factor out kver detection to functions file

This leaves bash completion with a duplication, but this is intentional
to avoid pulling in the entire functions file and worrying about
pollution.

Signed-off-by: Dave Reisner <dreisner@archlinux.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/functions b/functions
index 5a44ac9..8be43ed 100644
--- a/functions
+++ b/functions
@@ -133,6 +133,28 @@ parseopts() {
     return 0
 }
 
+kver() {
+    # this is intentionally very loose. only ensure that we're
+    # dealing with some sort of string that starts with something
+    # resembling dotted decimal notation. remember that there's no
+    # requirement for CONFIG_LOCALVERSION to be set.
+    local kver re='^[[:digit:]]+(\.[[:digit:]]+)+'
+
+    # scrape the version out of the kernel image. locate the offset
+    # to the version string by reading 2 bytes out of image at at
+    # address 0x20E. this leads us to a string of, at most, 128 bytes.
+    # read the first word from this string as the kernel version.
+    local offset=$(hexdump -s 526 -n 2 -e '"%0d"' "$1")
+    [[ $offset = +([0-9]) ]] || return 1
+
+    read kver _ < \
+        <(dd if="$1" bs=1 count=127 skip=$(( offset + 0x200 )) 2>/dev/null)
+
+    [[ $kver =~ $re ]] || return 1
+
+    printf '%s' "$kver"
+}
+
 plain() {
     local mesg=$1; shift
     printf "    $_color_bold$mesg$_color_none\n" "$@" >&1