RFC: Using fixed-length strings for version[] and osrelease[]
From: Colin Percival (cperciva_at_freebsd.org)
Date: 05/20/05
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Date: Thu, 19 May 2005 16:52:33 -0700 To: freebsd-arch@freebsd.org
In vers.c (created by src/sys/conf/newvers.sh), the strings version[] and
osrelease[] are not declared with a fixed length. As a result, as the kernel
moves from x.y-RELEASE to x.y-RELEASE-p1, and later to x.y-RELEASE-p10, the
length of these strings will change; this causes cascading differences in
addresses throughout the kernel binary.
This is not a major problem for most people, but it causes difficulty for
FreeBSD Update. Such cascading differences in addresses cause FreeBSD Update
to recognize the kernel as having changed, at which point it decided that the
new kernel needs to be distributed to everybody -- or rather, it would do this
but for the fact that my FreeBSD Update build code replaces the traditional
"x.y-RELEASE-p15" name with "x.y-SECURITY".
As this is the last remaining place where the files built and distributed by
FreeBSD Update differ from the standard src tree, I'd like to remove the need
for this local patch. At BSDCan last week, Jacques Vidrine pointed out that
this could be done simply by declaring these two strings as having fixed
length -- i.e., by zero-padding them.
Would anyone object to the following patch being applied?
--- newvers.sh 15 Jan 2005 13:25:41 -0000 1.68
+++ newvers.sh 19 May 2005 23:48:21 -0000
@@ -87,9 +87,9 @@ cat << EOF > vers.c
$COPYRIGHT
char sccspad[32 - 4 /* sizeof(sccs) */] = { '\\0' };
char sccs[4] = { '@', '(', '#', ')' };
-char version[] = "${VERSION} #${v}: ${t}\\n ${u}@${h}:${d}\\n";
+char version[512] = "${VERSION} #${v}: ${t}\\n ${u}@${h}:${d}\\n";
char ostype[] = "${TYPE}";
-char osrelease[] = "${RELEASE}";
+char osrelease[64] = "${RELEASE}";
int osreldate = ${RELDATE};
char kern_ident[] = "${i}";
EOF
The lengths 512 and 64 are chosen as being considerably more than double the
likely lengths of these strings; on my system, these two strings are 12 bytes
and 134 bytes long respectively.
Colin Percival
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