[PATCH 1/2] add MOVE_ARRAY

[PATCH 1/2] add MOVE_ARRAY

[René Scharfe]

Similar to COPY_ARRAY (introduced in 60566cbb58), add a safe and
convenient helper for moving potentially overlapping ranges of array
entries.  It infers the element size, multiplies automatically and
safely to get the size in bytes, does a basic type safety check by
comparing element sizes and unlike memmove(3) it supports NULL
pointers iff 0 elements are to be moved.

Also add a semantic patch to demonstrate the helper's intended usage.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 contrib/coccinelle/array.cocci | 17 +++++++++++++++++
 git-compat-util.h              |  8 ++++++++
 2 files changed, 25 insertions(+)

diff --git a/contrib/coccinelle/array.cocci b/contrib/coccinelle/array.cocci
index 4ba98b7eaf..c61d1ca8dc 100644
--- a/contrib/coccinelle/array.cocci
+++ b/contrib/coccinelle/array.cocci
@@ -27,6 +27,23 @@ expression n;
 
 @@
 type T;
+T *dst;
+T *src;
+expression n;
+@@
+(
+- memmove(dst, src, (n) * sizeof(*dst));
++ MOVE_ARRAY(dst, src, n);
+|
+- memmove(dst, src, (n) * sizeof(*src));
++ MOVE_ARRAY(dst, src, n);
+|
+- memmove(dst, src, (n) * sizeof(T));
++ MOVE_ARRAY(dst, src, n);
+)
+
+@@
+type T;
 T *ptr;
 expression n;
 @@
diff --git a/git-compat-util.h b/git-compat-util.h
index 047172d173..159f82154a 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -825,6 +825,14 @@ static inline void copy_array(void *dst, const void *src, size_t n, size_t size)
 		memcpy(dst, src, st_mult(size, n));
 }
 
+#define MOVE_ARRAY(dst, src, n) move_array((dst), (src), (n), sizeof(*(dst)) + \
+	BUILD_ASSERT_OR_ZERO(sizeof(*(dst)) == sizeof(*(src))))
+static inline void move_array(void *dst, const void *src, size_t n, size_t size)
+{
+	if (n)
+		memmove(dst, src, st_mult(size, n));
+}
+
 /*
  * These functions help you allocate structs with flex arrays, and copy
  * the data directly into the array. For example, if you had:
-- 
2.13.3

[PATCH 2/2] use MOVE_ARRAY

[René Scharfe]

Simplify the code for moving members inside of an array and make it more
robust by using the helper macro MOVE_ARRAY.  It calculates the size
based on the specified number of elements for us and supports NULL
pointers when that number is zero.  Raw memmove(3) calls with NULL can
cause the compiler to (over-eagerly) optimize out later NULL checks.

This patch was generated with contrib/coccinelle/array.cocci and spatch
(Coccinelle).

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
Downside: The one in builtin/ls-files.c papers over a report by UBSan
for the case of istate->cache being NULL.  Technically we still try to
add pos to NULL if pruning an empty index, but we won't see it anymore.
Will send a separate patch.

 builtin/ls-files.c     | 3 +--
 builtin/merge.c        | 2 +-
 builtin/pack-objects.c | 5 ++---
 cache-tree.c           | 5 ++---
 commit.c               | 5 ++---
 notes-merge.c          | 3 +--
 read-cache.c           | 5 ++---
 reflog-walk.c          | 7 +++----
 string-list.c          | 8 +++-----
 9 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index b8514a0029..dc4a6aa3d9 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -378,8 +378,7 @@ static void prune_index(struct index_state *istate,
 		}
 		last = next;
 	}
-	memmove(istate->cache, istate->cache + pos,
-		(last - pos) * sizeof(struct cache_entry *));
+	MOVE_ARRAY(istate->cache, istate->cache + pos, last - pos);
 	istate->cache_nr = last - pos;
 }
 
diff --git a/builtin/merge.c b/builtin/merge.c
index 900bafdb45..d5797b8fe7 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -537,7 +537,7 @@ static void parse_branch_merge_options(char *bmo)
 		die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 		    split_cmdline_strerror(argc));
 	REALLOC_ARRAY(argv, argc + 2);
-	memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
+	MOVE_ARRAY(argv + 1, argv, argc + 1);
 	argc++;
 	argv[0] = "branch.*.mergeoptions";
 	parse_options(argc, argv, NULL, builtin_merge_options,
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index f4a8441fe9..e730b415bf 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1298,9 +1298,8 @@ static int check_pbase_path(unsigned hash)
 		   done_pbase_paths_alloc);
 	done_pbase_paths_num++;
 	if (pos < done_pbase_paths_num)
-		memmove(done_pbase_paths + pos + 1,
-			done_pbase_paths + pos,
-			(done_pbase_paths_num - pos - 1) * sizeof(unsigned));
+		MOVE_ARRAY(done_pbase_paths + pos + 1, done_pbase_paths + pos,
+			   done_pbase_paths_num - pos - 1);
 	done_pbase_paths[pos] = hash;
 	return 0;
 }
diff --git a/cache-tree.c b/cache-tree.c
index ec23d8c03d..2440d1dc89 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -131,9 +131,8 @@ static int do_invalidate_path(struct cache_tree *it, const char *path)
 			 * move 4 and 5 up one place (2 entries)
 			 * 2 = 6 - 3 - 1 = subtree_nr - pos - 1
 			 */
-			memmove(it->down+pos, it->down+pos+1,
-				sizeof(struct cache_tree_sub *) *
-				(it->subtree_nr - pos - 1));
+			MOVE_ARRAY(it->down + pos, it->down + pos + 1,
+				   it->subtree_nr - pos - 1);
 			it->subtree_nr--;
 		}
 		return 1;
diff --git a/commit.c b/commit.c
index cbfd689939..d3150d6270 100644
--- a/commit.c
+++ b/commit.c
@@ -223,9 +223,8 @@ int unregister_shallow(const struct object_id *oid)
 	if (pos < 0)
 		return -1;
 	if (pos + 1 < commit_graft_nr)
-		memmove(commit_graft + pos, commit_graft + pos + 1,
-				sizeof(struct commit_graft *)
-				* (commit_graft_nr - pos - 1));
+		MOVE_ARRAY(commit_graft + pos, commit_graft + pos + 1,
+			   commit_graft_nr - pos - 1);
 	commit_graft_nr--;
 	return 0;
 }
diff --git a/notes-merge.c b/notes-merge.c
index 70e3fbeefb..c12b354f10 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -99,8 +99,7 @@ static struct notes_merge_pair *find_notes_merge_pair_pos(
 	else {
 		*occupied = 0;
 		if (insert_new && i < len) {
-			memmove(list + i + 1, list + i,
-				(len - i) * sizeof(struct notes_merge_pair));
+			MOVE_ARRAY(list + i + 1, list + i, len - i);
 			memset(list + i, 0, sizeof(struct notes_merge_pair));
 		}
 	}
diff --git a/read-cache.c b/read-cache.c
index 2121b6e7bb..acfb028f48 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -515,9 +515,8 @@ int remove_index_entry_at(struct index_state *istate, int pos)
 	istate->cache_nr--;
 	if (pos >= istate->cache_nr)
 		return 0;
-	memmove(istate->cache + pos,
-		istate->cache + pos + 1,
-		(istate->cache_nr - pos) * sizeof(struct cache_entry *));
+	MOVE_ARRAY(istate->cache + pos, istate->cache + pos + 1,
+		   istate->cache_nr - pos);
 	return 1;
 }
 
diff --git a/reflog-walk.c b/reflog-walk.c
index 081f89b70d..81bca2ed23 100644
--- a/reflog-walk.c
+++ b/reflog-walk.c
@@ -111,10 +111,9 @@ static struct commit_info *get_commit_info(struct commit *commit,
 			struct commit_info *result = &lifo->items[i];
 			if (pop) {
 				if (i + 1 < lifo->nr)
-					memmove(lifo->items + i,
-						lifo->items + i + 1,
-						(lifo->nr - i) *
-						sizeof(struct commit_info));
+					MOVE_ARRAY(lifo->items + i,
+						   lifo->items + i + 1,
+						   lifo->nr - i);
 				lifo->nr--;
 			}
 			return result;
diff --git a/string-list.c b/string-list.c
index c650500c6e..806b4c8723 100644
--- a/string-list.c
+++ b/string-list.c
@@ -43,9 +43,8 @@ static int add_entry(int insert_at, struct string_list *list, const char *string
 
 	ALLOC_GROW(list->items, list->nr+1, list->alloc);
 	if (index < list->nr)
-		memmove(list->items + index + 1, list->items + index,
-				(list->nr - index)
-				* sizeof(struct string_list_item));
+		MOVE_ARRAY(list->items + index + 1, list->items + index,
+			   list->nr - index);
 	list->items[index].string = list->strdup_strings ?
 		xstrdup(string) : (char *)string;
 	list->items[index].util = NULL;
@@ -77,8 +76,7 @@ void string_list_remove(struct string_list *list, const char *string,
 			free(list->items[i].util);
 
 		list->nr--;
-		memmove(list->items + i, list->items + i + 1,
-			(list->nr - i) * sizeof(struct string_list_item));
+		MOVE_ARRAY(list->items + i, list->items + i + 1, list->nr - i);
 	}
 }
 
-- 
2.13.3

[PATCH 3/2] apply: use COPY_ARRAY and MOVE_ARRAY in update_image()

[René Scharfe]

Simplify the code by using the helper macros COPY_ARRAY and MOVE_ARRAY,
which also makes them more robust in the case we copy or move no lines,
as they allow using NULL points in that case, while memcpy(3) and
memmove(3) don't.

Found with Clang's UBSan.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
I don't know why the rules in contrib/coccinelle/array.cocci didn't
match. :-?

 apply.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/apply.c b/apply.c
index f2d599141d..40707ca50c 100644
--- a/apply.c
+++ b/apply.c
@@ -2809,13 +2809,10 @@ static void update_image(struct apply_state *state,
 		img->line_allocated = img->line;
 	}
 	if (preimage_limit != postimage->nr)
-		memmove(img->line + applied_pos + postimage->nr,
-			img->line + applied_pos + preimage_limit,
-			(img->nr - (applied_pos + preimage_limit)) *
-			sizeof(*img->line));
-	memcpy(img->line + applied_pos,
-	       postimage->line,
-	       postimage->nr * sizeof(*img->line));
+		MOVE_ARRAY(img->line + applied_pos + postimage->nr,
+			   img->line + applied_pos + preimage_limit,
+			   img->nr - (applied_pos + preimage_limit));
+	COPY_ARRAY(img->line + applied_pos, postimage->line, postimage->nr);
 	if (!state->allow_overlap)
 		for (i = 0; i < postimage->nr; i++)
 			img->line[applied_pos + i].flag |= LINE_PATCHED;
-- 
2.13.3

Re: [PATCH 3/2] apply: use COPY_ARRAY and MOVE_ARRAY in update_image()

[Ramsay Jones]

On 15/07/17 21:20, René Scharfe wrote:
> Simplify the code by using the helper macros COPY_ARRAY and MOVE_ARRAY,
> which also makes them more robust in the case we copy or move no lines,
> as they allow using NULL points in that case, while memcpy(3) and
> memmove(3) don't.
> 
> Found with Clang's UBSan.
> 
> Signed-off-by: Rene Scharfe <l.s.r@web.de>
> ---
> I don't know why the rules in contrib/coccinelle/array.cocci didn't
> match. :-?
> 
>  apply.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/apply.c b/apply.c
> index f2d599141d..40707ca50c 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -2809,13 +2809,10 @@ static void update_image(struct apply_state *state,
>  		img->line_allocated = img->line;
>  	}
>  	if (preimage_limit != postimage->nr)
> -		memmove(img->line + applied_pos + postimage->nr,
> -			img->line + applied_pos + preimage_limit,
> -			(img->nr - (applied_pos + preimage_limit)) *
> -			sizeof(*img->line));
> -	memcpy(img->line + applied_pos,
> -	       postimage->line,
> -	       postimage->nr * sizeof(*img->line));
> +		MOVE_ARRAY(img->line + applied_pos + postimage->nr,
> +			   img->line + applied_pos + preimage_limit,
> +			   img->nr - (applied_pos + preimage_limit));
> +	COPY_ARRAY(img->line + applied_pos, postimage->line, postimage->nr);

My patch looks like:

-       memcpy(img->line + applied_pos,
-              postimage->line,
-              postimage->nr * sizeof(*img->line));
+       if (postimage->line && postimage->nr)
+               memcpy(img->line + applied_pos,
+                      postimage->line,
+                      postimage->nr * sizeof(*img->line));

... which I think I prefer (slightly).


ATB,
Ramsay Jones

>  	if (!state->allow_overlap)
>  		for (i = 0; i < postimage->nr; i++)
>  			img->line[applied_pos + i].flag |= LINE_PATCHED;
> 

Re: [PATCH 3/2] apply: use COPY_ARRAY and MOVE_ARRAY in update_image()

[René Scharfe]

Am 16.07.2017 um 02:31 schrieb Ramsay Jones:
> 
> 
> On 15/07/17 21:20, René Scharfe wrote:
>> Simplify the code by using the helper macros COPY_ARRAY and MOVE_ARRAY,
>> which also makes them more robust in the case we copy or move no lines,
>> as they allow using NULL points in that case, while memcpy(3) and
>> memmove(3) don't.
>>
>> Found with Clang's UBSan.
>>
>> Signed-off-by: Rene Scharfe <l.s.r@web.de>
>> ---
>> I don't know why the rules in contrib/coccinelle/array.cocci didn't
>> match. :-?
>>
>>   apply.c | 11 ++++-------
>>   1 file changed, 4 insertions(+), 7 deletions(-)
>>
>> diff --git a/apply.c b/apply.c
>> index f2d599141d..40707ca50c 100644
>> --- a/apply.c
>> +++ b/apply.c
>> @@ -2809,13 +2809,10 @@ static void update_image(struct apply_state *state,
>>   		img->line_allocated = img->line;
>>   	}
>>   	if (preimage_limit != postimage->nr)
>> -		memmove(img->line + applied_pos + postimage->nr,
>> -			img->line + applied_pos + preimage_limit,
>> -			(img->nr - (applied_pos + preimage_limit)) *
>> -			sizeof(*img->line));
>> -	memcpy(img->line + applied_pos,
>> -	       postimage->line,
>> -	       postimage->nr * sizeof(*img->line));
>> +		MOVE_ARRAY(img->line + applied_pos + postimage->nr,
>> +			   img->line + applied_pos + preimage_limit,
>> +			   img->nr - (applied_pos + preimage_limit));
>> +	COPY_ARRAY(img->line + applied_pos, postimage->line, postimage->nr);
> 
> My patch looks like:
> 
> -       memcpy(img->line + applied_pos,
> -              postimage->line,
> -              postimage->nr * sizeof(*img->line));
> +       if (postimage->line && postimage->nr)
> +               memcpy(img->line + applied_pos,
> +                      postimage->line,
> +                      postimage->nr * sizeof(*img->line));
> 
> ... which I think I prefer (slightly).

Can postimage->line be NULL when postimage->nr is bigger than 0?  What
would that mean?  The only ways to arrive at that point that I an come
up with are bugs (we accidentally set ->line to NULL, or we forgot to
clean ->line).  We'd better notice them early by getting a nice
shrieking segfault.  Adding an assert would work as well.

René

Re: [PATCH 1/2] add MOVE_ARRAY

[Jeff King]

On Sat, Jul 15, 2017 at 09:36:20PM +0200, René Scharfe wrote:

> Similar to COPY_ARRAY (introduced in 60566cbb58), add a safe and
> convenient helper for moving potentially overlapping ranges of array
> entries.  It infers the element size, multiplies automatically and
> safely to get the size in bytes, does a basic type safety check by
> comparing element sizes and unlike memmove(3) it supports NULL
> pointers iff 0 elements are to be moved.
> 
> Also add a semantic patch to demonstrate the helper's intended usage.

If we have COPY_ARRAY(), I think it's foolish not to provide the
matching MOVE_ARRAY().  If it were just the "if (n)", I might say we
could just do this inline in the few calls that care.  But I really like
the size safety.

I agree with your comments elsewhere that we don't need to worry about
the case where one of the arrays is NULL but the size is not zero.
That's a flat-out bug.

-Peff

[PATCH 1/2] add MOVE_ARRAY

[René Scharfe]

Add MOVE_ARRAY to complement COPY_ARRAY, which was added in 60566cbb.
It provides the same convenience, safety and support for NULL pointers
as representations of empty arrays, just as a wrapper for memmove(3)
instead of memcpy(3).

Inspired-by: Martin Liska <mliska@suse.cz>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 git-compat-util.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/git-compat-util.h b/git-compat-util.h
index 8a4a3f85e7..3266a71fb4 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -812,6 +812,14 @@ static inline void copy_array(void *dst, const void *src, size_t n, size_t size)
 		memcpy(dst, src, st_mult(size, n));
 }
 
+#define MOVE_ARRAY(dst, src, n) move_array((dst), (src), (n), sizeof(*(dst)) + \
+	BUILD_ASSERT_OR_ZERO(sizeof(*(dst)) == sizeof(*(src))))
+static inline void move_array(void *dst, const void *src, size_t n, size_t size)
+{
+	if (n)
+		memmove(dst, src, st_mult(size, n));
+}
+
 /*
  * These functions help you allocate structs with flex arrays, and copy
  * the data directly into the array. For example, if you had:
-- 
2.12.2