all entries that have the given prefix and meet

xdiff-interface.c

@@ -84,8 +84,8 @@ static void trim_common_tail(mmfile_t *a, mmfile_t *b)
 {
 	const int blk = 1024;
 	long trimmed = 0, recovered = 0;
-	char *ap = a->ptr + a->size;
-	char *bp = b->ptr + b->size;
+	char *ap = a->size ? a->ptr + a->size : a->ptr;
+	char *bp = b->size ? b->ptr + b->size : b->ptr;
 	long smaller = (a->size < b->size) ? a->size : b->size;
 
 	while (blk + trimmed <= smaller && !memcmp(ap - blk, bp - blk, blk)) {
@@ -250,9 +250,13 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *value, int cflags)
 	ALLOC_ARRAY(regs->array, regs->nr);
 	for (i = 0; i < regs->nr; i++) {
 		struct ff_reg *reg = regs->array + i;
-		const char *ep = strchr(value, '\n'), *expression;
+		const char *ep, *expression;
 		char *buffer = NULL;
 
+		if (!value)
+			BUG("mismatch between line count and parsing");
+		ep = strchr(value, '\n');
+
 		reg->negate = (*value == '!');
 		if (reg->negate && i == regs->nr - 1)
 			die("Last expression must not be negated: %s", value);
@@ -265,7 +269,7 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *value, int cflags)
 		if (regcomp(&reg->re, expression, cflags))
 			die("Invalid regexp to look for hunk header: %s", expression);
 		free(buffer);
-		value = ep + 1;
+		value = ep ? ep + 1 : NULL;
 	}
 }