Timestamps in static libraries

[Erik Cederstrand]

Den 06/10/2010 kl. 08.00 skrev Tim Kientzle:
>> 
>> % diff mod.strings orig.strings
>> 2c2
>> < /               1286312209  0     0     0       958       `
>> ---
>>> /               1269146263  0     0     0       958       `
> 
> That's the timestamp on the pseudo-entry used to store the archive
> symbol table.  (GNU/SysV ar files use a pseudo-entry named "/" to
> store the symbol table.  Since '/' is added to end of names in this
> format, this is essentially an entry with an empty name.)
> 
> The current ar code generates this entry and sets the timestamp
> around line 624 of usr.bin/ar/write.c.
> 
> As far as I can tell, ar itself doesn't care about the timestamp here;
> it's possible that ranlib or ld do care.  If they don't, we could set
> this timestamp to zero always.

Is something like the following acceptable? Without risking changes to buildworld/distribution just now, this would allow me to dump contents of an archive and re-insert them with '0' for mtime, uid and gid before checking checksums, without affecting normal ar behaviour.


erik% svn diff
Index: ar.1
===================================================================
--- ar.1	(revision 213478)
+++ ar.1	(working copy)
@@ -62,6 +62,7 @@
 .Op Fl a Ar position-after
 .Op Fl b Ar position-before
 .Op Fl c
+.Op Fl D
 .Op Fl i Ar position-before
 .Op Fl j
 .Op Fl s
@@ -179,6 +180,14 @@
 .Ar archive .
 The archive's symbol table, if present, is updated to reflect
 the new contents of the archive.
+.It Fl D
+When used in combination with the 
+.Fl r
+option, insterts 0's instead of the real mtime, uid and gid values
+from the members named by arguments
+.Ar files ... .
+This ensures that checksums on the resulting archives are reproducible
+when member contents are identical.
 .It Fl f
 Synonymous with option
 .Fl T .
Index: ar.c
===================================================================
--- ar.c	(revision 213478)
+++ ar.c	(working copy)
@@ -154,7 +154,7 @@
 		}
 	}
 
-	while ((opt = getopt_long(argc, argv, "abCcdfijlMmopqrSsTtuVvxz",
+	while ((opt = getopt_long(argc, argv, "abCcdDfijlMmopqrSsTtuVvxz",
 	    longopts, NULL)) != -1) {
 		switch(opt) {
 		case 'a':
@@ -173,6 +173,9 @@
 		case 'd':
 			set_mode(bsdar, opt);
 			break;
+		case 'D':
+			bsdar->options |= AR_D;
+			break;
 		case 'f':
 		case 'T':
 			bsdar->options |= AR_TR;
@@ -357,8 +360,8 @@
 	(void)fprintf(stderr, "\tar -m [-Tabijsvz] position archive file ...\n");
 	(void)fprintf(stderr, "\tar -p [-Tv] archive [file ...]\n");
 	(void)fprintf(stderr, "\tar -q [-Tcjsvz] archive file ...\n");
-	(void)fprintf(stderr, "\tar -r [-Tcjsuvz] archive file ...\n");
-	(void)fprintf(stderr, "\tar -r [-Tabcijsuvz] position archive file ...\n");
+	(void)fprintf(stderr, "\tar -r [-TcDjsuvz] archive file ...\n");
+	(void)fprintf(stderr, "\tar -r [-TabcDijsuvz] position archive file ...\n");
 	(void)fprintf(stderr, "\tar -s [-jz] archive\n");
 	(void)fprintf(stderr, "\tar -t [-Tv] archive [file ...]\n");
 	(void)fprintf(stderr, "\tar -x [-CTouv] archive [file ...]\n");
Index: ar.h
===================================================================
--- ar.h	(revision 213478)
+++ ar.h	(working copy)
@@ -43,6 +43,7 @@
 #define AR_U	0x0200		/* only extract or update newer members.*/
 #define AR_V	0x0400		/* verbose mode */
 #define AR_Z	0x0800		/* gzip compression */
+#define AR_D	0x1000		/* insert members with dummy mtime, uid and gid */
 
 #define DEF_BLKSZ 10240		/* default block size */
 
Index: write.c
===================================================================
--- write.c	(revision 213478)
+++ write.c	(working copy)
@@ -163,11 +163,22 @@
 	if (mtime != 0 && bsdar->options & AR_U && sb.st_mtime <= mtime)
 		goto giveup;
 
-	obj->uid = sb.st_uid;
-	obj->gid = sb.st_gid;
+	/*
+	 * When modifier -D is specified, mtime and UID / GID from the file
+	 * will be replaced with 0. This ensures that checksums will match 
+	 * for two archives containing the exact same files.
+	*/
+	if (bsdar->options & AR_D) {
+		obj->uid = 0;
+		obj->gid = 0;
+		obj->mtime = 0;
+	} else {
+		obj->uid = sb.st_uid;
+		obj->gid = sb.st_gid;
+		obj->mtime = sb.st_mtime;
+	}
 	obj->md = sb.st_mode;
 	obj->size = sb.st_size;
-	obj->mtime = sb.st_mtime;
 	obj->dev = sb.st_dev;
 	obj->ino = sb.st_ino;
 
@@ -621,7 +632,10 @@
 	    bsdar->options & AR_S) {
 		entry = archive_entry_new();
 		archive_entry_copy_pathname(entry, "/");
-		archive_entry_set_mtime(entry, time(NULL), 0);
+		if (bsdar->options & AR_O)
+			archive_entry_set_mtime(entry, 0, 0);
+		else
+			archive_entry_set_mtime(entry, time(NULL), 0);
 		archive_entry_set_size(entry, (bsdar->s_cnt + 1) *
 		    sizeof(uint32_t) + bsdar->s_sn_sz);
 		AC(archive_write_header(a, entry));


Thanks,
Erik