cbfstool: Add offset field to cbfstool directory's struct buffer

This allows calls to buffer_delete() to work on a buffer that has been
buffer_seek()ed or the buffer created by a buffer_splice(). The same
information could also be useful for other purposes, such as writing
slices back to a file at the offset they originally occupied.

BUG=chromium:470407
TEST=Attempt to perform the following sequence of buffer actions, then run it
through valgrind to check for memory errors:
for (int pos = 0; pos <= 3; ++pos) {
	struct buffer seek_test;
	buffer_create(&seek_test, 3, "seek_test");
	if (pos == 0) {
		buffer_delete(&seek_test);
		continue;
	}
	buffer_seek(&seek_test, 1);
	if (pos == 1) {
		buffer_delete(&seek_test);
		continue;
	}
	buffer_seek(&seek_test, 1);
	if (pos == 2) {
		buffer_delete(&seek_test);
		continue;
	}
	buffer_seek(&seek_test, 1);
	if (pos == 3) {
		buffer_delete(&seek_test);
		continue;
	}
}
for (int pos = 0; pos <= 14; ++pos) {
	struct buffer slice_test;
	buffer_create(&slice_test, 3, "slice_test");
	if (pos == 0) {
		buffer_delete(&slice_test);
		continue;
	}
	struct buffer sliced_once;
	buffer_splice(&sliced_once, &slice_test, 1, 2);
	if (pos == 1) {
		buffer_delete(&slice_test);
		continue;
	}
	if (pos == 2) {
		buffer_delete(&sliced_once);
		continue;
	}
	struct buffer sliced_twice;
	buffer_splice(&sliced_twice, &sliced_once, 2, 1);
	if (pos == 3) {
		buffer_delete(&slice_test);
		continue;
	}
	if (pos == 4) {
		buffer_delete(&sliced_once);
		continue;
	}
	if (pos == 5) {
		buffer_delete(&sliced_twice);
		continue;
	}
	struct buffer sliced_same;
	buffer_splice(&sliced_same, &slice_test, 1, 1);
	if (pos == 6) {
		buffer_delete(&slice_test);
		continue;
	}
	if (pos == 7) {
		buffer_delete(&sliced_once);
		continue;
	}
	if (pos == 8) {
		buffer_delete(&sliced_twice);
		continue;
	}
	if (pos == 9) {
		buffer_delete(&sliced_same);
		continue;
	}
	struct buffer sliced_thrice;
	buffer_splice(&sliced_thrice, &sliced_twice, 1, 0);
	if (pos == 10) {
		buffer_delete(&slice_test);
		continue;
	}
	if (pos == 11) {
		buffer_delete(&sliced_once);
		continue;
	}
	if (pos == 12) {
		buffer_delete(&sliced_twice);
		continue;
	}
	if (pos == 13) {
		buffer_delete(&sliced_same);
		continue;
	}
	if (pos == 14) {
		buffer_delete(&sliced_thrice);
		continue;
	}
}
BRANCH=None

Change-Id: Id67734654a62302c0de37746d8a978d49b240505
Signed-off-by: Sol Boucher <solb@chromium.org>
Original-Commit-Id: 00c40982a21a91a488587dd3cead7109f3a30d98
Original-Change-Id: Ie99839d36500d3270e4924a3477e076a6d27ffc8
Original-Signed-off-by: Sol Boucher <solb@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/267467
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10133
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/cbfstool/common.c

@@ -57,6 +57,7 @@ static off_t get_file_size(FILE *f)
 int buffer_create(struct buffer *buffer, size_t size, const char *name)
 {
 	buffer->name = strdup(name);
+	buffer->offset = 0;
 	buffer->size = size;
 	buffer->data = (char *)malloc(buffer->size);
 	if (!buffer->data) {
@@ -73,6 +74,7 @@ int buffer_from_file(struct buffer *buffer, const char *filename)
 		perror(filename);
 		return -1;
 	}
+	buffer->offset = 0;
 	buffer->size = get_file_size(fp);
 	if (buffer->size == -1u) {
 		fprintf(stderr, "could not determine size of %s\n", filename);
@@ -116,9 +118,10 @@ void buffer_delete(struct buffer *buffer)
 		buffer->name = NULL;
 	}
 	if (buffer->data) {
-		free(buffer->data);
+		free(buffer->data - buffer->offset);
 		buffer->data = NULL;
 	}
+	buffer->offset = 0;
 	buffer->size = 0;
 }