[PATCH] archive-zip: don't use sizeof(struct ...)
- From
René Scharfe <rene.scharfe@lsrfire.ath.cx>
- Date
- Nov 23, 2006, 22:02 UTC
- Message-ID
- <45661A7D.9070207@lsrfire.ath.cx>
- In-Reply-To
- <7vpsbdkhzc.fsf@assigned-by-dhcp.cox.net>
We can't rely on sizeof(struct zip_*) returning the sum of all struct members. At least on ARM padding is added at the end, as Gerrit Pape reported. This fixes the problem but still lets the compiler do the summing by introducing explicit padding at the end of the structs and then taking its offset as the combined size of the preceding members.
As Junio correctly notes, the _end[] marker array's size must be greater than zero for compatibility with compilers other than gcc. The space wasted by the markers can safely be neglected because we only have one instance of each struct, i.e. in sum 3 wasted bytes on i386, and 0 on ARM. :)
We still rely on the compiler to not add padding between the struct members, but that's reasonable given that all of them are unsigned char arrays.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
archive-zip.c | 24 ++++++++++++++++++------ 1 files changed, 18 insertions(+), 6 deletions(-)
diff --git a/archive-zip.c b/archive-zip.c index ae5572a..36e922a 100644 --- a/archive-zip.c +++ b/archive-zip.c @@ -35,6 +35,7 @@ struct zip_local_header { unsigned char size[4]; unsigned char filename_length[2]; unsigned char extra_length[2]; + unsigned char _end[1]; }; struct zip_dir_header { @@ -55,6 +56,7 @@ struct zip_dir_header { unsigned char attr1[2]; unsigned char attr2[4]; unsigned char offset[4]; + unsigned char _end[1]; }; struct zip_dir_trailer { @@ -66,8 +68,18 @@ struct zip_dir_trailer { unsigned char size[4]; unsigned char offset[4]; unsigned char comment_length[2]; + unsigned char _end[1]; }; +/* + * On ARM, padding is added at the end of the struct, so a simple + * sizeof(struct ...) reports two bytes more than the payload size + * we're interested in. + */ +#define ZIP_LOCAL_HEADER_SIZE offsetof(struct zip_local_header, _end) +#define ZIP_DIR_HEADER_SIZE offsetof(struct zip_dir_header, _end) +#define ZIP_DIR_TRAILER_SIZE offsetof(struct zip_dir_trailer, _end) + static void copy_le16(unsigned char *dest, unsigned int n) { dest[0] = 0xff & n; @@ -211,7 +223,7 @@ static int write_zip_entry(const unsigne } /* make sure we have enough free space in the dictionary */ - direntsize = sizeof(struct zip_dir_header) + pathlen; + direntsize = ZIP_DIR_HEADER_SIZE + pathlen; while (zip_dir_size < zip_dir_offset + direntsize) { zip_dir_size += ZIP_DIRECTORY_MIN_SIZE; zip_dir = xrealloc(zip_dir, zip_dir_size); @@ -234,8 +246,8 @@ static int write_zip_entry(const unsigne copy_le16(dirent.attr1, 0); copy_le32(dirent.attr2, attr2); copy_le32(dirent.offset, zip_offset); - memcpy(zip_dir + zip_dir_offset, &dirent, sizeof(struct zip_dir_header)); - zip_dir_offset += sizeof(struct zip_dir_header); + memcpy(zip_dir + zip_dir_offset, &dirent, ZIP_DIR_HEADER_SIZE); + zip_dir_offset += ZIP_DIR_HEADER_SIZE; memcpy(zip_dir + zip_dir_offset, path, pathlen); zip_dir_offset += pathlen; zip_dir_entries++; @@ -251,8 +263,8 @@ static int write_zip_entry(const unsigne copy_le32(header.size, uncompressed_size); copy_le16(header.filename_length, pathlen); copy_le16(header.extra_length, 0); - write_or_die(1, &header, sizeof(struct zip_local_header)); - zip_offset += sizeof(struct zip_local_header); + write_or_die(1, &header, ZIP_LOCAL_HEADER_SIZE); + zip_offset += ZIP_LOCAL_HEADER_SIZE; write_or_die(1, path, pathlen); zip_offset += pathlen; if (compressed_size > 0) { @@ -282,7 +294,7 @@ static void write_zip_trailer(const unsi copy_le16(trailer.comment_length, sha1 ? 40 : 0); write_or_die(1, zip_dir, zip_dir_offset); - write_or_die(1, &trailer, sizeof(struct zip_dir_trailer)); + write_or_die(1, &trailer, ZIP_DIR_TRAILER_SIZE); if (sha1) write_or_die(1, sha1_to_hex(sha1), 40); }